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Tags
list
5901
2
null
5894
0
null
Edit: I made a presumption before where after 27 tries it would then stop searching thus giving a bias on the results ``` # Number of repeats iters = 10000 results = rep(0,iters) # Ball to search for searchNumber = 27 for(i in 1:iters) { # A random permutation: balls = sample(1:27,iters, replace=T) # Numb...
null
CC BY-SA 2.5
null
2011-01-02T21:55:46.263
2011-01-03T00:10:55.017
2011-01-03T00:10:55.017
null
null
null
5902
2
null
5836
0
null
Try the [directlabels](http://directlabels.r-forge.r-project.org/) package for some more control. As far as the caption goes, if you're automatically generating the graphs, you might simply use it as caption text (in LaTeX or HTML or what have you). Hope this helps.
null
CC BY-SA 2.5
null
2011-01-02T22:56:50.777
2011-01-02T22:56:50.777
null
null
317
null
5903
1
null
null
16
6901
Given two arrays x and y, both of length n, I fit a model y = a + b*x and want to calculate a 95% confidence interval for the slope. This is (b - delta, b + delta) where b is found in the usual way and ``` delta = qt(0.975,df=n-2)*se.slope ``` and se.slope is the standard error in the slope. One way to get the standar...
Confidence intervals for regression parameters: Bayesian vs. classical
CC BY-SA 2.5
null
2011-01-02T23:59:51.453
2012-06-22T14:09:32.070
2011-01-16T14:51:59.780
2116
2617
[ "r", "regression", "bayesian", "confidence-interval", "frequentist" ]
5904
2
null
5903
6
null
If you sample from the posterior of b | y and calculate lims (as you define) it should be same as (b - delta, b + delta). Specifically, if you calculate the posterior distribution of b | y under a flat prior, it is same as the classical sampling distribution of b. For more details refer to: Gelman et al. (2003). Bayesi...
null
CC BY-SA 2.5
null
2011-01-03T01:53:27.830
2011-01-03T13:56:55.263
2011-01-03T13:56:55.263
1307
1307
null
5905
2
null
5899
10
null
To give some context, I don't view this as a "statistical" question as much of a "group preference" question. Economists and policy wonks do a lot of thinking about questions of how to convert individual preferences into a "will of the people." You will find lots of interesting reading if you search the web for "politi...
null
CC BY-SA 2.5
null
2011-01-03T01:59:54.670
2011-02-02T15:44:38.890
2011-02-02T15:44:38.890
660
660
null
5907
2
null
5893
1
null
The amount of information that can be found varies wildly, from just race and gender, to all sorts of personal info. Your best bet at getting the information would be social network sites like facebook, as they generally provide more information than cencus databases.
null
CC BY-SA 2.5
null
2011-01-02T19:30:45.810
2011-01-03T11:13:42.550
null
null
null
null
5908
2
null
5893
1
null
There's quite a wide range of information you can get depending on the sources you use. Census data is an obvious one. You can also get information from Facebook, MySpace and other social networking sites. You could also probably search public news archives for mentions of their name. Maybe even those ubclained propert...
null
CC BY-SA 2.5
null
2011-01-02T19:41:43.203
2011-01-03T11:13:42.550
null
null
null
null
5909
2
null
5893
13
null
This is not a serious answer, but I just remembered something from a book I read a year ago. There is a chapter in [Freakonomics](http://rads.stackoverflow.com/amzn/click/0060731338) devoted to what you can tell about a person from the name. The chapter is based on the author's research paper The causes and consequence...
null
CC BY-SA 2.5
null
2011-01-02T20:43:28.110
2011-01-03T11:13:42.550
null
null
null
null
5910
2
null
5893
2
null
You probably could find out: - Profession and possibly job history, if one participates in any professional discussions (current job usually can be found out from either domain name in email or signature, search would reveal past ones too) - Relatives, if one maintains profile on social networks. - Current location,...
null
CC BY-SA 2.5
null
2011-01-03T01:47:42.210
2011-01-03T11:13:42.550
null
null
null
null
5911
2
null
5893
4
null
Just to add in to other suggestions here, one of the largest sources for family data is the raft of genealogy sites out there. I think most western people are probably listed by some family member, distant or otherwise on a few of them and any such inclusion comes with a usually comprehensive family tree attached, com...
null
CC BY-SA 2.5
null
2011-01-03T03:24:33.477
2011-01-03T11:13:42.550
null
null
null
null
5912
1
5920
null
10
1984
A recent question about [alternatives to logistic regression in R](https://stats.stackexchange.com/questions/2234/alternatives-to-logistic-regression-in-r) yielded a variety of answers including randomForest, gbm, rpart, bayesglm, and generalized additive models. What are the practical and interpretation differences b...
What are the practical & interpretation differences between alternatives and logistic regression?
CC BY-SA 2.5
null
2011-01-03T13:13:27.213
2022-08-15T19:16:51.353
2017-04-13T12:44:48.343
-1
196
[ "r", "hypothesis-testing", "logistic", "random-forest" ]
5913
1
5921
null
7
2985
I’m writing some code (JavaScript) to compare benchmark results. I’m using the [Welch T-test](http://frank.mtsu.edu/~dkfuller/notes302/welcht.pdf) because the variance and/or sample size between benchmarks is most likely different. The critical value is pulled from a T-distribution table at 95% confidence (two-sided). ...
Interpreting two-sided, two-sample, Welch T-Test
CC BY-SA 2.5
null
2011-01-03T13:17:49.960
2011-01-04T18:48:40.033
2017-04-13T12:44:52.277
-1
2616
[ "distributions", "t-test", "javascript" ]
5915
2
null
5913
6
null
Dividing by 2 is for p-values. If you compare critical values the division by 2 is not necessary. The function `getCriticalValue` should be the [quantile function](http://en.wikipedia.org/wiki/Quantile_function) of Student's t distribution. Thus it should take 2 values, the probability and the degrees of freedom. If yo...
null
CC BY-SA 2.5
null
2011-01-03T13:56:58.953
2011-01-03T13:56:58.953
null
null
2116
null
5916
2
null
5913
6
null
It's not absolutely necessary to round the degrees of freedom to an integer. [Student's t-distribution](http://en.wikipedia.org/wiki/Student%27s_t-distribution) can be defined for all positive real values of this parameter. Restricting it to a positive integer may make the critical value easier to calculate though, dep...
null
CC BY-SA 2.5
null
2011-01-03T14:16:02.377
2011-01-03T14:16:02.377
null
null
449
null
5917
2
null
5899
2
null
You're asking an intriguing question. I agree with the comments that are showing some apprehension at the "one-man-one-vote" system. I also agree that knowing the basic statistics (like standard deviation and mean) will not give you an insight into the will of the voters. I would like to play off of David James's answe...
null
CC BY-SA 2.5
null
2011-01-03T15:06:52.347
2011-01-03T15:06:52.347
null
null
2591
null
5918
1
5988
null
24
8646
Note: Case is n>>p I am reading Elements of Statistical Learning and there are various mentions about the "right" way to do cross validation( e.g. page 60, page 245). Specifically, my question is how to evaluate the final model (without a separate test set) using k-fold CV or bootstrapping when there has been a model s...
Cross Validation (error generalization) after model selection
CC BY-SA 4.0
null
2011-01-03T15:08:29.897
2018-10-25T09:30:53.700
2018-10-25T09:30:53.700
128677
2040
[ "machine-learning", "model-selection", "data-mining", "cross-validation" ]
5920
2
null
5912
9
null
Disclaimer: It is certainly far from being a full answer to the question! I think there are at least two levels to consider before establishing a distinction between all such methods: - whether a single model is fitted or not: This helps opposing methods like logistic regression vs. RF or Gradient Boosting (or more ge...
null
CC BY-SA 4.0
null
2011-01-03T15:39:49.363
2022-08-15T19:16:51.353
2022-08-15T19:16:51.353
79696
930
null
5921
2
null
5913
9
null
(1a) You don't need the Welch test to cope with different sample sizes. That's automatically handled by the Student t-test. (1b) If you think there's a real chance the variances in the two populations are strongly different, then you are assuming a priori that the two populations differ. It might not be a difference ...
null
CC BY-SA 2.5
null
2011-01-03T15:45:13.360
2011-01-03T17:38:42.127
2011-01-03T17:38:42.127
919
919
null
5922
1
6045
null
11
891
A colleague in applied statistics sent me this: > "I was wondering if you know any way to find out the true dimension of the domain of a function. For example, a circle is a one dimensional function in a two dimensional space. If I do not know how to draw, is there a statistic that I can compute that ...
Estimating the dimension of a data set
CC BY-SA 2.5
null
2011-01-03T15:47:12.577
2021-08-21T19:40:50.943
2021-08-21T19:40:50.943
11887
null
[ "large-data", "high-dimensional", "dimensions" ]
5923
2
null
5903
10
null
The 'problem' is in the prior on sigma. Try a less informative setting ``` tau ~ dgamma(1.0E-3,1.0E-3) sigma <- pow(tau, -1/2) ``` in your jags file. Then update a bunch ``` update(10000) ``` grab the parameters, and summarise your quantity of interest. It should line up reasonably well with the classic version. ...
null
CC BY-SA 3.0
null
2011-01-03T15:54:07.543
2012-06-22T14:09:32.070
2012-06-22T14:09:32.070
1739
1739
null
5924
2
null
5922
7
null
[Principal Components Analysis](http://en.wikipedia.org/wiki/Principal_component_analysis) of local data is a good point of departure. We have to take some care, though, to distinguish local (intrinsic) from global (extrinsic) dimension. In the example of points on a circle, the local dimension is 1, but overall the ...
null
CC BY-SA 2.5
null
2011-01-03T16:03:25.970
2011-01-03T16:03:25.970
null
null
919
null
5925
2
null
5859
10
null
The choice of the survival model should be guided by the underlying phenomenon. In this case it appears to be continuous, even if the data is collected in a somewhat discrete manner. A resolution of one month would be just fine over a 5-year period. However, the large number of ties at 6 and 12 months makes one wonder ...
null
CC BY-SA 2.5
null
2011-01-03T16:07:14.337
2011-01-03T16:07:14.337
null
null
279
null
5926
1
null
null
11
24195
The dependent variables in a MANOVA should not be "too strongly correlated". But how strong a correlation is too strong? It would be interesting to get people's opinions on this issue. For instance, would you proceed with MANOVA in the following situations? - Y1 and Y2 are correlated with $r=0.3$ and $p<0.005$ - Y1 ...
MANOVA and correlations between dependent variables: how strong is too strong?
CC BY-SA 3.0
null
2011-01-03T17:12:09.590
2019-10-15T17:51:53.403
2014-10-27T11:57:01.623
28666
266
[ "correlation", "anova", "multivariate-analysis", "rule-of-thumb", "manova" ]
5927
1
null
null
2
555
Are there meaningful ways to quantify how "flat" the log likelihood function is around the MLE when the parameter has more than one dimension? In particular is the determinant of the Hessian a reasonable measure?
A measure of the "flatness" of log likelihood at the MLE
CC BY-SA 2.5
null
2011-01-03T18:01:37.370
2011-01-03T18:34:48.363
null
null
1004
[ "maximum-likelihood" ]
5929
2
null
5927
4
null
You might find that the [Fisher Information](http://en.wikipedia.org/wiki/Fisher_information) has some properties you like. Its the expectation that gives Fisher Information its interpretation as the 'informativeness' of a measurement. But if you're just looking for something geometrically descriptive then your sugges...
null
CC BY-SA 2.5
null
2011-01-03T18:25:09.920
2011-01-03T18:34:48.363
2011-01-03T18:34:48.363
1739
1739
null
5931
2
null
4519
4
null
I may, after all this time, finally have understood the question. The data, if I'm correct, are a set of tuples $(i, j, y(i,j))$ where $i$ is one player, $j \ne i$ is another player, and $y(i,j)$ is the number of attacks of $i$ on $j$. In this notation the objective is to relate $y(i,j)$ to $y(j,i)$. There are some ...
null
CC BY-SA 2.5
null
2011-01-03T19:53:37.627
2011-01-03T19:53:37.627
2020-06-11T14:32:37.003
-1
919
null
5932
2
null
4844
6
null
First, it's almost impossible to drive a car "randomly." Did you periodically consult a random number generator to determine what direction to head in next? I don't think so. This calls into question the use of any statistical procedure that assumes randomness (even if it isn't simple and could lead to dependence). ...
null
CC BY-SA 4.0
null
2011-01-03T20:11:46.050
2022-08-18T20:59:10.793
2022-08-18T20:59:10.793
79696
919
null
5933
2
null
5893
4
null
The last chapter of Freakonomics (2005, Steven D. Levitt and Stephen J. Dubner) has a fascinating discussion about names, particularly as they relate to socio-economic status and race. They have a list of first names that might or might not correlate well with FB's analysis of last names. They also describe how name ch...
null
CC BY-SA 2.5
null
2011-01-03T20:34:28.793
2011-01-03T20:34:28.793
null
null
2591
null
5934
1
5942
null
4
25090
Over the holidays I played a dice game where each player had 3 to 7 d6 to roll each turn. The game gave certain advantages to doubles and triples. I wanted to know the odds of rolling doubles or triples given N dice to understand the importance of "upgrading" to more dice. My question is really about how to reason ab...
Odds of rolling doubles or triples given N 6-sided dice
CC BY-SA 2.5
null
2011-01-03T21:54:58.037
2011-01-04T01:04:18.533
null
null
2622
[ "probability", "games", "dice" ]
5935
1
5936
null
41
44088
I am analyzing an experimental data set. The data consists of a paired vector of treatment type and a binomial outcome: ``` Treatment Outcome A 1 B 0 C 0 D 1 A 0 ... ``` In the outcome column, 1 denotes a success and 0 denotes a failure. I'd like to figure out ...
ANOVA on binomial data
CC BY-SA 2.5
null
2011-01-03T22:04:01.343
2020-02-09T15:23:30.847
2020-02-09T15:23:30.847
11887
2624
[ "logistic", "anova", "data-transformation", "binomial-distribution", "experiment-design" ]
5936
2
null
5935
22
null
No to ANOVA, which assumes a normally distributed outcome variable (among other things). There are "old school" transformations to consider, but I would prefer logistic regression (equivalent to a chi square when there is only one independent variable, as in your case). The advantage of using logistic regression over a...
null
CC BY-SA 3.0
null
2011-01-03T22:21:28.357
2012-06-26T17:23:42.433
2012-06-26T17:23:42.433
7290
2040
null
5937
1
5940
null
44
38113
When teaching an introductory level class, the teachers I know tend to invent some numbers and a story in order to exemplify the method they are teaching. What I would prefer is to tell a real story with real numbers. However, these stories needs to relate to a very tiny dataset, which enables manual calculations. An...
Tiny (real) datasets for giving examples in class?
CC BY-SA 3.0
null
2011-01-03T22:23:41.990
2015-11-17T21:10:43.313
2015-11-17T21:10:43.313
22468
253
[ "dataset", "references", "teaching" ]
5938
2
null
5937
13
null
For two-way tables, I like the data on gender and survival of the titanic passengers: ``` | Alive Dead | Total -------+-------------+------ Female | 308 154 | 462 Male | 142 709 | 851 -------+-------------+------ Total | 450 863 | 1313 ``` With this data, one can discuss things like the chi-sq...
null
CC BY-SA 2.5
null
2011-01-03T22:58:26.610
2011-01-03T22:58:26.610
null
null
1934
null
5939
2
null
1164
9
null
Wooldridge "Introductory Econometrics - A Modern Approach" 2E p.261. If Heteroskedasticity-robust standard errors are valid more often than the usual OLS standard errors, why do we bother we the usual standard errors at all?...One reason they are still used in cross sectional work is that, if the homoskedasticity assum...
null
CC BY-SA 2.5
null
2011-01-03T23:00:01.527
2011-01-03T23:00:01.527
null
null
null
null
5940
2
null
5937
27
null
The [data and story library](http://lib.stat.cmu.edu/DASL/) is an " online library of datafiles and stories that illustrate the use of basic statistics methods". This site seems to have what you need, and you can search it for particular data sets.
null
CC BY-SA 3.0
null
2011-01-03T23:03:39.257
2011-10-28T19:49:33.923
2011-10-28T19:49:33.923
1381
1381
null
5941
2
null
5937
9
null
The [Journal of Statistical Education](http://www.amstat.org/publications/jse/jse_data_archive.htm) has an archive of educational data sets.
null
CC BY-SA 2.5
null
2011-01-03T23:07:43.137
2011-01-03T23:07:43.137
null
null
1381
null
5942
2
null
5934
6
null
You are looking at a much more manageable version of the famous [birthday problem](http://en.wikipedia.org/wiki/Birthday_problem), which has 365 choices for each "die". The link describes the solution as well. In short, the trick for counting duplicates is to rather counting the cases without a duplicate - that is much...
null
CC BY-SA 2.5
null
2011-01-03T23:12:30.220
2011-01-03T23:12:30.220
null
null
279
null
5943
2
null
5937
23
null
There's a book called "A Handbook of Small Datasets" by D.J. Hand, F. Daly, A.D. Lunn, K.J. McConway and E. Ostrowski. The Statistics department at NCSU have electronically posted the datasets from this book [here](http://www.stat.ncsu.edu/sas/sicl/data/). The website above gives only the data; you would need to read...
null
CC BY-SA 2.5
null
2011-01-03T23:15:30.717
2011-01-03T23:15:30.717
null
null
null
null
5944
2
null
5935
3
null
I would like to differ from what you think about Chi-Sq test. It is applicable even if the data is not binomial. It's based on the asymptotic normality of mle (in most of the cases). I would do a logistic regression like this: $$\log \frac {\hat{\pi}} {1-\hat{\pi}} = \beta_0 + \beta_1 \times D_1 + \beta_2 \times D_2$$...
null
CC BY-SA 2.5
null
2011-01-03T23:27:03.747
2011-01-03T23:40:57.383
2011-01-03T23:40:57.383
1307
1307
null
5945
1
5950
null
13
6363
SVMs for classification make intuitive sense to me: I understand how minimizing $||\theta||^2$ yields the maximum margin. However, I don't understand that objective in the context of regression. Various texts ([here](http://kernelsvm.tripod.com/) and [here](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.99.20...
Understanding SVM regression: objective function and "flatness"
CC BY-SA 2.5
null
2011-01-03T23:31:11.083
2019-08-09T08:52:20.067
null
null
1720
[ "regression", "svm" ]
5946
2
null
5680
34
null
Like other parametric tests, the analysis of variance assumes that the data fit the normal distribution. If your measurement variable is not normally distributed, you may be increasing your chance of a false positive result if you analyze the data with an anova or other test that assumes normality. Fortunately, an anov...
null
CC BY-SA 3.0
null
2011-01-04T00:00:42.387
2013-02-26T10:54:57.397
2013-02-26T10:54:57.397
2669
null
null
5947
2
null
5934
5
null
You're really asking for instruction in [combinatorics](http://en.wikipedia.org/wiki/Combinatorics), which is a vast field. For this particular problem, a good method, if somewhat abstract, is to use [generating functions](http://en.wikipedia.org/wiki/Probability-generating_function). The probability generating funct...
null
CC BY-SA 2.5
null
2011-01-04T00:35:45.310
2011-01-04T00:35:45.310
2017-04-13T12:19:38.800
-1
919
null
5948
2
null
5934
6
null
You have posed the kind of combinatorics question that profs will ask you as an undergrad. Let's reduce the problem to doubles of two dice. Instead of asking about doubles, let's ask how not to roll doubles. There are 6 ways to roll the first die and 5 ways (excluding the first die's roll) to roll the second die. Becau...
null
CC BY-SA 2.5
null
2011-01-04T01:04:18.533
2011-01-04T01:04:18.533
null
null
2591
null
5949
2
null
5937
4
null
Probably such an obvious answer that it does not really need to be mentioned, but for correlation or linear regression [Anscombe's quartet](http://en.wikipedia.org/wiki/Anscombe%27s_quartet) is a logical choice. Although it is not a real story with real data I think it is such a simple example it would reasonably fit i...
null
CC BY-SA 2.5
null
2011-01-04T04:04:56.267
2011-01-04T04:04:56.267
null
null
1036
null
5950
2
null
5945
11
null
One way that I think about the flatness is that it makes my predictions less sensitive to perturbations in the features. That is, if I am constructing a model of the form $$y = x^\top \theta + \epsilon,$$ where my feature vector $x$ has already been normalized, then smaller values in $\theta$ mean my model is less sens...
null
CC BY-SA 2.5
null
2011-01-04T05:22:41.427
2011-01-14T17:48:48.753
2011-01-14T17:48:48.753
795
795
null
5951
2
null
5922
3
null
I'm not sure about the 'domain of a function' part, but [Hausdorff Dimension](http://en.wikipedia.org/wiki/Hausdorff_dimension) seems to answer this question. It has the odd property of agreeing with simple examples (e.g. the circle has Hausdorff Dimension 1), but of giving non-integral results for some sets ('fractals...
null
CC BY-SA 2.5
null
2011-01-04T05:28:07.677
2011-01-04T05:28:07.677
null
null
795
null
5952
1
5956
null
10
6213
Is there a way of plotting the regression line of a piecewise model like this, other than using `lines` to plot each segment separately, or using `geom_smooth(aes(group=Ind), method="lm", fill=FALSE)` ? ``` m.sqft <- mean(sqft) model <- lm(price~sqft+I((sqft-m.sqft)*Ind)) # sqft, price: continuous variables, Ind: if sq...
Plotting a piecewise regression line
CC BY-SA 2.5
null
2011-01-04T08:14:55.153
2011-01-05T10:31:19.180
2011-01-05T10:31:19.180
339
339
[ "r", "data-visualization", "regression" ]
5954
1
null
null
47
1507
How can a regression model be any use if you don't know the function you are trying to get the parameters for? I saw a piece of research that said that mothers who breast fed their children were less likely to suffer diabetes in later life. The research was from a survey of some 1000 mothers and controlled for miscella...
Understanding regressions - the role of the model
CC BY-SA 4.0
null
2011-01-04T09:29:01.153
2019-08-08T14:41:28.020
2019-08-08T14:41:28.020
11887
2629
[ "regression", "modeling", "epidemiology", "log-linear" ]
5955
2
null
5954
44
null
It helps to view regression as a linear approximation of the true form. Suppose the true relationship is $$y=f(x_1,...,x_k)$$ with $x_1,...,x_k$ factors explaining the $y$. Then first order Taylor approximation of $f$ around zero is: $$f(x_1,...,x_k)=f(0,...,0)+\sum_{i=1}^{k}\frac{\partial f(0)}{\partial x_k}x_k+\vare...
null
CC BY-SA 2.5
null
2011-01-04T09:45:18.260
2011-01-04T09:45:18.260
null
null
2116
null
5956
2
null
5952
6
null
The only way I know how to do this easily is to predict from the model across the range of `sqft` and plot the predictions. There isn't a general way with `abline` or similar. You might also take a look at the [segmented](http://cran.r-project.org/web/packages/segmented/index.html) package which will fit these models a...
null
CC BY-SA 2.5
null
2011-01-04T09:58:53.000
2011-01-04T12:26:42.980
2011-01-04T12:26:42.980
1390
1390
null
5957
2
null
5954
15
null
An excellent first question! I agree with mpiktas's answer, i.e. the short answer is "they don't, but they hope to have an approximation to the right model that gives approximately the right answer". In the jargon of epidemiology, this model uncertainty is one source of what's known as 'residual confounding'. See [Ste...
null
CC BY-SA 3.0
null
2011-01-04T10:38:37.040
2012-07-01T11:44:17.527
2012-07-01T11:44:17.527
449
449
null
5958
2
null
5954
18
null
The other side of the answer, complementary to mpiktas's answer but not mentioned so far, is: "They don't, but as soon as they assume some model structure, they can check it against the data". The two basic things that could go wrong are: The form of the function, e.g. it's not even linear in logs. So you'd start b...
null
CC BY-SA 2.5
null
2011-01-04T12:06:35.013
2011-01-04T12:06:35.013
null
null
1739
null
5959
2
null
5854
12
null
You might also want to have a look at [beanplots](http://www.jstatsoft.org/v28/c01/paper). ![alt text](https://i.stack.imgur.com/W4Bf8.jpg) [[Source](http://jnlnet.wordpress.com/2008/11/30/beanplots/)] Implemented in [R package](http://cran.r-project.org/web/packages/beanplot/index.html) by Peter Kampstra.
null
CC BY-SA 2.5
null
2011-01-04T12:37:08.117
2011-01-04T12:37:08.117
null
null
22
null
5960
1
5966
null
58
46833
I understand that once we plot the values as a chart, we can identify a bimodal distribution by observing the twin-peaks, but how does one find it programmatically? (I am looking for an algorithm.)
How to identify a bimodal distribution?
CC BY-SA 3.0
null
2011-01-04T13:03:59.157
2022-08-03T13:26:32.640
2011-12-21T17:31:11.937
930
2535
[ "distributions" ]
5961
2
null
5913
2
null
I'm working with the OP on the benchmarking project and wanted to thank you all for clearing some things up. Also I wanted to provide a bit more information in case that affects the advice. The sample size ranges from 5 - 700+ (as many as can be completed in 8 seconds or until the margin of error is at or below 1%. The...
null
CC BY-SA 2.5
null
2011-01-04T13:04:57.233
2011-01-04T18:48:40.033
2020-06-11T14:32:37.003
-1
2634
null
5962
1
5992
null
12
1696
I have 12 positive training sets (cancer cells treated with drugs with each of 12 different mechanisms of action). For each of these positive training sets, I would like to train a support-vector machine to distinguish it from a negative set of equal size sampled from the experiment. Each set has between 1000 and 600...
Should an SVM grid search show a high-accuracy region with low accuracies around?
CC BY-SA 2.5
null
2011-01-04T14:06:34.460
2011-01-05T00:57:32.817
null
null
220
[ "svm" ]
5963
2
null
5960
0
null
The definition in wiki is slightly confusing to me. The probability of a continous data set having just one mode is zero. A simple way to program a bimodal distrubiton is with two seperate normal distributions centered differently. This creates two peaks or what wiki calls modes. You can actually use almost any two...
null
CC BY-SA 2.5
null
2011-01-04T14:58:43.317
2011-01-04T14:58:43.317
null
null
2539
null
5964
2
null
5954
13
null
There is the famous quote "Essentially, all models are wrong, but some are useful" of [George Box](http://en.wikiquote.org/wiki/George_Box). When fitting models like this, we try to (or should) think about the data generation process and the physical, real world, relationships between the response and covariates. We tr...
null
CC BY-SA 2.5
null
2011-01-04T15:34:50.540
2011-01-04T15:34:50.540
null
null
1390
null
5966
2
null
5960
34
null
Identifying a mode for a continuous distribution requires smoothing or binning the data. Binning is typically too procrustean: the results often depend on where you place the bin cutpoints. [Kernel smoothing](http://en.wikipedia.org/wiki/Kernel_smoother) (specifically, in the form of [kernel density estimation](http://...
null
CC BY-SA 4.0
null
2011-01-04T16:44:31.697
2022-08-03T13:26:32.640
2022-08-03T13:26:32.640
919
919
null
5967
1
6002
null
5
2341
We are working on a multivariate linear regression model. Our objective is to forecast the quarterly % growth in mortgage loans outstanding. The independent variables are: 1) Dow Jones level. 2) % change in Dow Jones over past quarter. 3) Case Shiller housing price index. 4) % change in Case Shiller housing price in...
Can you use heteroskedastic time series variables within a regression model?
CC BY-SA 2.5
null
2011-01-04T16:55:36.283
2011-01-05T12:06:14.560
null
null
1329
[ "regression", "multicollinearity", "stepwise-regression", "heteroscedasticity" ]
5968
2
null
3140
2
null
``` load fisheriris indices = crossvalind('Kfold',species,10); cp = classperf(species); % initializes the CP object for i = 1:10 test = (indices == i); train = ~test; class = knnclassify(meas(test,:),meas(train,:),species(train)); % updates the CP object with the current classification results classperf...
null
CC BY-SA 2.5
null
2011-01-04T17:01:30.713
2011-01-04T19:11:00.380
2011-01-04T19:11:00.380
930
null
null
5969
1
6001
null
10
2360
I do quasi-experimental individual differences psychology research. I examine how people who differ in a cognitive ability (that I measure) perform on another task that always at least involves within-subject manipulations (and sometimes between-subject)–DVs are usually response time and/or accuracy. For this question ...
How should I analyze repeated-measures individual differences experiments?
CC BY-SA 2.5
null
2011-01-04T17:37:50.460
2011-01-06T22:33:36.143
2011-01-05T15:21:18.433
2322
2322
[ "repeated-measures" ]
5970
2
null
5680
2
null
Juan has offered a lot, although I'll echo others and repeat that for best accuracy the variables themselves can be nonnormal as long as their residuals aren't. Also, a simplified and slightly more structured answer (via an annotated flow chart) is available at [yellowbrickstats.com](http://yellowbrickstats.com).
null
CC BY-SA 3.0
null
2011-01-04T17:44:03.453
2012-03-29T23:13:14.170
2012-03-29T23:13:14.170
2669
2669
null
5971
1
null
null
1
353
I'm doing some software testing where we are measuring specific latencies. Generally we run the same test several times to just eyeball the results and make sure that they are consistent across runs. I usually do this by plotting the cumulative distributions for each run together on a graph, and look for an anomalies...
What is a good measure (or set of measures) for the difference between two sample sets?
CC BY-SA 2.5
null
2011-01-04T17:45:49.020
2011-01-04T20:03:10.713
null
null
2638
[ "statistical-significance" ]
5972
1
5986
null
7
2330
Let's say we have two biased coins. The probability of tossing a head on the first coin is $\alpha$ and the probability of tossing a head on the second coin is $1-\alpha$. We toss both coins $n$ times and we say that there is a success when there is a head on both coins. If we denote this random variable by $X$ then $$...
Estimation of probability of a success in binomial distribution
CC BY-SA 2.5
null
2011-01-04T17:50:44.507
2011-01-13T23:11:34.813
2011-01-13T23:11:34.813
919
1643
[ "estimation", "binomial-distribution", "unbiased-estimator" ]
5973
2
null
5918
5
null
I have been doing an extensive cross-validation analysis on a data set that cost millions to acquire, and there is no external validation set available. In this case, I performed extensive nested cross validation to ensure validity. I selected features and optimized parameters only from the respective training sets. Th...
null
CC BY-SA 2.5
null
2011-01-04T18:25:18.910
2011-01-04T18:25:18.910
null
null
2643
null
5974
2
null
5971
1
null
what kind of output are you getting? are you using regression? if you're trying to measure which set is best to use, you can use an F test using the sample errors, but I'm not sure what exactly you're taking about.
null
CC BY-SA 2.5
null
2011-01-04T18:26:12.340
2011-01-04T18:26:12.340
null
null
2644
null
5975
1
null
null
3
1760
This probably seems like a really strange question, but let me try to explain what I want to do; hopefully it will make sense. I have a data set with a couple dozen variables, such as age, level of education, self-assessed (via a Likert scale) measures of technical ability, experience, willingness to share personal inf...
Regression with an unknown dependent variable - estimating "likelihood" to do something
CC BY-SA 4.0
null
2011-01-04T18:26:50.577
2019-07-25T10:13:07.933
2019-07-25T10:13:07.933
11887
2641
[ "regression", "multivariate-analysis", "correspondence-analysis" ]
5976
2
null
5975
2
null
The simplest approach would be to do a literature search and see if someone else developed a model with your variables, and then generate predictions based on those prior models. Another possibility would be to make your own model from another data source that does have the required information, and then use that to ge...
null
CC BY-SA 2.5
null
2011-01-04T18:35:41.397
2011-01-04T18:35:41.397
null
null
1036
null
5977
2
null
5967
0
null
well, to try and help, with heteroskedasticity present, the least squares estimators are still unbiased but no longer most efficient, they no longer have smallest variance violating part of the Gauss Markov theorum. I could be wrong, but I believe you're standard errors are more effected by multicollinearity than heter...
null
CC BY-SA 2.5
null
2011-01-04T18:43:15.373
2011-01-04T18:43:15.373
null
null
2644
null
5979
2
null
5680
8
null
Specifically regarding error rates as a DV, [Dixon (2008)](http://linkinghub.elsevier.com/retrieve/pii/S0749596X07001283) very cogently demonstrates that null hypothesis testing via ANOVA can cause both increased false alarm rates (calling effects "significant" when they're not) and increased miss rates (missing real e...
null
CC BY-SA 2.5
null
2011-01-04T19:01:59.580
2011-01-04T19:01:59.580
null
null
364
null
5980
2
null
5967
1
null
You are trying to mix level and flow data in one regression. Just notice, that the percent change could be considered as a certain transformation of the level variable (like returns and log-returns in financial econometrics). So since your dependent variable is % change, when you include levels, they try to "mimic" sta...
null
CC BY-SA 2.5
null
2011-01-04T19:07:38.950
2011-01-04T20:24:38.007
2011-01-04T20:24:38.007
2645
2645
null
5982
1
5996
null
2
1103
We are trying to make simulation experiment involving a common stochastic trend, that is described by the random walk (or $I(1)$ process) $Y_t = Y_{t-1} + \varepsilon_t$, where innovations $\varepsilon_t$ ~ $N(0,1)$. However when could we be sure that the past innovations are more or less reasonably included into the s...
Burn-in period for random walk
CC BY-SA 2.5
null
2011-01-04T19:21:07.543
2011-01-21T08:46:29.903
2011-01-21T08:46:29.903
2645
2645
[ "time-series", "simulation" ]
5983
2
null
5971
1
null
The general approach is to model your latencies in each condition with some distribution, like a Gaussian, and test whether the means of those two distributions are different, e.g. using a [t-test](http://en.wikipedia.org/wiki/Student%27s_t-test). This lets you pick a significance threshold (p-value) and test for it au...
null
CC BY-SA 2.5
null
2011-01-04T19:30:05.887
2011-01-04T19:30:05.887
null
null
2489
null
5984
2
null
1164
5
null
My knowledge of robust estimators is solely in regards to robust standard errors for regression parameters so my comment will only be in regards to those. I would suggest people read this article, On The So-Called "Huber Sandwich Estimator" and "Robust Standard Errors" by: Freedman, A. David The American Statistician, ...
null
CC BY-SA 2.5
null
2011-01-04T19:39:25.350
2011-01-04T19:39:25.350
null
null
1036
null
5985
2
null
5971
1
null
I would take your latency responses from running the operation and perform some tests for normality. If these hold true, then you can create some confidence intervals using a standard normal table. If your tests for normality don't hold true, then a t-table would be more appropriate. You said that you normally plot ...
null
CC BY-SA 2.5
null
2011-01-04T20:03:10.713
2011-01-04T20:03:10.713
null
null
2539
null
5986
2
null
5972
8
null
The estimator is biased, regardless. Note first that $\alpha$ is not identifiable because you cannot distinguish between $\alpha$ and $1-\alpha$. Let's accommodate this problem by allowing that we don't care which coin is which and stipulating (arbitrarily, but with no loss of generality), that $0 \le \alpha \le 1/2...
null
CC BY-SA 2.5
null
2011-01-04T20:23:32.117
2011-01-13T22:10:04.197
2011-01-13T22:10:04.197
919
919
null
5987
1
5989
null
3
779
What is the worst classier that learns badly in practical problems? Edit: Especially bad on test data.. Thanks
Worst classifier
CC BY-SA 2.5
null
2011-01-04T20:58:27.577
2011-01-05T13:27:22.290
2011-01-05T13:27:22.290
2599
2599
[ "machine-learning", "classification" ]
5988
2
null
5918
21
null
The key thing to remember is that for cross-validation to give an (almost) unbiased performance estimate every step involved in fitting the model must also be performed independently in each fold of the cross-validation procedure. The best thing to do is to view feature selection, meta/hyper-parameter setting and opti...
null
CC BY-SA 3.0
null
2011-01-04T21:04:30.177
2014-07-04T20:38:51.437
2014-07-04T20:38:51.437
17230
887
null
5989
2
null
5987
7
null
It is usually the statistician using the classifier that is the problem (for picking the wrong tool for the particular problem at hand, or for using it incorrectly). The "no free lunch" theorems show there is no a-priori distinction between classifiers (which works best/worst depends on the data), so I'd say there isn...
null
CC BY-SA 2.5
null
2011-01-04T21:15:11.963
2011-01-04T21:15:11.963
null
null
887
null
5990
2
null
5987
9
null
Consider the binary case. If you don't know the proportions of the two classes, then the worst you can do is to flip a fair coin in each case: the expected error rate is $1/2$. If you do know the proportions, and the smaller of the two is $p$, say, then you should always classify objects in that category: the expecte...
null
CC BY-SA 2.5
null
2011-01-04T21:17:03.833
2011-01-04T21:17:03.833
null
null
919
null
5991
2
null
5975
7
null
> "Data! Data! Data! I can't make bricks without clay." Sherlock Holmes Sorry, you just can't do it. If you make up some measure that combines some of your variables, then guess what: those exact variables will be predictive of it.
null
CC BY-SA 2.5
null
2011-01-04T22:49:00.363
2011-01-04T22:49:00.363
null
null
279
null
5992
2
null
5962
9
null
The optimal values for the hyper-parameters will be different for different learning taks, you need to tune them separately for every problem. The reason you don't get a single optimum is becuase both the kernel parameter and the regularisation parameter control the complexity of the model. If C is small you get a smo...
null
CC BY-SA 2.5
null
2011-01-05T00:57:32.817
2011-01-05T00:57:32.817
null
null
887
null
5993
2
null
5797
1
null
This answer may be way, way off base as I don't understand the medical context of your question and the nature of the medical test results you allude to, but it might be possible to estimate data mining bias by some sort of Monte Carlo permutation of your results. The type of approach I'm thinking of is taken from a bo...
null
CC BY-SA 2.5
null
2011-01-05T01:32:02.787
2011-01-05T01:32:02.787
null
null
226
null
5995
1
6014
null
3
3420
I apologize in advance for the vague title, but I couldn't think of anything better. I have two datasets, where one is a very small subset of the other. The percentage of people who have a specific attribute in the large dataset is x%. The percentage of people who have the same attribute in the subset is y%. The subset...
Analyzing the difference between two datasets where one is a subset of the other
CC BY-SA 2.5
null
2011-01-05T05:27:36.953
2011-01-05T19:37:25.097
2011-01-05T07:40:00.260
930
null
[ "statistical-significance", "data-mining", "unbiased-estimator" ]
5996
2
null
5982
4
null
Burn-in doesn’t make sense here. The random walk you describe does not have a stationary distribution.
null
CC BY-SA 2.5
null
2011-01-05T05:51:44.557
2011-01-05T05:51:44.557
null
null
1670
null
5997
1
5998
null
11
1095
I'm a beginner to statistics (taken only one college course), but I have a background in programming. I just started playing with a Bayesian classifier library for Ruby and I am looking for ideas for things to analyze. Right now I'm messing around with Tweet categorization, but do you have any ideas? More importantly,...
What kinds of things can I predict with a naive Bayesian classifier?
CC BY-SA 2.5
null
2011-01-05T05:55:56.113
2011-03-26T14:30:20.593
null
null
2649
[ "bayesian", "naive-bayes" ]
5998
2
null
5997
13
null
[The Elements of Statistical Learning](http://www-stat.stanford.edu/~tibs/ElemStatLearn/), by Hastie et al. has a lot of illustrations of Machine Learning applications, and all [data sets](http://www-stat.stanford.edu/~tibs/ElemStatLearn/data.html) are available on the companion website, including data on spam as on th...
null
CC BY-SA 2.5
null
2011-01-05T07:35:46.257
2011-01-05T07:35:46.257
null
null
930
null
5999
2
null
5975
3
null
I agree with @Aniko that you won't be able to "predict" anything without an outcome. Now @Andy suggestion makes sense, provided you find a users database sharing similar characteristics. As an example of related studies, I guess you might find interesting google hits on users' characteristics in studies on Twitter, Fac...
null
CC BY-SA 2.5
null
2011-01-05T10:02:04.577
2011-01-05T10:02:04.577
null
null
930
null
6000
2
null
5995
1
null
For question 2 (significance), could you simply use a randomised resampling procedure and calculate the percentage of subsets of n=500 where the attribute % is ≥60?
null
CC BY-SA 2.5
null
2011-01-05T10:12:10.967
2011-01-05T10:12:10.967
null
null
266
null
6001
2
null
5969
7
null
There were already some useful comments, that are probably waiting for some updates in the question, so I will just drop some general online references: - Practical Data Analysis for the Language Sciences with R, Baayen (2008) - Categorical data analysis: Away from ANOVAs (transformation or not) and towards logit mix...
null
CC BY-SA 2.5
null
2011-01-05T10:55:52.227
2011-01-05T10:55:52.227
null
null
930
null
6002
2
null
5967
4
null
Your dependent variable is growth. For economic time-series data it is more likely that growth will be a stationary process. This means that it will have constant mean. The level data on the other hand is usually non-stationary. Since your model is linear regression you assume that the true data generating process is $...
null
CC BY-SA 2.5
null
2011-01-05T12:06:14.560
2011-01-05T12:06:14.560
null
null
2116
null
6003
2
null
5995
2
null
I interpret "has attribute" as "the value for this attribute is not missing". As you already pointed out, the question now is whether the value "missing" has a importance regarding the target "renewed" (to add another (fictional, but plausible) example: missing entries for attribute "income" in a customer database may ...
null
CC BY-SA 2.5
null
2011-01-05T12:07:25.033
2011-01-05T12:07:25.033
null
null
264
null
6004
2
null
5746
0
null
Also not an answer, but a back-of-the envelope calculation for the simpler case of i.i.d. Xj from a known distribution, to help my (non-statistician's) intuition: Example Monte Carlo, to show the wide variation in run lengths, payoffs and costs: ``` # sample exponential*100 until > the first 3 # c0 = break-even cost, p...
null
CC BY-SA 2.5
null
2011-01-05T12:29:37.580
2011-01-05T12:29:37.580
null
null
557
null
6005
1
6009
null
3
4231
I am slightly new to writing functions in R. Here I have a basic function that searches for a pattern and returns the indexes of where the occurence occurs given a list dataset ``` #this functions takes a pattern and prints the indexes for the matches find_domain <- function(pattern,list) grep(pattern,list,ignore.case...
An R function for performing searches
CC BY-SA 2.5
null
2011-01-05T13:36:36.637
2011-01-05T16:59:03.550
null
null
18462
[ "r", "dataset" ]
6007
2
null
6005
4
null
You should first replace your for loop with something like `apply(d7_dataset, 1, foo)`, where `foo()` is either your function or something along those lines, e.g. `gregexpr()`. The result of `gregexpr()` is a list of numeric vectors with attributes similar to `regexpr()` but giving all matches in each element. On a rel...
null
CC BY-SA 2.5
null
2011-01-05T13:53:05.480
2011-01-05T16:59:03.550
2011-01-05T16:59:03.550
930
930
null
6008
1
6011
null
4
6774
I am trying to do Bayesian posterior predictive checking, whereby I calculate the DIC for my fitted model, and compare to DIC from data simulated from the fitted model. I can get the DIC out of winBUGS, however I am not sure how to calculate the likelihood (for the DIC) outside of winBUGS (i.e., without fitting new mod...
How to calculate likelihood for a bayesian model?
CC BY-SA 2.5
null
2011-01-05T13:56:46.507
2023-04-29T18:48:24.233
2011-01-05T15:59:50.490
930
2654
[ "bayesian", "likelihood" ]
6009
2
null
6005
6
null
If your dataset is a matrix, then `grep` will work directly: ``` > set.seed(1) > bb=matrix(letters[sample(1:20, 100, rep=TRUE)], nrow=20) > grep("b", bb) [1] 10 55 56 69 92 > bb[grep("b", bb)] [1] "b" "b" "b" "b" "b" ``` If you have multiple patterns, then use `ldply` from package [plyr](http://cran.r-project.org/web...
null
CC BY-SA 2.5
null
2011-01-05T14:06:47.837
2011-01-05T14:06:47.837
null
null
2116
null
6011
2
null
6008
4
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The [likelihood](http://en.wikipedia.org/wiki/Likelihood_function) is numerically equal to $\operatorname{P}(D\vert\theta)$, where D is the data vector and theta the parameter vector. Well, strictly speaking it's only equal up to a multiplicative factor, but most software packages including WinBUGS define it as being e...
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CC BY-SA 2.5
null
2011-01-05T15:33:28.930
2011-01-05T16:01:11.860
2011-01-05T16:01:11.860
449
449
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6013
1
6015
null
8
1481
I have a python script that creates a list of lists of server uptime and performance data, where each sub-list (or 'row') contains a particular cluster's stats. For example, nicely formatted it looks something like this: ``` ------- ------------- ------------ ---------- ------------------- Cluster %Availability ...
How to identify outliers in server uptime performance data?
CC BY-SA 4.0
null
2011-01-05T19:17:42.883
2023-01-04T16:08:29.513
2023-01-04T16:08:29.513
362671
2659
[ "outliers", "quantiles" ]