question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>The <code>CircStats</code> toolbox for MATLAB (<a href="http://bit.ly/18C1SCF" rel="nofollow">http://bit.ly/18C1SCF</a>) implements a procedure to compute a correlation between a linear and a circular variable. Specifically, the correlation between a linear variable $x$ and a circular variable $\alpha$ is given by
$... | 72,453 |
<p>I have multiple time series datasets with missing data (the data is missing due to it not being recorded on these dates), and wish to perform a wavelet transformation on the data (probably a MODWT, due to its properties defined by Percival and Walden [2000]). </p>
<p>Given the wavelet details occur at different fre... | 34,396 |
<p>Let $X$ have the pdf $f_X (x;\theta)=1/(2\theta)$ for $-\theta<x<\theta$, zero elsewhere where $\theta>0$ Is the statistic $Y=|X|$ a sufficient statistic for $\theta$?</p>
<hr>
<p>My book claims it is but I do not see it. A transformation argument shows that the distribution of $|X|$ is uniform with $f_X ... | 72,454 |
<p>I'm using <code>cut()</code> to transform data like this:</p>
<pre><code>N <- 10
table(cut(iris$Sepal.Length,quantile(iris$Sepal.Length,probs=seq(0,1,1/N))))
</code></pre>
<p>However, I do have many variables and I would like to determine what is the maximum acceptable <code>N</code> for variable. I thought thi... | 72,455 |
<p>I want to create a bardiagram for these data in R (read from a CVS file):</p>
<p>Experiment_Name MetricA MetricB
Just_X 2 10
Just_X_and_Y 3 20</p>
<p>to have the following diagram:</p>
<p><img src="http://i.stack.imgur.com/kGwFA.png" alt="alt text"></p>
<p>I am beginner and I d... | 72,456 |
<p>I'm working with a biased sample of web users. I'm only able to track responses of users who have navigated my site in a certain way, and I'd like to run an analysis to determine how certain factors (which products they are into, etc) influence how much they buy from my online store.</p>
<p>I've searched around on... | 72,457 |
<p>I have what is possible a naive question. I am current comparing various models (i.e. distributions). And the comparisons do not involve different distributions but rather how the model is fed the data. </p>
<p>For example, two models might be 1) a mixture of a gamma + exponential and 2) a mixture of a gamma + expo... | 72,458 |
<p>I have an astrophysical non-linear curve, specifically a power spectrum. I need to fit this curve with a model and obtain the goodness-of-fit (GOF). This gives me expected and observed values. The data also have observational errors related to instrumental uncertainties. Is there any way I can integrate observationa... | 34,403 |
<p>I have a question about the parameter optimization when I use the 10-fold cross validation.</p>
<p>I want to ask that whether the parameters should fix or not during every fold's model training , i.e. (1) select one set of optimized parameters for every fold's average accuracy.</p>
<p>or</p>
<p>(2) I should find ... | 34,404 |
<p>Could someone please help explain how to calculate $P(A)$ given:</p>
<p>$ P(B) = 0.2 $</p>
<p>$P(A|B) = 0.6$</p>
<p>$P(A|{\rm not} \ B) = 0.6$</p>
<p>Any explaination/help would be greatly appreciated.</p> | 72,459 |
<p>Hello wonderful statisticians, </p>
<p>I'm writing a proposal for a dissertation where I'd like to look at whether heart rate can predict 1) narrative coherence (as judged on a scale - but could also be categorized), and 2) self-reported relationship satisfaction (also scalar). Ideally, I'd also like to see if DV1... | 45,535 |
<p>What are some of the best ranking algorithms with inputs as up and down votes?</p> | 34,409 |
<p>Does anyone know such? I tried to find such procedures in Gretl, but there you can use either hsk procedure for heteroskedasticity correction or ar1 procedure for serial correlation correction. I need the GLS procedure that will deal with both. Thanks </p> | 37,998 |
<p>I want to evaluate the implications of increasing fine prices. I will have a few different scenarios ranging from business as usual, minor increase, proportional increase, categorical increase, to extreme-increases. Each scenario will have different levels of monetary increase depending on the fine details and subpr... | 34,412 |
<p>As far as I know variance is calculated as </p>
<p>$$\text{variance} = \frac{(x-\text{mean})^2}{n}$$</p>
<p>while </p>
<p>$$\text{Empirical Variance} = \frac{(x-\text{mean})^2}{n(n-1)} $$</p>
<p>Is it correct? Or is there some other definition? Kindly explain with example or any refence for reading on this topic... | 34,413 |
<p>I prepared a model which had very good accuracy (80.5%) on my out of sample data. However when I ran that model on a population which is some 6mths old the accuracy went down to abysmal 33%. I am talking here about percentage detection of event (say defaulters). So right now my model is only detecting 33 out of 100 ... | 45,543 |
<p>Running this example from Hyndman's textbook in Chapter 9.1: </p>
<pre><code>auto.arima(austa,d=0,xreg=1:length(austa))
ARIMA(2,0,0) with non-zero mean
Coefficients:
ar1 ar2 intercept 1:length(austa)
1.0371 -0.3379 0.4173 0.1715
s.e. 0.1675 0.1797 0.1866 0.01... | 72,460 |
<p>It is said that to achieve a good result (many different metrics) for text classification, it is not always a business of selecting the algorithm/classifier. Sometimes, it is even more important to find a good feature selection method given the specific task.</p>
<p>However, even before feature selection, selection... | 34,416 |
<p>I am checking stationarity or non-stationarity of a time series with R and I am using <code>adf.test</code> and <code>kpss.test</code> in <code>tseries</code> package. </p>
<p>What are the assumptions for these tests?<br>
Is following a Gaussian distribution by the data set one of the assumption?<br>
If yes, what c... | 34,417 |
<p>I am having trouble understanding the estimation of an AR process. In some textbooks, the AR(1) process is defined as follows: $y_{t}=\theta y_{t-1}+ϵ_t$ (which does not contain a constant). So the OLS estimator is biased. I am confused about the cause of the bias. It is explained that $y_{t-1}$ is dependent on $ϵ_{... | 49,370 |
<p>I am struggeling with this definition the minimum sum of squares for a Matrix $M$:</p>
<p>The minimum value of $f(β)$ where $β = (X′X)^{−1}X′y$ from the system of normal equations $X′Xβ = X′y$ is $$y′(I − X(X′X)^{−1}X′)y = y′My$$,
with $M = (I − X(X′X)^{−1}X′)$ a symmetric, idempotent (T × T)-Matrix.
The trace of ... | 34,419 |
<p>I am not very experienced in statistics that's why you may find my question stupid. Anyway, I want to learn which level of a categorical independent variable should I look to interpret the odd ratios in binary logistic regression. For example, I have one independent categorical variable (education ) with three level... | 72,461 |
<p>I am running an OLS model with a continuous asset index variable as the DV. My data is aggregated from three similar communities in close geographic proximity to one another. Despite this, I thought it important to use community as a controlling variable. As it turns out, community is significant at the 1% level ... | 49,284 |
<p>Is it possible to have multiple (at least 3) dependent variables in a single classification model. I know this can be accomplished in a regression model but I need to perform this with a classification model. </p>
<p>My three DVs are correlated so I do not want to simply write three seperate classification models. ... | 72,462 |
<p>What would be the most efficient way to achieve the following task in R:
combine the values of one variable for those observations which match on one index variable and have specific values on a second index variable.
For example:</p>
<pre><code>id1<-c("a","a","b","b")
id2<-c ("x","y","x","y")
variable<-re... | 72,463 |
<p>I am writing a report on a 2 x 3 mixed study. There is ONE within IV with TWO levels and there is ONE between subjects IV THREE levels. There are two DVs.</p>
<p>Sample sizes for each group is 25, 25, 27.</p>
<p>I tried Mauchly's test but it does not produce any results. I read somewhere that you can only use that... | 72,464 |
<p>This issue seems to rear its ugly head all the time, and I'm trying to decapitate it for my own understanding of statistics (and sanity!). </p>
<p>The assumptions of general linear models (t-test, ANOVA, regression etc.) include the "assumption of normality", but I have found this is rarely described clearly. </p>
... | 49,419 |
<p>How do I use the a priori test to determine a sample size for my prospective cohort research that compares vaccinated males versus non vaccinated males. I am looking at the effect of vaccination on disease prevalence in the future.</p> | 72,465 |
<p>What is the variance of the product of $k$ correlated random variables? </p> | 72,466 |
<p>Here are some results for ANN and KNN on abalone data set using Weka:</p>
<pre><code>Result for ANN
Correctly Classified Instances 3183 76.203 %
Incorrectly Classified Instances 994 23.797 %
Mean absolute error 0.214
Root mean squared error 0.3349
Relative absolute error 58.6486 %
Result for KNN
Corre... | 34,421 |
<p>So in R, for instance, this would be:</p>
<pre><code>my_ts_logged_diffed = diff(log(some_ts_object))
plot(my_ts_logged_diffed)
</code></pre>
<p>This seems to be part of every experienced analyst/forecaster analytical workflow--in particular, a <em>visual examination of the plotted data</em>. What are they looking ... | 72,467 |
<p><strong>We must find the standard deviation out of the text below:</strong></p>
<p><em>The raw material needed for the manufacture of medicine has to be at least $97\%$ pure. A buyer analyzes the nullhypothesis, that the proportion is $\mu_0=97\%$, with the alternative hypothesis that the proportion is higher than ... | 34,422 |
<p>I have a dataset made up of elements from three groups, let's call them G1, G2, and G3.
I analysed certain characteristics of these elements and divided them into 3 types of "behaviour" T1, T2, and T3 (I used cluster analysis to do that).</p>
<p>So, now I have a 3 x 3 contingency table like this with the counts of ... | 34,423 |
<p>In <em>Pattern Recognition and Machine Learning</em> Bishop writes about Bayes networks:</p>
<blockquote>
<p>For practical applications of probabilistic models, it will typically
be the highernumbered variables corresponding to terminal nodes of the
graph that represent the observations, with lower-numbered n... | 72,468 |
<p>As a neuropsychology graduate student with some experience in statistics (I'm usually the guy other psychologists come to with statistics problems <em>after</em> trying it themselves but <em>before</em> seeing a statistician), I am investigating whether a medical treatment has an effect on cognitive measures (aside ... | 44,510 |
<p>I am getting this error in MICE</p>
<pre><code>Error in seq.default(1, ncol(pred)) : 'to' must be of length 1
</code></pre>
<p>My dataset is very large but I have been able to create a reproducible example with smaller subsets, one of which works, and the other of which fails with the above error:</p>
<pre><code>... | 45,568 |
<p>I'm trying to figure out where the false detection rate correction in a genetics paper is coming from and failing. The paper in question is looking at a sequencing method where every sample is read multiple times giving, each time, either a positive or negative result. They're trying to threshold the number of posit... | 38,308 |
<p>People always said that naive Bayes is a linear model. I am not able to understand why, so can anybody explain?</p> | 72,469 |
<p>Do you know NOIR classification of the data? NOIR - nominal ordinal interval ratio. </p>
<p>I want to argue that a line chart can be used with both interval and ratio data whereas area chart should be used only with ratio data.
This is because ratio data has a meaningful 0 and in case of an area chart the baseline ... | 72,470 |
<p>I got some users' history data and generated some sequences of real numbers. The length of each sequence is between 15 and 25. What's more, I do not know whether these sequences have patterns and the frequency is not known as well.</p>
<p>My goal is using each sequence to predict its next value, and then I use auto... | 72,471 |
<p>I have carried a questionnaire, which has a variety of questions in which the responses are given in a rating form (e.g. 1-5, from bad to good). I now would like to test whether the response to question A is affected by several variables, which include some factors (e.g. gender), some continuous (e.g. age) and also ... | 34,427 |
<p>Sorry for asking such stupid question, but I cannot understand the criteria behind contrast matrix, should be created for designing linear models in R. I have read <a href="http://www.bioconductor.org/packages/release/bioc/vignettes/limma/inst/doc/usersguide.pdf" rel="nofollow">limma user guide</a> (P: 101) and ther... | 72,472 |
<p>In some market research consumers are asked to rank the features of a product based on priority. For example,</p>
<p><em>Rank the following features for a device based on your priority (1 being the topmost priority)</em></p>
<pre><code>Storage capacity 6
Portability 5
Touch interface ... | 72,473 |
<p>I have the following toy data:</p>
<pre><code>x <- structure(c(2L, 2L, 3L, 1L, 2L, 3L, 2L, 2L, 2L, 2L, 2L, 2L, 2L,
2L, 3L, 2L, 2L, 2L, 2L, 3L, 2L, 2L, 2L, 2L, 2L, 2L, 3L, 2L, 2L,
2L, 3L, 2L, 2L, 2L, 1L, 2L, 1L, 2L, 2L, 2L, 3L, 2L, 2L, 2L, 2L,
2L, 2L, 2L, 2L, 2L, 1L, 2L, 2L, 2L, 2L, 3L, 3L, 2L, 3L, 2L, 3L,
3L... | 72,474 |
<p>For a general model
$$y_{i} = \alpha + \beta_{1}X_{1} + \beta_{2}X_{2} + \epsilon_{i}$$
regressing $y_{i}$ on $X_{1}$ alone will result in $\beta_{1}$ being biased given by:
$$plim \: \widehat{\beta}_{1} = \beta_{1} + \beta_{2}\frac{Cov(X_{1},X_{2})}{Var(X_{1})}$$</p>
<p>Now I stumbled across a paper which has a mo... | 72,475 |
<p>I'm having difficulty in determining what exactly the difference is between the 2, especially when given an exercise and I have to choose which of the 2 to use. These is how my text book describes them:</p>
<p><strong>Sum standard deviation</strong></p>
<p><em>Given is a population with a normally distributed rand... | 72,476 |
<p>Not sure if this is appropriate for this site, but I'm beginning my MSE in computer science (BS in applied mathematics) and want to get a strong background in machine learning (I'm most likely going to pursue a PhD). One of my sub-interests is neural networks. </p>
<p>What is a good mathematical background for AN... | 72,477 |
<p>How can I approximate a weighted sum of <em>chi</em> distribution? I found several documents for the weighted sum of <strong>chi-squared</strong> distribution and approximation with gamma distribution but I didn't find anything about a weighted sum of <em>chi</em> distributions.</p> | 72,478 |
<p>I have a dataset of paired relations, indicating whether $a$ is in relation with $b$. It is better to consider this dataset as a graph where each node has a numerical value as its feature. Let's say this feature could possibly be varying between $-10$ and $10$. Now the question is: Are two nodes related one to each ... | 18,450 |
<p>When I'm coding a Monte Carlo simulation for some problem, and the model is simple enough, I use a very basic textbook Gibbs sampling. When it's not possible to use Gibbs sampling, I code the textbook Metropolis-Hastings I've learned years ago. The only thought I give to it is choosing the jumping distribution or it... | 72,479 |
<p>In case of the ordinal logistic regression, both of the goodness-of-fit statistics, Pearson and Deviance goodness-of-fit measures, should be used only for models that have reasonably large expected values in each cell. If you have a continuous independent variable or many categorical predictors or some predictors wi... | 38,420 |
<p>I am not a statistician so apologies if my terminology is wrong</p>
<p>I have a dataset of >14 million p values derived from Fisher's exact testing on genome scale sequencing data.</p>
<p>Benjamini-Hochberg correction of these p-values turns out only ~1500 significant p-values so I have been attempting to use qval... | 72,480 |
<p>I was reading this article in wikipedia related to MAP <a href="http://en.wikipedia.org/wiki/Maximum_a_posteriori_estimation" rel="nofollow">http://en.wikipedia.org/wiki/Maximum_a_posteriori_estimation</a>. However, I had this confusion when it says</p>
<p>MAP estimation is a limit of Bayes estimators (under the 0-... | 72,481 |
<p>I have an argument with my advisor over data visualization.
He claims that when representing experimental results, the values should be plotted with "<em>markers</em>" only, as presented in the image bellow. While curves should only represent a "<strong>model</strong>"</p>
<p><img src="https://dl.dropbox.com/u/6484... | 72,482 |
<p>Given the following model which relates the full year home sales to the unemployment rate (observed or estimated) I get a projected increase of 14% for 2013 over 2012... last year the same approach over projected by 6% (the 2012 projection was for 41,992 and the actual is coming in about 39,535) So I think the model... | 72,483 |
<p>I have a data set with approximately 500 observations on eight key variables. There are a lot of missing data; only about 1/12 of the observations are complete. I am using <code>PROC MI</code> and <code>MIANALYZE</code> in SAS to run various regressions on multiply imputed data, and this is working well. (There are... | 72,484 |
<p>I found excellent notes on ARCH and GARCH models <a href="http://public.econ.duke.edu/~boller/Econ.350/talk_garch_11.pdf" rel="nofollow">here</a>. On page 3 it is given that: </p>
<p>Standard time series models:</p>
<p>\begin{eqnarray*}
Y_{t} & = & E\left(Y_{t}|\Omega_{t-1}\right)+\epsilon_{t}\\
E\left(Y_{... | 72,485 |
<p>I have 2 data sets. The first data set, let's call it $X$ has an average value of ($\bar X$) and standard deviation of ($STD_X$), the second set of data also has the average value of ($\bar Y$) and standard deviation of ($STD_Y$). I want to find out the standard error or standard deviation of a percentage change of ... | 49,796 |
<p>With all the media talk and hype about deep learning these days, I read some elementary stuff about it. I just found that it is just another machine learning method to learn patterns from data. But my question is: where does and why this method shine? Why all the talk about it right now? I.e. what is the fuss all ab... | 34,436 |
<p>In my self-study, I have read the wikipedia entries and some books in regards to M-estimators and L-estimators.</p>
<p>I understand that M-estimators are so called "M" because they "Maximize" the likelihood function, and/or functions of the data itself. I also understand that L-estimators are so called because they... | 72,486 |
<p>I'm trying to perform a markov switching regression model in stata using the command <em>switchr</em>.</p>
<p>The command syntax is the following one:</p>
<p><em>switchr eq1 eq2 [weight] [if exp] [, cluster(string) strata(string) sigequal tol(real) tout(integer) noisyn(integer) ]</em></p>
<p>where <em>eq1</em> an... | 72,487 |
<p>Is there any statistical test or measure to evaluation the degree of correlation or dependence between two sets of data-points ?</p> | 38,006 |
<p>I have a hierarchical feature matrix, By that I mean that each item may belongs to one or more category, so my data will look something like that </p>
|  User | 
Categ  |
Item  |<br>
|  1 | 12  | 120&nbs... | 72,488 |
<p>I have a number of parameters for a model. The parameter values are presented as the mean and the 95% confidence interval. I am not provided with standard deviation or sample size. </p>
<p>I am using R. I would like to sample an estimate for each parameter, similarly to using
rnorm(n, mean, sd) to draw from a norm... | 49,898 |
<p>I have a set of data points and I was told that for it to be valid, every data point should be within +/- say 5% of the average of the entire dataset.</p>
<p>I have no problem of checking each data point and reach a conclusion if it is valid. My question is, how can I relate above statement to a statistic measure s... | 72,489 |
<p>I have wood density data for a number of tree species given a tree's state of decay. I am presented with mean density and standard errors (SE). I am NOT provided with sample sizes.</p>
<p>For example, a decay class 1 fir tree has a mean density of 0.305 with a standard error of 0.024.</p>
<p>I am using R. I wo... | 49,898 |
<p>I am wondering whether someone has a tip on this potentially very basic question. i have done some grid-based bayesian analysis and ended up with a non-standard discrete posterior density function over an interval of 100 observational values (per graph) below and as shown in the vector format per below. I can easily... | 72,490 |
<p>Is there a prior that's commonly used for "index" or "score" type variables that are user-defined as a weighted sum of a small number of variables (sometimes with pre-defined interaction contributions)? </p>
<p>I know the gamma, inverse gamma, binomial, negative binomial, poisson, etc distributions are strictly pos... | 72,491 |
<p>I've been assigned to do a cross-class project between political science and math about the behavior of voters in a democratic state. More specifically, I'm focusing on a party from a national election in 2007, where I have made a table consisting of two rows – mandates and news about that party – and one column for... | 49,008 |
<p>I have some data that looks like this:</p>
<pre><code>Prob Outcome
0.09 0
0.10 0
0.10 0
0.11 1
0.84 1
0.99 1
0.86 1
0.78 1
0.86 1
0.00 0
etc.
</code></pre>
<p>i.e. a bunch a probabilities each with a single test. What statisitcal test should I use to test the hypothesis that the pr... | 47,923 |
<p>I'm currently facing a problem in which some of my training examples belong to more than one class at the same time, say, sample $y_i$ pertains to class $A$ and $B$. I was thinking that a solution to it would be to consider that sample as two-fold, i.e., consider it as two samples, one for class $A$ and one for clas... | 19,446 |
<p>Suppose we wish to model two variables $x$ and $y$, as having an underlying linear relation with added errors. That is, with data $(x,y)_i: i = 1,...,n$, we model:
$$
\begin{pmatrix} x_i \\ y_i \end{pmatrix} \sim \mathcal N\left(\begin{pmatrix}u_i\\v_i\end{pmatrix},\Sigma\right)
$$
and $v_i = a + bu_i$ with some pa... | 34,444 |
<p>Possible <a href="http://stats.stackexchange.com/questions/8130/sample-size-required-to-determine-which-of-a-set-of-advertisements-has-the-highes">Duplicate</a></p>
<p>First, I am not a statistician (though I'd like be one) but I am trying to understand how different tests can be utilized to examine samples.</p>
<... | 34,445 |
<p>In the context of likelihood-based inference, I've seen some notation concerning the parameter(s) of interest which I've found a little confusing. </p>
<p>For example, notation such as $p_{\theta}(x)$ and ${\mathbb E}_{\theta}\left[S(\theta)\right]$.</p>
<p>What is the significance of the parameter ($\theta$) in s... | 37,193 |
<p>I have a set of $n$ events. Each event has $m$ variables. At least 1 event produces an observation. It is possible for several events to occur simultaneously.</p>
<p>E.g.</p>
<p>4 Events. 3 variables each:</p>
<p>$E_{11}=0.4, E_{12}=-0.3, E_{13}=-0.4, E_{21}=0.3, ... , E_{42}=-3.0, E_{43}=2.1$<br>
produces $y_1 =... | 72,492 |
<p>A researcher knows that the probability that a questionnaire will be reponded by mail is 40%.
He wants to be 99% sure he will get at least 200 responded questionnaires back.
How many questionnaires must he send by mail to be 99% sure he will get at least 200 answers?</p> | 72,493 |
<p>I'm measuring error on the median of my data using bootstrapping. I would like to obtain I sigma error bars on my data, so I'm measuring the 16th and 84th percentiles of my data. Should I divide these percentile values by the square root of the number of data or not?
Thanks in advance.</p> | 72,494 |
<p>How can you prove that the normal equations: $(X^TX)\beta = X^TY$ have one or more solutions without the assumption that X is invertible?</p>
<p>My only guess is that it has something to do with generalized inverse, but I am totally lost.</p> | 49,667 |
<p>Im just wondering .. Everywhere I see only tables with the Qcritic as the results. Lets say I have a big set of data samples (like 1000 or more). Is then a way of mathematically calculate a Qcritic value? Is there any mathematical formula for Qcritic?</p> | 34,450 |
<p>I am trying to fit a MIMIC model measuring poverty in a household sample. The model looks like this: (HUMCAP -> education job) (HOUSINGQUAL -> floor wall dwelling tv refrigerator radio electricity lighting heating cooking washingmachine) (POV->HUMCAP HOUSINGQUAL)</p>
<p>However, when trying to fit this model it ite... | 2,098 |
<p>Suppose that I am concerned with objects that are described by N 2D points. These points all have equal importance to me. I begin with a large number R of such objects, each with its corresponding N-element list of 2D points. Let's call this the population. </p>
<p>I'm now given a new object B, with the N locations... | 34,452 |
<p>I have two sets of mean data that I have done a Kolmogorov-Smirnov test on. The tests came back showing that one data set was normal, but the other was not. The two data sets are independent of each other, and I need to compare the differences in the mean. </p>
<p>The fact that one of the data sets isn't normal sur... | 72,495 |
<p>I have a 3-category ordered outcome (food consumption: 1=no food, 2=less food, 3=more food) and a 3-category ordered predictor (food exposure: 3=no time, 2= less time, 1= more time- whereby 3=no time is taken as reference category in the ordinal regression model). I want to explore hypothesis that more food exposur... | 34,453 |
<p>I have 4 sets of random floats between [0,1]: $d1, d2, d3, d4$. I need to compare these sets by pairs and I make use of the <code>kde.test</code> function of R's <a href="http://cran.r-project.org/web/packages/ks/ks.pdf" rel="nofollow"><code>ks</code> package</a> to do so.</p>
<p>When I use <code>kde.test</code> to... | 19,494 |
<p>I understand, that the basic model of simple linear regression assumes homoscedasticity, i.e. the variances $\sigma^2$ around the regression line are equal for all predictor levels/values. </p>
<p>With this assumption in mind, I wonder why confidence intervals for a predicted $y$ value are not equally large for all... | 72,496 |
<p>Suppose I have a covariance (error) matrix <code>C_xyz</code> for system with 3 parameters: <code>x, y, z</code>.</p>
<p>Then it appears that <code>x, y</code> and <code>z</code> depends on each other: </p>
<pre><code>det(C_xyz) = 0
ax + by + z = 0
</code></pre>
<p>How to find covariance matrix <code>C_xy</code> ... | 72,497 |
<p>I am still confused in using Cronbach's Alpha. Do we have to use it in sample survey before going for final survey? or is value of Alpha calculated based on the final survey data? Similarly, what does the set of questions measuring a construct mean? Does it mean that the questions are mutually exclusive or do all th... | 72,498 |
<p>I'm running an example of Smooth Transition AR (STAR) Model from the book "Analysis of financial time series, 3rd edition" by Tsay, in section 4.1.3. The script is as follows:</p>
<pre><code>da=read.table("data/m-3m4608.txt",header=T)
rtn=da[,2]
star <- function(par){
f = 0
T1=length(rtn)
h=c(1,1)
at=c(0,0)
for ... | 72,499 |
<p>I have data of size 116.667 rows defined as:</p>
<pre><code>iD Signal
chr17.3620 0.5741552
chr1.7341 0.5680284
chr7.3937 0.5479430
chr17.3890 0.5402434
chr12.3200 0.5298978
chr17.7227 0.5298536
</code></pre>
<p>As it is difficult to show results with all the data, because I have no reputation enough to up... | 72,500 |
<p>What free tool can I use to do simple Monte Carlo simulations on OS X?</p> | 72,501 |
<p>Greetings,
I am working on joint and conditional density trees for approximating clique potentials in Bayesian Belief Networks. A brief introduction to topic is available from this paper: <a href="http://www.autonlab.org/autonweb/14653.html" rel="nofollow">http://www.autonlab.org/autonweb/14653.html</a> in case you... | 72,502 |
<p>I am new to this forum but have found several threads to be highly useful so am posing a question myself.</p>
<p>My data was collected (<strong>fish length = factor</strong>, <strong>fish mercury = response</strong>) from several rivers over several years for the purpose of environmental (mercury) monitoring. </p>
... | 72,503 |
<p>I have included a diagram of an experiment where cells are pooled from multiple animals, cells from the pool are then allocated to different treatments and a measurement is taken from each individual cell in each treatment. The aim of this experiment is to determine how doses of a drug (treatments) affect cell size.... | 72,504 |
<p>In Excel's data mining tools there is a "Key Influencers" tool which will look at a dataset which is perhaps customers and whether or not they converted to a given goal (e.g. a flag that equals 1). It then tells you the most influential factors in reaching that goal,( e.g. Gender=Male and Age=30-45). What would be e... | 72,505 |
<p>I'm trying to fit a line into a graph with points that have errors both in the y and x directions. I found the following document on the subject:</p>
<p><a href="https://www.che.udel.edu/pdf/FittingData.pdf" rel="nofollow">https://www.che.udel.edu/pdf/FittingData.pdf</a></p>
<p>My problem is that I don't quite und... | 72,506 |
<p>I am curious, is there a way to optimize a regression according to a specific statistic? </p>
<p>Let's say I am interested in a model with the best possible AIC statistic (or MSE or whatever measurement I am interested in) - could I somehow direct the regression to give me the top X models that would do this? (Of c... | 196 |
<p>When splitting up my labeled data into training, validation and test sets, I have heard everything from 50/25/25 to 85/5/10. I am sure this depends on how you are going to use your model and how prone to overfitting your learning algorithm is. Is there a way to decide or is it all by rule of thumb? Even ELSII see... | 34,460 |
<p>I realise this is probably a very simple question but after searching I can't find the answer I am looking for.</p>
<p>I have a problem where I need to standardize the variables run the (ridge regression) to calculate the ridge estimates of the betas. </p>
<p>I then need to convert these back to the original varia... | 49,927 |
<p>I have problem understanding following example in parentheses. Maybe you can help me.</p>
<p>Ideally, researchers know the full extent of the population they want to study, and they can select a sample from this population at random. Statisticians can calculate the probability that such random samples represent the... | 72,507 |
<p>In SAS Enterprise Miner 6.2 it's possible to approximate CHAID and CART methods using Decision Tree node, according to SAS Help, but there is nothing about C4.5 algorithm.</p>
<p>How can I mimic C4.5 algorithm using Decision Tree node?</p>
<p>I would be grateful for any help. </p> | 34,462 |
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