question stringlengths 37 38.8k | group_id int64 0 74.5k |
|---|---|
<p>Suppose that I have a new way of estimating covariance matrice (from a particular data set), and that I believe this is better than the sample covariance matrix. I want to fit a t-copula with this new covariance matrix, and assess how good this particular choice of copula and covariance matrix (vs. say the gaussian ... | 72,912 |
<p>I am exploring the psychometric properties of a 10-item self-report measure. I have about 400 cases in two independent samples. The items are completed on 4-point Likert scales. An EFA clearly supports a one-factor solution (e.g., first eigenvalue over 6, all others under 1) and Cronbach's alpha is good (e.g., .90).... | 72,913 |
<p>The following table represents the relative frequency of accidents per day in a city. </p>
<pre><code>Number of accidents Relative frequency
0 0.55
1 0.20
2 0.10
3 0.15
4 or more 0.00
</code></pre>
<p>Which of the followi... | 72,914 |
<p>I am working on binary classification problem. Data set is very large and highly imbalanced.<br>
Data dimensionality is also very high.
Now I want to balance data by under-sampling the majority class, and I also want to reduce data dimensionality by applying PCA, etc... </p>
<p>So my question is that which one shou... | 72,915 |
<p>If a 95% confidence interval for a population mean ranges from 200 to 240 (that is, LCL=200 and UCL=240). Then, the computed numerical values of sample mean, $\bar{x}$, and sample standard deviation must have been:</p>
<p>a) we cannot tell from the given information</p>
<p>b) $\bar{x}$ = 220 and s=20</p>
<p>c) $\... | 72,916 |
<p>I have been doing some research on constrained models and have recently read the paper:</p>
<blockquote>
<p>Gunn and Dunson (2005) "A Transformation Approach for Incorporating
Monotone or Unimodel Constraints", Biostatistics, 6, 434-449</p>
</blockquote>
<p>In this paper they advocate fitting an unconstrained ... | 46,337 |
<p>I have four datasets: D1, D2, D3 and D4. Each dataset contains elements (<strong><em>different sample size in each dataset</em></strong>) that can be described by 100 categories (1 represents that the element belongs to that category and 0 represents otherwise). So for example,</p>
<pre><code>D1
Element Categor... | 35,055 |
<p>I have some data which looks from plotting a graph of residuals vs time almost normal but I want to be sure. How can I test for normality of error residuals?</p> | 72,917 |
<p>Ljung Box test tells that the following time series is white noise (<code>p=0.9746845</code> for the current run). How could this be?</p>
<pre><code>x=rep(10,1000)
x[500]=-10
Box.test(x,type="Ljung-Box")$p.value
</code></pre>
<p><img src="http://i.stack.imgur.com/6VSlm.jpg" alt="The time series"></p> | 72,918 |
<p>Does anyone know how to create a scatterplot in R to create plots like these in PRISM's graphpad:</p>
<p><a href="http://graphpad.com/support/faq/graph-tip-how-can-i-make-a-barcolumn-graph-that-also-shows-the-individual-data-points/" rel="nofollow">http://graphpad.com/support/faq/graph-tip-how-can-i-make-a-barcolum... | 72,919 |
<p>Can you suggest some pointers on how I can manipulate my data to be 'smoother'? Any algorithms, or techniques that would be useful in this aspect?</p>
<hr>
<p>Updates:</p>
<p>In response to the comments asking for more info:</p>
<ul>
<li><p>The data does not follow a known distribution as far as I know.</p></li>... | 72,920 |
<p>I am not very well knowledgeable in statistics as I have yet to take a formal class in it (but have signed up for one next year) and yet find myself in need of finding out whether or not a single data point in a list of values is statistically significant. My data is a list of 4000 values (a power spectrum to be exa... | 35,060 |
<p>I am using ROC curves and full AUC values to compare different models, using simulated data. Now I think I am confused with the interpretations of ROC curves and AUC values. Please see the figure below (sorry it is partial from screen shots...)</p>
<p>There are three models compared, and I know that the model shown... | 72,921 |
<p>Let's assume we have a discrete binary random variable K (K=0 or K=1) for which the prior distribution is binomial. My understanding of Bayesian statistics tells me that regardless of the likelihood, the posterior distribution for K can only be binomial as well. However, I have encountered a text which talks about "... | 72,922 |
<p>Are there any standard algorithms for keyphrase clustering. There are several algorithms for keyphrase extraction from a corpus. For e.g. <a href="http://aclweb.org/anthology/C/C10/C10-2042.pdf" rel="nofollow">this publication</a> reviews some of the popular keyphrase extraction algorithms. Example of possible keyph... | 35,065 |
<p>I have centered and scaled inputs via <code>prcomp ()</code>:</p>
<pre><code>prOut<-prcomp(trainSet[,2:4],scale = TRUE,scores=TRUE)
</code></pre>
<p>I now want to use my completed model on new (future) data.
I assume the correct approach is to use the training data <code>prOut$scale</code> and <code>prOut$cente... | 72,923 |
<p>Suppose we have 4 groups of animals (pig, dog, rabbit, cat). There are 10 animals in each group. We measure the weight and pulse of each animal.</p>
<p><img src="http://i.stack.imgur.com/0ramF.jpg" alt="enter image description here"></p>
<p>Consider the following procedure in SAS:</p>
<pre><code>proc discrim data... | 35,069 |
<p>I am using sequential filtering framework to estimate the average speeds on different freeway segments from spot speeds obtained from multiple vehicles.</p>
<p>Consider a mile-long stretch of a freeway, and a 2-minutes interval. I get speed measurements from $n$ vehicles (from an app like Waze) on this segment duri... | 72,924 |
<p>Consider a mixture of two normal distributions:
$ f(x) = p N(x|u_1, S_1) + (1-p) N(x|u_2, S_2) $ where
N() is the normal pdf. $p$, $S_2$, and $S_2$ are known. The means are not.</p>
<p>You can get the MLE of $u_1$ and $u_2$ from the EM algorithm.</p>
<p>My question is, for a sample of size n, what are the varian... | 72,925 |
<p>One of the steps in Expectation Propagation based inferencing is to be able to divide out a factor which has a normal form from the current posterior distribution (which is a high dimensional Gaussian). The idea is that the division removes the influence of that factor from the posterior distribution.</p>
<p>So, as... | 72,926 |
<p>Here we have a arrival process. The inter-arrival time follows a shifted negative exponential distribution. The density function of the distribution is:</p>
<p>$$f(t)=\lambda e^{-\lambda(t-\theta)},\quad\text{ where }t\ge\theta$$</p>
<p>How to derive the variance of the number of arrivals in time period of $T$?</p... | 72,927 |
<p>I calculated the dispersion parameters for each of two blocks in a hierarchical logistic regression. I am not quite sure how to interpret the dispersion parameter. </p>
<p>First I calculated the parameters by taking the chi-square goodness-of-fit statistic (hosmer-lemeshow-test) and dividing it by the degrees of fr... | 35,076 |
<p>My dependent variable is mostly continuous and positive, but has a modest number of zeros (10% of the sample). The results from tobit and ols are very similar. How can I formally compare the tobit and ols results? I think that I should be using ols, because tobit doesn't change anything.</p> | 72,928 |
<p>I have a data-table that has about 26000 rows and about 35 columns. The columns are paired, so the values in columns 6 and 7 (for example) are related to each other, so are 8 and 9 and so on. There are 23 different types of annotations in the table, which I have read in as "factor". The ratio of these pairs of co... | 72,929 |
<p>After development of recommendation engine with the R, before removal of outliers from data-set value of residual standard error was 1351 and after removal of outlier its 656. Still there is no accurate prediction which gives 10% correct(near) prediction. For more fitting i also have tried polynomial model with two ... | 72,930 |
<p>correct me if I'm wrong, I've read that my sample should be normally distributed if I'm going to use moderation analysis. But if in case I'll be using purposive sampling (I'm following certain criteria / conditions )what can I do as a solution in the problem of normal distribution? my last question will be, is moder... | 72,931 |
<p>I have a small issue regarding first difference models. Suppose we have</p>
<p>$$ \Delta y_{t} = \beta_{0} + \beta_{1} \Delta \log{y_{t-1}} + \Delta u_{t} $$</p>
<p>The interpretation of the delta would be the same as if I did with:</p>
<p>$$ y_{t} = \beta_{0} + \beta_{1} \log{y_{t-1}} + u_{t} $$</p>
<p>That is ... | 72,932 |
<p>$$
f_{X}(x) = \frac{3}{8}(x+1)^{2} ,\ -1 < x < 1
$$</p>
<p>$$Y = \begin{cases} 1 - X^{2} & X \leq 0,\\
1- X, & X > 0.\end{cases}$$</p>
<p>I started with :
$$
F_{Y}(y) = 1 - P(Y \leq y)
$$
$$
= 1 - [P(-(1-y)^\frac {1}{2} < X < (1-y)]
$$</p>
<p>From here, I can get $F_{Y}(y)$, and ... | 35,084 |
<p>I have two dummy variables, X1 and X2. Each one is coded into 0 or 1. Here is the breakdown:</p>
<pre><code> alcohol use
X7 X8
none 0 0
moderate 1 0
severe 0 1
</code></pre>
<p>I don't understand how to tell SPSS that when X7 is 0, AND X8 is 1, that means 'Severe'. The probl... | 72,933 |
<p>I am using RandomForest regressor on my data and I could see that the oob score was obtained to be 0.83. I am not sure how it came out to be like this. I mean my targets are high values in the range of 10^7. So if it's MSE then it should have been much higher. I don't understand what 0.83 signify here.</p>
<p>I am ... | 72,934 |
<p>I am trying to learn R programming and I am having trouble with a problem. I am trying to set a probability of success $p$ and find out what the chance of success is for $n$ trials. Basically a Bernoulli trial but I am trying to implement it myself using a <code>while</code> loop to learn R better.</p>
<p>I know th... | 35,086 |
<p>In many scientific fields, a p value less than 0.05 is considered significant, pointing to real difference in reality, whereas anything above it cannot be accepted (i.e. null hypothesis cannot be rejected, which means your results cannot be accepted for publication),
From a perspective of pure statistics, this thres... | 49,911 |
<p>I have run a sequence of nested multi-level models using lmer, and looked at both the summary output giving all the coefficients, etc, as well as the Anova output which does a chi-squared test on each of the factors. </p>
<p>In the first model without the interaction, the factor medium is significant, looking at b... | 72,935 |
<p>So I am working on a new project looking at formal and informal networks between businesses in the same industry. Namely, I am looking at joint ventures, fractional acquisitions, minority share ownership, and board of director relationships between companies. I want to see if I can identify the occurrences of "weak ... | 72,936 |
<p>Is there a statistical reason why item analysis/response theory isn't more widely applied? For instance, if a teacher gives a 25 question multiple choice test and finds that 10 questions were answered correctly by everyone, 10 questions were answered by a really low fraction (say 10%) and the remaining 5 were answer... | 72,937 |
<p>I have fit a probit model in R. However, in addition to the $z$- and $p$-values, I would like to know the Wald $\chi^2$ values for the individual explanatory variables. How do I obtain / calculate the Wald $\chi^2$ values for parameter estimates?</p> | 72,938 |
<p>Say we have N voters from some group (N binomial variables). Each voter has a preference on voting about some issue (probability of "success" p), which depends on the preferences of other voters.</p>
<p>Given a sample of votes for each voter (an estimation of their preference on that issue), and an estimation of t... | 35,097 |
<p>Consider Jaynes' solution to the <a href="http://en.wikipedia.org/wiki/Bertrand_paradox_%28probability%29">Bertrand paradox</a> using the <a href="http://bayes.wustl.edu/etj/articles/well.pdf">principle of indifference</a>. Why doesn't a similar argument apply to the <a href="http://en.wikipedia.org/wiki/Borel%E2%80... | 72,939 |
<p>I'm new proportional hazard ratio models and new-ish to R, so I suspect this is a basic question:</p>
<p>The scenario is modeling the speed of an effect through hazard ratios. People are joining an organization, and most are invited by someone else within the organization*. The speed measured is the time between wh... | 72,940 |
<p>I am using a GAM in R to compare time series data from 3 countries. The data sets are of hourly measurements for one year. The main aim here is to show when at which time of the day and day of the year are the data well matched to the mean series. The script below shows my attempt:</p>
<pre><code>## Ozone measureme... | 72,941 |
<p>I have 21 socio-economic and attitudinal macro-level variables (such as percentage of mothers aged 24-54 not employed, percentage of children aged 3-5 in nursery schools and so on). I also have data on the proportions of grandparents which provided intensive childcare. Most of the socio-economic variables which I se... | 37,816 |
<p>Consider the context of a dendrogram clustering. Let us call <em>original dissimilarities</em> the distances between the individuals. After constructing the dendrogram we define the <em>cophenetic dissimilarity</em> between two individuals as the distance between the clusters to which these individuals belong. </p>... | 35,099 |
<p>I'm dealing with a supervised binary classification issue. I'd like to use the GBM package to classify individuals as uninfected/infected. I have 15 times more uninfected than infected individuals.</p>
<p>I was wondering if GBM models suffer in the case of imbalanced class sizes? I didn't find any references answer... | 72,942 |
<p>I'm perplexed by some vertical lines that show up in these scatter plots on a log scale. Population is on the y-axis and the proportion of the neighborhood with the attribute mentioned in the panel label on the x-axis. Is this just an artifact of the transformation? (I thought perhaps this was due to digit preferenc... | 49,912 |
<p>I have a question about the support vector machine (SVM) kernel trick. How do you find the boundaries of the training data set in kernel projected space? Is that the same boundaries as you can obtain in original input space? Does kernel mapping change the data distribution? I am new to SVM, can someone please give ... | 72,943 |
<p>I'm modeling a Bayes net with OpenBUGS, and I find problems to specify some of the parameters and their priors. </p>
<p>The aim of the model is to identify latent groups in the data from a sample of human participants. Eventually, I need a belief distribution over the range of 5 possible latent groups, for each ind... | 72,944 |
<p>I am interested in how uncertainty can be accounted for when considering the risk of extinction of a species. Forgive me for extending a rather tired thought experiment, but at least it's familiar territory and I hope it illustrates what I am trying to understand.</p>
<p>Let's say that Schrödinger was not satisfied... | 49,915 |
<p>I am interested in modelling the impact of some environmental parameters on a concentration of measured phytoplankton pigment. The concentration of pigment is skewed so that low concentrations are more frequent than high ones and there are occasions of 0 (zero) concentration. I was hoping to use a GLM model with a G... | 35,101 |
<p>I am analyzing my data on the relationship between spirituality and negative emotional states (depression, anxiety, and stress) using a hierarchical multiple linear regression. Everything seemed to be "okay" with the results until I checked the signs of the regression coefficients!! The results are showing a positiv... | 72,945 |
<p>I would like to know if there's a way to build a classification model
in R that would allow me to change the class weights at prediction
time. </p>
<p>The scenario where I would want to do this:</p>
<p>I have a group of products, that are one of three different types
(A, B, and C). The types occur in in observed... | 72,946 |
<p>Let $H$~$\mathcal{N}(\mu_H,{\sigma_H}^2)$ and $S$~$\mathcal{N}(\mu_S,{\sigma_S}^2)$.
$H$ and $S$ are dependent of each other and their covariances are unknown. </p>
<p>Let $G = H - S$ and the mean and variance of $G$~$\mathcal{N}(\mu_G,{\sigma_G}^2)$ are known. </p>
<p>Is there a way to I estimate the multivariat... | 20,640 |
<p>I have data that have been aggregated with unknown variance into a number of composite averages. These data are generated from pooled assays, such as HIV viral load in a composite of 10 vials of blood, or cystic fibrosis protein concentration in a composite of 10 0.01cc biopsies of lung tissue. We have treated and c... | 72,947 |
<p>I am trying to quantify my concerns regarding a proposed incinerator in our community. The company is basing its potential to emit dioxins (a class of chlorinated organic compounds with a reference dose of 1.7E-8 grams per 150 lb person per year) on three emission measurements (mg/m^3 exhaust): </p>
<p>0.0002139;
... | 35,103 |
<p>I am comparing 2 different data sets. I have broken down each set into quartiles. I am looking at the percentage of increase between the quartiles (example there was a 125 percent increase between the 2nd and 3rd quartile for one data set and a 123 percent increase between the 2nd and 3rd increase of the other dat... | 72,948 |
<p>I am using two different methods to obtain the frequency of several events. Can I use a scatter plot to graph the frequency of an event obtained by Method A against the one obtained by Method B? And afterwards, report the correlation coefficient to state that, since they strongly correlate, they can be used interc... | 72,949 |
<p>I am developing model-based clustering. </p>
<p>First, I developed model-based clustering in R using "mclust." Next, I wanted to take 75% of the sample, re-run model-based clustering and compare the results with the results from the entire dataset using variation of information or rand index. However, I am getti... | 72,950 |
<p>For some time, I wanted to stop copy-pasting my R results into word, but climbing the LaTex mountain seemed to much to be worth it. Recently, I came to discover LyX, as a laymen's solution to people like me who do not wish to code their text, but do wish to combine R analysis with text.</p>
<p>However, I found the... | 38,059 |
<p>I had measured the association between two categorical variables some time back. Now, I have even more data compared to the last time. I find that the Cramér's <em>V</em> values has decreased now. </p>
<p>Is this because of the increase in the number of data points? </p>
<p>Can we at all attribute this change in C... | 72,951 |
<p>My understanding is that with an odds ratio (OR) that a 95% CI containing 1 means that there is no difference between the odds of something occurring between groups. I wondered if this holds true for incident rate ratios (IRR)?</p>
<p>Many thanks,
Ewen</p> | 35,105 |
<p>I'm reading a data mining book and it mentioned the Kappa statistic as a mean for evaluating the predication performance of classifiers. However I just can't understand this. I also checked wikipedia but it didn't help too. </p>
<p>How does Kappa help in evaluating the predication performance of classifiers? What d... | 24,895 |
<p><strong>General description of the problem</strong></p>
<p>There is a graph where some of the nodes have a certain type(There are about 3-4 types). For other nodes, type is not known.
I want to predict, based on my graph, for the nodes with unknown type their "most probable" type.</p>
<p><strong>Possible framework... | 30,719 |
<p>I'm looking for papers or other examples of research where the statistical analysis done would be within the grasp of someone who has done an introductory stats course. Ideally the datasets would also be available online.</p>
<p>The idea is to pass these to students and examples they can follow and reproduce.</p> | 72,952 |
<p>I'm doing a linear mixed effects analysis in which I'm really only interested in one of the fixed effects. I have several other fixed effects and a random intercept term, but none of them are relevant, nor is the overall goodness-of-fit of the model (other than the fact that adding my regressor of interest (ROI) imp... | 72,953 |
<p>Can I multiply impute missing data in some of the
variables which were for some reason not measured at one time? </p>
<p>For
instance, for production I have time series data for 1961-2011: however, some of<br>
the predictor variables (rainfall, temperature, humidity and few more) which
I suspect could have impac... | 35,109 |
<p>Since regression modeling is often more "art" than science, I often find myself testing many iterations of a regression structure. What are some efficient ways to summarize the information from these multiple model runs in an attempt to find the "best" model? One approach I've used is to put all the models into a li... | 35,110 |
<p>Suppose $c>0,\sigma>0$ and $\tau>0$ are fixed real constants. Then I'd like to prove that the function $g_c:(-1,1)\mapsto\mathbb{R}$
defined by
\begin{equation}
g_c(\rho)=\int_{-\infty}^\infty\int_{-\infty}^\infty\frac{ \{(-c)\vee x \wedge c\} \{(-c)\vee y \wedge c\}}{\sqrt{2\pi(1-\rho^2)}\sigma\tau}
e^... | 72,954 |
<p>Can the KS3D2 test as suggested by <a href="http://adsabs.harvard.edu/abs/1987MNRAS.225..155F" rel="nofollow">Fasano and Franceschini (1987)</a> be used when one of the three variables take discrete values between 0-40? The other two variables are continuous. </p> | 46,405 |
<p>Is it true that if a random variable $$X$$ follows a distribution, say one of these</p>
<ul>
<li>Binomial</li>
<li>Poisson</li>
<li>Exponential</li>
<li>Normal</li>
<li>Uniform</li>
</ul>
<p>Then $$\frac{X}{20}$$</p>
<p>follows the very same distribution as $X$?</p> | 35,112 |
<p>We know that</p>
<p>$X$ follows $\mathrm{Bin}(n_1,p_1)$, $Y$ follows $\mathrm{Bin}(n_2,p_2)$, $X$ and $Y$ are independent. What does $X+Y$ follow?</p>
<p>I know the answer, that if $p_1=p_2=p$ then $X+Y$ follow $\mathrm{Bin}(n_1+n_2,p)$ but I do not quite get it. I tried to match $X+Y$ to the criterion of Bin dist... | 72,955 |
<p>In my animal experiments, I do survival studies, which generate Kaplan-Meier survival curves for each group, which I then compare with an appropriate log rank test.</p>
<p>My question is: If I have run a survival experiment with identical variables, say, five times, and the final outcome (in very layman's terms) ha... | 35,116 |
<p>I am almost certain there is/are a technical term(s) to describe transformations (e.g $x^2$ or $log(x)$ for positive numbers) which are non-linear transformations of the variable $x$, but retain the rank order of x. But I am drawing a blank and my google searches have be ineffective. What technical terms apply to ... | 72,956 |
<p>I was wondering what are the differences between Mode, Class and Type of R objects?
Type of a R object can be obtained by typeof() function, mode by mode(), and class by class(). </p>
<p>Also any other similar functions and concepts that I missed?</p>
<p>Thanks and regards!</p> | 72,957 |
<p>I have read a book saying that statistical properties of the mode and the median are difficult to determine compared to the mean. I am not entirely sure why is so.</p>
<p>Is it correct that because the mean can be put into mathematical functions more easily compared to the mode and median? What does it mean by stat... | 72,958 |
<p>I understand how to use the box cox transformation in R and how to get the graph and lambda. </p>
<p>These are the things that are confusing me. For simplicity assume this example:</p>
<pre><code> Weight = Gender + Height + Age + Income
</code></pre>
<p>gender = categorical variable 1 = male, 0 = female</p>
<p>c... | 72,959 |
<p>I would like to address the endogeneity problem in my model. Let me go step by step.<br>
I have panel data for 19 countries, 1995-2010. </p>
<p>My regression model: <code>reg gge et (+control variables)</code> </p>
<p>My independent variable is: energy tax (code: et). </p>
<p>My dependent variable is: CO2 (eq... | 72,960 |
<p>I have recently been reading and trying to understand the Bayesian paradigm and looking at various methods that people have been using to estimate the posterior distribution. Now, it seems that most of the intractability comes from the fact that the likelihood terms have a complex form or there are complex integrati... | 72,961 |
<p>I am considering the linear regression model </p>
<p>\begin{equation}
Y_{i} = A t_{i} + B + \varepsilon_{i}
\tag{$1$}
\end{equation}</p>
<p>where $A$ and $B$ are unknown real parameters and $(\varepsilon_{i})_{1 \leq i \leq n}$ are observed values of independent and identically distributed gaussian random variabl... | 72,962 |
<p>I have a monthly commodity demand and try to forecast this series for the next 5 years. </p>
<p>Here is a plot:</p>
<p><img src="http://i.imgur.com/ccoci40.jpg" alt="Plot"></p>
<p>Of course, the natural approach to forecast this seasonality would be some kind exponential smoothing (e.g. Holt Winters). But my clie... | 72,963 |
<p>I have a returns (finance) dataset with 3 factors, each with 3 levels: industry (banking, retail, others), year (2010, 2011, 2012), and size (small, medium, large). Each factor has been coded as a group of dummies (e.g. IND_BANK, IND_RETAIL, IND_OTHERS). My sample is unbalanced, i.e. some cells do not have data at a... | 72,964 |
<p>I'm working with an array of size 265 x 5000.
Each column is a time series and the rows are points in a series of volumes
( voxels in fMRI ).</p>
<p>I preprocessed this data in several ways, most of which have some sort of filtering mechanism.</p>
<p>My task is to compute the correlation coefficient between all vo... | 35,121 |
<p>This is a fairly general question:</p>
<p>I have typically found that using multiple different models outperforms one model when trying to predict a time series out of sample. Are there any good papers that demonstrate that the combination of models will outperform a single model? Are there any best-practices aro... | 72,965 |
<p>Instrumental variables are becoming increasingly common in applied economics and statistics. For the uninitiated, can we have some non-technical answers to the following questions:</p>
<ol>
<li>What is an instrumental variable?</li>
<li>When would one want to employ an instrumental variable?</li>
<li>How does one f... | 37,823 |
<p>Difference in differences has long been popular as a non-experimental tool, especially in economics. Can somebody please provide a clear and non-technical answer to the following questions about difference-in-differences.</p>
<p>What is a difference-in-difference estimator?
Why is a difference-in-difference estimat... | 72,966 |
<p>We're trying to improve search results, and we're trying to determine if certain changes (adding a word to a synonym list, removing it from the query, etc) have a statistically significant improvement on the results for future searches.</p>
<p>We currently have data for past queries and their matching "correct" res... | 23,522 |
<p>Let $\Delta_{K}$ be the probability simplex of dimension $K-1$, i.e. $x \in \Delta_{K}$ is such that $x_i \ge 0$ and $\sum_i x_i = 1$.</p>
<p>What distributions which are frequently (or well-known, or defined in the past) over $\Delta_{K}$ exist?</p>
<p>Clearly, there is the Dirichlet distribution and the logistic... | 43,393 |
<p>I have a series and I need to check if the values are asymmetric or not (less or more) with respect to the mean.</p>
<p>What test should I use?</p> | 35,126 |
<p>Given a time series, one can estimate the autocorrelation-function and plot it, for example as seen below:</p>
<p><img src="http://i.stack.imgur.com/gp9Vp.png" alt="The time series"></p>
<p><img src="http://i.stack.imgur.com/5sxja.png" alt="ACF"></p>
<p>What is it then possible to read about the time series, from... | 35,127 |
<p>I am an ecology student and have to deal with 10 or 20 field variables, including species frequencies. I need to screen out what variables are most important in the occurrence of a bird species. What book would tell me the methods to do this?</p> | 35,128 |
<p>I'm trying to simulate a data protocol running over a 5 Mbps RF link. The datasheet for the RF chip gives a logarithmic BER vs SNR plot (BER := bit error rate; SNR := signal to noise ratio), but to simplify I am choosing to fix the BER to the same value that many of the RF characteristics are measured: BER = 10^-4.... | 72,967 |
<p>I run into a problem where I would like to build a GEE in R with cubic regression splines (or any other spline type) for a longitudinal data set and an urgent need for grouping and multiple autocorrelation structures. However, I did not find any package capable allowing for that. </p>
<p>If anyone could give a sugg... | 72,968 |
<p>My dependent variable is, by origin, absolute residual* left after some regression; it is <em>distributed half-normally</em>. Now I plan to use Generalized linear model in SPSS (GENLIN) to regress it on some predictors (totally different from those which produced the residuals). What distribution type should I use f... | 46,418 |
<p>I have a machine learning project that uses a bunch of features to predict a class that has categorical values. The possible values are:</p>
<p>1, 2, 3, 4, and 5.</p>
<p>I'm interested whether the class has the value 1 or not. Therefore I added a new binary variable that is 1 when the class is 1 and 0 otherwise. S... | 72,969 |
<p>I performed a PCA on some data related to habitat (different types of vegetation cover, soil water etc.), but there were some variables that I did not include in the PCA because they were not strongly correlated with any of the other variables. I selected the first three principal components from the PCA whose eigen... | 43,450 |
<p>I have two raters who agree on 93% on the cases (two options: yes or no). However, when calculating cohens kappa through crosstabs in spss I get really strange outcomes like -0.42 with a sig. of 0.677.</p>
<p>How can such a high agreement in percentage result in such a strange kappa?</p>
<p>I don´t get it. </p> | 72,970 |
<p>I am conducting a food science test to replace eggs with other alternatives in baking applications. </p>
<ul>
<li>Independent variable: three different formulas (substitution percentages)</li>
<li>Dependent variables: texture profile, moisture, and sensory evaluation</li>
</ul>
<p>In terms of procedure, I would ... | 72,971 |
<p>Can anyone help me understand the <code>forward stagewise</code> part in the LARS algorithm? I was reading the R code and could not figure out what is <code>updateR</code> and <code>downdateR</code> doing.</p> | 40,813 |
<p>For instance, we observed $n$ tossing of a biased coin with probability of heads being $\theta$. How can I calculate this parameter via maximum likelihood? How can I derive the log-likelihood formula and the correct maximum likelihoo estimate of $\theta$?</p> | 72,972 |
<p>What is the relationship between $Y$ and $X$ in the following plot?
In my view there is negative linear relationship, But because we have a lot of outliers, the relationship is very weak. Am I right?
I want to learn how can we explain scatterplots.</p>
<p><img src="http://i.stack.imgur.com/hVoLg.jpg" alt="enter im... | 72,973 |
<p>Suppose I have a 2D point dataset and I want to detect the directions of all the local maxima's of variance in the data, for example:</p>
<p><img src="http://i.stack.imgur.com/OB1Mz.png" alt="enter image description here"></p>
<p>PCA does not help in this situation as it is an orthogonal decomposition and therefor... | 72,974 |
<p>I’m hoping for some help understanding the concept of RVs with respect to their use in the theory of drawing inferences on a population from a sample.</p>
<p>To draw inferences on a population using a sample it is said that the observations must be i.i.d. RV's. I'm considering the example of a weighted die. If you ... | 72,975 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.