question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>When a <a href="http://en.wikipedia.org/wiki/Queueing_theory" rel="nofollow">queueing system</a> is modeled as an M/M/1 queue, it is assumed that the arrival time of jobs has Poisson distribution and the service rate has exponential distribution. I am wondering what features a system should have in order to model th... | 35,629 |
<p>Quick question: I have found <a href="http://www.r-tutor.com/elementary-statistics/analysis-variance/randomized-block-design" rel="nofollow">this tutorial</a> which recommends a two-factorial design for the following setup: three menu items (fixed factor) are tested in six restaurants (random factor). The guide reco... | 73,318 |
<p>Given a R.V $X$ and that $\ E(X) = 0 $ and $\ E(X^2) = \sigma^2 $. Is there anyway to compute $\ E(X^3) $ without knowing the density function of $X$? </p> | 73,319 |
<p>I do experiments with a certain parameter x. The result is y. I assume y is linearly related to x.</p>
<p>Suppose I can do 1000 experiments, which method will give me a better estimation of the linear relation?</p>
<ul>
<li>Select 1000 different values of x, get a single y for each x, and do linear regression?</li... | 73,320 |
<p>I'm fitting a generalized linear mixed model in R using the Laplace approximation. I'm looking for a reference for the Laplace approximation used for that, or a reference regarding the comparison between the PQL and Laplace methods for fitting generalized linear mixed models.</p> | 73,321 |
<p>This figure:</p>
<p><img src="http://i.stack.imgur.com/Q5Lrp.jpg" alt="odds ratios"></p>
<p>shows my odds ratios. I believe they have to be linear for logistic regression to work and am wondering how to pre-process these data. Thanks.</p> | 38,209 |
<p>Is there any reason of what I can think of, to transform the data with a square root? I mean what I always observe is that the R^2 increases. But this is probably just because of centering the data! Any thought is appreciated!</p> | 73,322 |
<p>I have hundreds of explanatory variables and under 100 observations (saturated data set). I'd like to create a linear model in which I have two or so composite variables made up of a dozen of the explanatory variables each. How do I find the best variables to use for the composites without going through every com... | 73,323 |
<p>This is pretty hard for me to describe, but I'll try to make my problem understandable. So first you have to know that I've done a very simple linear regression so far. Before I estimated the coefficient, I watched the distribution of my $y$. It is heavy left skewed. After I estimated the model, I was quite sure to ... | 73,324 |
<p>Question was originally posted <a href="http://stackoverflow.com/questions/6172746/calculate-variance-of-3-or-more-attributes-with-known-frequecies">on Stack Overflow</a>. </p>
<p>I want to calculate variance of data at a given time where I know the frequency of the conditional and decision attributes.
At time $t$... | 73,325 |
<p>I'm trying to implement the extended binomial density function with support on c( 0 : (floor(N) + 1)), but I'm running into (I think) precision issues, as running:</p>
<pre><code>########################
#---DENSITY FUNCTION---#
########################
debinom <- function(k, n, p, sum) {
if (k <= n) {
... | 73,326 |
<p>I want to programatically calculate at which particular hours of a day the probability of a webpage hits(accessed) are high.</p>
<p>Which statistic formula should I use to calculate the peak hours of the web page, if I have already the below data about a page .</p>
<p>e.g. for page xyz, at left I have hours and at... | 73,327 |
<p>I have data on a repeat length polymorphism. For each subject, I have two values, giving the (discrete) number of repeats on each allele. I want to test whether the length of the repeat on one allele and that on the other are independent of each other.</p>
<p>My problem is that there is no natural order in the repe... | 73,328 |
<p>I'm currently working on a self study worksheet. I understand most parts of the solution for part III, but I can't seem to make out how this comes about:</p>
<p><img src="http://i.stack.imgur.com/emSUF.jpg" alt="enter image description here"></p>
<p><strong>QUESTION:</strong></p>
<p><img src="http://i.stack.imgur... | 73,329 |
<p>I have run the Fisher Exact test for several larger than 2x2 matrices. I got a Value number and a P value instead of just a P value. Does this mean the test ran out of memory and is invalid? or...Why did I get a Value?</p> | 73,330 |
<p>I am reading the book "<a href="http://rads.stackoverflow.com/amzn/click/0470539399">how to measure everything</a>", there is a chapter when the author encourages the usage of Monte Carlo simulation in simulating the future events in order to get a better understanding of the risk/ uncertainty involved. The theory s... | 73,331 |
<p>Here is a simple test I've run on MATLAB to check the validity of a single pass (online) algorithm for computing $3$rd moment and $4$th moment.</p>
<pre><code>randn('state',0);
num2 = 0;
num1 = 0;
delta = 0;
M1 = 0;
M2 = 0;
M3 = 0;
M4 = 0;
Xvec = zeros(1, 100000);
for j = 1:length(Xvec)
X = 3*randn(1);
... | 35,643 |
<p>Let's consider the example of whether a person's weight is correlated with their height (simple linear regression). What is the difference between running this correlation on the following two data sets?</p>
<p><strong>Measurements independent of time</strong>
Randomly sample 100 people and record their weight and ... | 35,644 |
<p>I need to plot an interaction between two continuous factors for interpretation. I am using the wireframe function in the lattice package and plotting the predicted values from the model with the best fit. The model looks somewhat like this:</p>
<pre><code>out<-lmer(response~apples+pears+strawberry+mangoes+(mang... | 73,332 |
<p>In the research that I am carrying out I have a moderation in which predictor, moderator and outcome variable are on the different levels: predictor and moderator on within level (the data were collected longitudinally over 6 months, every participant has 10 results) and outcome variable on between level (the data w... | 73,333 |
<p>Suppose that $X$ is a random variable with any distribution that takes only positive values. Can the following inequality hold for constants $c_2 >c_1 >0$?</p>
<p>$$\text{Var}(Z^{c_2})/\text{E}[Z^{c_2}]^2 > \text{Var}(Z^{c_1})/\text{E}[Z^{c_1}]^2$$</p>
<p>In other words:</p>
<p>$$\text{E}[Z^{2c_2}]/\te... | 73,334 |
<p>When splitting attributes while constructing a random tree, I use information gain in order to determine the best value to split the tree on. I add nodes to the tree until a stopping criterion is met. What is the minimum value of information gain, to be used as a stopping criterion?</p> | 35,652 |
<p>I’m trying to make a Liquid State Machine, I have a spiking neural network as the liquid, and a feedforward neural network that should learn to map the reservoir’s states to the output.</p>
<p>I’ve read many articles, but I didn’t find much about how I give the reservoir’s states to the feedforward network’s inputs... | 35,653 |
<p>Like the title says, I've got two time series, one is stationary to begin with and thus has no unit root, the other time serie is stationary after one-time differencing. </p>
<p>I want to create a model out of this and I know that when unit roots are present, I should test for cointegration. But I've read in <a hre... | 73,335 |
<p>For a university project I wrote a SVM classifier and during the benchmark phase I'm getting some results I'd like to better understand from the theoretical side.</p>
<p>My original dataset contains a multi-labeled examples but I'm buiding a binary classifier so I pick a feature <code>A</code> and I replace all the... | 35,654 |
<p>Following on my question <a href="http://stats.stackexchange.com/questions/19227/possible-extensions-to-the-default-diagnostic-plots-for-lm-in-r-and-in-general">for OLS</a>, I wonder: what diagnostic plots exists for quantile regression? (and are there R implementation of them?)</p>
<p>A quick google search already... | 35,656 |
<p>I've some numerical sequence of data monitored over time $v(i)$, which belongs to one of two classes, 0 or 1. I monitor the variable several times, obtaining a sequence associated to 0 or 1.
I use part of the cases in which $v(i)$ belongs to class 0 to have a profile/baseline (training data/cases).
I then use the ca... | 73,336 |
<p>Is it a good or a bad practice to use R packages from CRAN for research? I'm talking about the common packages like: simple models for regression, estimation, econometrics
Most of them use function that can be written easily on your own.</p>
<p>My yes arguments:</p>
<ul>
<li>Time to focus on the main part of the r... | 49,919 |
<p>I have physiological data (electodermal activity) from several subjects recorded continuously during a task with multiple components. I'm interested in comparing whether the response within each component is different (for example: is the response in part D greater/different than in part A). Visually, there is a tre... | 73,337 |
<p>When analysing many real datasets, I have noticed that the most of correlations is positive. For example, here is a visualization of Pearson's correlation matrix for my current data. Is there any reason for this?</p>
<p><img src="http://i.stack.imgur.com/Yec8K.jpg" alt="enter image description here"></p>
<p><stron... | 1,006 |
<p>In the book of Witten and Frank on <em>Data Mining algorithms</em>, I read:</p>
<p><em>"If boosting succeeds in reducing the error on fresh test data, it often does so
in a spectacular way. One very surprising finding is that performing more
boosting iterations can reduce the error on new data long after the error ... | 73,338 |
<p>Suppose $X$ and $Y$ are both normally distributed, with $X \sim \mathcal{N}(0,1)$ and $Y \sim \mathcal{N}(c,1),$ where $c > 0$. Consider $n$ independent draws of both $X$ and $Y$. As $n \rightarrow \infty,$ what is the probability that the sample maximum of the draws of $Y$ is greater than the maximum for $X$?</p... | 35,662 |
<p>I'm looking for someone who is familiar with the ITSM software. I have some data that needs to be fit with an ARIMA/SARIMA model and then forecast using Holt-Winters/Seasonal method. I then need to compare them using RMSE and MAPE.</p>
<p>I'm completely unfamiliar with ITSM and just need some help on the commands ... | 73,339 |
<p>I am running the below mixing model using the <code>rjags</code> package in R, but I keep getting the error message <code>RUNTIME ERROR:Cannot insert node into p[1,1]. Dimension mismatch</code>. I have clearly specified the Dirichlet prior incorrectly but I am unsure what needs changing.</p>
<pre><code>model
{
# Li... | 35,664 |
<p>What is the best technique to calculate a confidence interval of a binomial experiment, if your estimate is that p=0 (or similarly p=1) and sample size is relatively small, for example n=25?</p> | 73,340 |
<p>There is a question about testing whether the interquartile ranges(IQR) from the two non-normal distributions are significantly different.
Now I am looking for a test of significance testing interquartile ranges.
I found some approaches for comparison of IQR, ie.
Westenberg-Mood test
permutation test
boostrap + z te... | 35,666 |
<p>I have recently discovered <a href="http://www.iro.umontreal.ca/~kegl/research/pcurves/" rel="nofollow">Principal Curves</a> while trying to solve the problem I will describe below.</p>
<p>The principle of Principal Curves is to fit a cloud point to find the "path" running along that points.</p>
<p>My goal is to u... | 73,341 |
<p>I was reading some notes and it says that PCA can "sphere the data". What they define to me as "sphering the data" is dividing each dimension by the square root of the corresponding eigenvalue. </p>
<p>I am assuming that by "dimension" they mean each basis vector into which we are projecting (i.e. the eigenvectors ... | 73,342 |
<p>I am reviewing the R package OpenMx for a genetic epidemiology analysis in order to learn how to specify and fit SEM models. I am new to this so bear with me. I am following the example on page 59 of the <a href="http://openmx.psyc.virginia.edu/docs/OpenMx/1.0.0-1448/OpenMxUserGuide.pdf">OpenMx User Guide</a>.</p>
... | 73,343 |
<p>I am trying to apply R depmixS4 package in order to cluster time series with model based clustering. The model consists of K components, each being a first order Markov models. The Expectation-Maximization algorithm is then used to estimate model parameters. </p>
<p>My time series are multivariate and of arbitrary ... | 73,344 |
<p>I want to include sample weights to my quantile regression model, but I'm not sure how to do this. </p>
<p>I've already define my weight, which are replicated weights already given in survey dataset (computed in survey package): </p>
<pre><code>w<-svrepdesign(variables=data[,1:10],repweights=data[,11:30],type=... | 35,670 |
<p>I apologize if this is too simple a question for this forum but...</p>
<p>If I'm trying to build a neural network or other machine learning based prediction of who will win a football game and by how many points given such and such inputs do I use the actual score of past games as the correct answer for my neural n... | 73,345 |
<p>Currently iam working on my master thesis which is about risk adjusted returns in the Asia Pacific REIT market. The goal of the paper is to determine/find variables that conceive explanatory power over the IV. </p>
<p>To determine this I also performed a FE regression based on countries. The result are more or less... | 73,346 |
<p>I am working on sample size of 70 . My observed and expected values are different
(Observed 586,
648,
526,
662,
658,
502,
..... so on for 70 samples and expected 570
634,
513,
647,
644,
490,
.....so on for 70 samples). I used Chi-sq test to check the null that there is no difference in observed and expected value. A... | 73,347 |
<p>I have two sets of data that hypothesis tests have shown to be normal and from the same distribution. I'm using MATLAB and for the way they give p-values, higher p-values suggest a better goodness-of-fit, as I understand it. I want to combine the two data sets to get the parameters for the combined data set. Howe... | 26,916 |
<p>I was wondering if somebody could help with trying to visualise some data. </p>
<p>I have 11 groups of organisms and have related them to levels of a specific bacteria in water samples. I have a strong positive relationship between the proportion of one of the groups and some non-significant relationships in others... | 73,348 |
<p><img src="http://i.stack.imgur.com/4dw9Z.jpg" alt="The Conjugate Beta Prior"></p>
<p>Hello.
I'm having a problem with trying to figure out this proof that shows the beta
distribution is conjugate to the binomial distribution (picture attached).
I understand it until the third row, but I got confused with this step... | 73,349 |
<p>I'm trying to analyse the performance of my server by collecting performance data using standard tools such as Windows Performance Monitor, and then putting this data on Excel for analysis.</p>
<p>When I set up the data collector (as it's called), I can chose different intervals for collection, such as every 1 seco... | 73,350 |
<p>Is it possible to add standard error or confidence interval to a plot of a predicted vs observed values derived from a multiple regression model? I believe that I have seen such plots as an output in Statistica, but am unsure how to create them in R.</p>
<p>I believe I have a solution (below), but am unsure that I ... | 35,680 |
<p>I have made a factor analysis of one construct (i.e. difference between two countries) and got two distinct factors (1=cultural differences, 2=economical environment). I extracted the scores as I want to check if the score of cultural differences is bigger than economical. How do I do that? I have tried making a sim... | 35,682 |
<p>I'm reading this chapter
<a href="https://www.otexts.org/fpp/4/1" rel="nofollow">forecasting principles and practise</a> from a forecasting book.</p>
<p>The author has explained a linear regression model. Now this linear regression model will definitely have some errors in fit. For these errors, the author has lis... | 49,560 |
<p>I'm attempting a project where I need to statistically rank available cars based on several variables such as cost, mpg, seating, milage, etc.. I wish to rank these cars in order decide which car would be the best choice (highest "worth") to buy (or best several cars if I was informing multiple people of the best ca... | 73,351 |
<p>I have two variables <em>Distance</em> and <em>Slope</em>. These go into a model resulting in a <em>cost</em> variable. I like to figure out the influence of the variables Distance and Slope on the Cost variable. I have several hundred test numbers for the variables. What programs or steps could I use to see the imp... | 73,352 |
<p>I would like to compare the means of the same group on two continuous scales. I want to see if the scores are significantly different on the scales. Which statistical test do I use for this? </p> | 35,685 |
<p>I have a problem that seems tractable, which I will attempt to describe with classic balls and buckets probability nomenclature.</p>
<p>Imagine someone brings you a bag of colored balls. This sample was selected at random from one of many large buckets of balls. Each bucket contains 1,000,000 balls, and each ball... | 73,353 |
<p>Can someone explain the intuition behind the split plot. From what I understand, its is essentially restricted randomization. But I still quite understand it. Is there a resource or example anyone can give me to make it clearer?</p> | 43,656 |
<p>I use <code>cpgram</code> function in R to produce a cumulative periodogram of a monthly time series. Its horizental axis is a number between 0 and 6 labeled as frequency: what does these numbers mean, since the frequency in cumulative periodogram should be between 0 and 0.5 like the ones shown below (upper ones)?</... | 73,354 |
<p>Can someone provide a work flow about this? For instance, suppose I am doing binary classification,</p>
<p>For each iteration of the algorithm:</p>
<p>Randomly sample k*N rows, where k is the bag.fraction, and N is nrow(dataset).</p>
<p>Build a classifier using this training sample, suppose we use classification ... | 35,687 |
<p>I know about the following tests:</p>
<ul>
<li>Mantel-Haenszel for categorial stratified data</li>
<li>Kruskal-Wallis for nonparametric ANOVA for more than two treatments</li>
<li>Friedman for a repeated measures version of Kruskal-Wallis</li>
<li>van Elteren for nonparametric comparisons of stratified data between... | 73,355 |
<p>I wish to measure the "diversity" of a group of objects. Right now I'm using Euclidean distance to compute the similarity matrix between all the objects in the group.</p>
<p>I'm searching for a measure of this diversity to decide if replacing an element of this matrix with a new one will make the group more or less... | 73,356 |
<p>Following the <a href="http://en.wikipedia.org/wiki/Tobit_model" rel="nofollow">wiki page</a> and the form of the likelihood function for a generalized Tobit model presented <a href="http://support.sas.com/documentation/cdl/en/etsug/63348/HTML/default/viewer.htm#etsug_qlim_sect022.htm" rel="nofollow">here</a>, I am ... | 73,357 |
<p>I am going through this paper <a href="http://prac.im.pwr.wroc.pl/~mbogdan/TE/materials/Efromovich_Wiley_interdisciplinary_reviews_2010_orthogonal_series.pdf" rel="nofollow">Orthogonal series density estimation</a>. I have a doubt in following</p>
<p>Assume that the random variable X is supported on [0, 1], that is... | 73,358 |
<p>According to some articles (e.g. <a href="http://brenocon.com/blog/2012/03/cosine-similarity-pearson-correlation-and-ols-coefficients/" rel="nofollow">here</a>) correlation is just a centered version of cosine similarity. I use the following code to calculate the cosine similarity matrix of the column vectors of a m... | 73,359 |
<p>There are a set of ("artifical") not Minkovski (triangle inequality is not guaranteed) metrics defined on set of objects.</p>
<p>There are one etalon ("natural") metric, which estimation is known only for some objects (a finite learning subset).</p>
<p>How can I get some combination of "artifical" metrics (new met... | 73,360 |
<p>I'm trying to make a model to forecast the electricity price, a time series model with R and i have some questions</p>
<p>Our data are daily price of the past 3 years from north pool countries, and we are trying to do a model to forecast the daily prices too. </p>
<p>We don't know how to descompose the seasonality... | 73,361 |
<p>I have been wanting to get away from using power calculation tools (JMP, Lenth) in favor of Monte Carlo techniques to determine the a-priori power to observe factor level effects in a DOE. I am really new to this and have a few questions. Lets start with what I have:</p>
<ol>
<li>A binomial response which I plan ... | 73,362 |
<p>Good evening everyone, </p>
<p>I am working on the following self-test question for regressions, but my answer 26.901 seemed really different from the model answer 27.2155.</p>
<p><strong><em>Question</em></strong></p>
<blockquote>
<p>A hotel derives its gross income from its hotel and restaurant operations.
... | 26,981 |
<p>I am looking for the word/phrase that is used to say that a (potential) erroneous conclusion has been drawn from data without having a correlation to other supporting data points.</p>
<p>For example, if someone has the dataset of the number of red cars sold in the US per month as <code>Jan: 10, Feb: 10, Mar: 9, Apr... | 73,363 |
<p>A gaussian random vector $X$ can be represented using a graph where two nodes $a$ and $b$ are connected $\Leftrightarrow X_a$ is dependent on $X_b$ given all the remaining random variables. I have two questions - </p>
<p>1) It is stated that the neighborhood of $a$ is the smallest subset such that given this subset... | 1,007 |
<p>P-value is defined the probability of obtaining a test-statistic at least as extreme as what is observed, assuming null-hypothesis is true. In other words,</p>
<p>$$P( X \ge t | H_0 )$$
But what if the test-statistic is bimodal in distribution? does p-value mean anything in this context? For example, I am going to ... | 35,695 |
<p>This is not homework. Just practicing for an upcoming exam. Question is taken from a web pdf : <a href="http://www.dartmouth.edu/~chance/teaching_aids/books_articles/probability_book/Chapter11.pdf" rel="nofollow">http://www.dartmouth.edu/~chance/teaching_aids/books_articles/probability_book/Chapter11.pdf</a></p>
<p... | 73,364 |
<p>The beta distribution is conjugate prior for the binomial distribution.</p>
<p>Is the beta-binomial distribution a conjugate prior for some sampling distribution?</p> | 35,697 |
<p>Panel estimators such the one implemented in the R package <code>plm</code> allow to estimate <code>"individual"</code>, <code>"time"</code> or <code>"twoways"</code> effects.</p>
<p>See <a href="http://cran.r-project.org/web/packages/plm/vignettes/plm.pdf" rel="nofollow">http://cran.r-project.org/web/packages/plm/... | 73,365 |
<p>There have been threads here before which posted links of the media attributing causality to correlational studies, and links to those studies have been posted. It seems as if we are always focusing on showing students how to identify correlations and not to confuse it with causality.</p>
<p>We are missing somethin... | 73,366 |
<p>I'd like to measure the duration of a function call. The function call has one parameter, <code>n</code>. If I were to graph an average of the function call's duration, with <code>n</code> on the x axis, I would also provide the standard error for each <code>n</code>.</p>
<p>The function call duration is, however, ... | 73,367 |
<ol>
<li>Using either percent error or percent difference, I want to compare one of my measured values from a set to the mean of the set. By reading the Wikipedia article on <a href="http://en.wikipedia.org/wiki/Percent_difference" rel="nofollow">percent difference</a>, it's still not quite clear which I should choose.... | 35,699 |
<p>The data for my variable is in the form of Z-scores only. I'd like to log transform the scores, but I don't know the mean or standard deviation in order to covert to raw scores. Can I assign an arbitrary mean and standard deviation, use that to convert to raw scores, then log transform the raw scores? Or is there so... | 73,368 |
<p>I wonder why gene expression data are very frequently modeled by multivariate normal distributions. What is the reason for those strong assumptions that the genes follow multivariate gaussian? Are there any reasons specific for genetics other than the reasons for general gaussian assumptions (mathematical convenienc... | 73,369 |
<p>I understand how differential calculus is useful for basic Maximum Likelihood estimation techniques. However, my question is: what broad types of statistics require an understanding of integral calculus?</p> | 73,370 |
<p>I was recently told that it was not possible to incorporate time-varying covariates in longitudinal mixed models without introducing a time lag for these covariates. Can you confirm / deny this? Do you have any references on this situation ?</p>
<p>I propose a simple situation to clarify. Suppose that I have repeat... | 27,014 |
<p>I am working with the two step cluster process in SPSS Modeler (Clementine) and trying to get a sense for the distance function used. It is a log-likelihood function (as stated in docs) but I am unsure for even the continuous variables (the function handles continuous and nominal variable) how this is a log likeliho... | 73,371 |
<p>Usually, we can test difference of two groups of data by adding the dummy variable. But my question is, if these two groups of data in the same line, but they concentrate at the different part of this line. Is there any way we can test difference?
For example,in group one, our data set is $(x_{1i},y_{1i})$, in group... | 35,706 |
<p>Can I use a chi-squared test to compare two empirical distributions?</p>
<p>Signs point to "yes." <a href="http://stat.ethz.ch/R-manual/R-patched/library/stats/html/chisq.test.html" rel="nofollow">R's chisq.test</a> allows two vectors x and y. It says:</p>
<blockquote>
<p>cases with missing values are removed,... | 35,707 |
<p>I have a bunch of points that belong to one of population P1, P2, ... Pn AND to class A or B.</p>
<p>Within each population I'll be doing classification between A and B, and I want to select features that discriminates the best between A and B. Now, my features are also correlated with population membership, but I ... | 73,372 |
<p>Is there a simple example for a pair of hypotheses for which a uniformly most powerful (UMP) test does not exist? How does one go about proving this? Is it true that for tests with double-sided hypotheses, a UMP test does not exist? Is it true that for multivariate parameters, a UMP tests does not exist?</p> | 73,373 |
<p>Suppose that $x$ takes the following values: 0 feet from start, 10 feet from start, and 15 feet from start. Let the outcome variable be $y$. How would you interpret the regression coefficient of $x$ ($\beta_1$) in a linear regression? Would it be: a unit increase in $x$ is associated with an expected increase of $\... | 73,374 |
<p>Folks, pardon my noobness but I have not touch maths for some time and need a refresher into statistics:</p>
<p>I read that in Bayes rule, the denominator of <code>P(params|data) = L(params)P(params)/P(data)</code> is called a normalizing constant. Can anyone explain why does integrating f(data|params)f(params) as ... | 73,375 |
<p>What is v-fold cross validation in relation to k-fold cross validation?</p>
<p>Also is there a more common way in which v-fold cross validation is referenced?</p>
<p>I'm struggling to find resources on this method.</p> | 73,376 |
<p>The definition for the $k$-th lag auto correlation is $Cov(y_t,y_{t-k})/Var(y_t)$.<br>
My question is why should not it be $Cov(y_t,y_{t-k})/[Var(y_t)\cdot Var(y_{t-k})]^{0.5}$.<br>
In another words, what is it different from the correlation coefficient between $y_t$ and $y_{t-k}$?</p> | 73,377 |
<p>I have a set of data with an ordinal response ranging from <code>1-5</code> (worst to best) and a categorical predictor with five unordered levels. The experiment is a language experiment whereby subjects are asked to rate different sentence types. In the literature it seems that people fit <code>lmer()</code> most ... | 73,378 |
<p>Following the design and data described in <a href="http://stats.stackexchange.com/questions/11887/is-this-design-a-one-way-repeated-measures-anova-or-not">this question</a>, I did a simple one-way within-subjects repeated-measures (RM) ANOVA and found some significant p-values. I then applied non-orthogonal post-ho... | 73,379 |
<p>I want to estimate the parameters of a function of general form $y = a \cdot x^b$. I applied a log-log transformation to obtain a linear function of the form $\log y = \log a + b \times \log x$. I have fitted the linear model in MATLAB.</p>
<p>MATLAB computes the goodness of a fit in terms of sum of squares error (... | 73,380 |
<p>I have a set of points which is a count of links that users have clicked on : </p>
<pre><code> link1,link2,link3,link4
user1, 0 ,2 ,3 ,2
user2, 1 ,4 ,0 ,5
</code></pre>
<p>I am not sure which distance function I should use to calculate the distance between users. I think Eucl... | 73,381 |
<p>Suppose that I have a linear model with autocorrelated errors. Is there any results telling me that if I assume iid errors I overestimate or underestimate my standard errors ? </p> | 361 |
<p>I have a question on coding a Likert scale in SPSS.</p>
<p>Assuming we have a 7-point Likert scale, a "well-being" score may rank from 1 through 7.</p>
<p>While doing some reading on multi-variate analysis, I've come across a reference that suggests a "deviation score". That is, it's ranging from [-3, -2, -1, 0,... | 35,715 |
<p>I have a dataset containing values representing monthly sales in hypothetical e-commerce website. First columns contains order of particular month (eplanatory variable) and the second column (dependent variable) is value of sales in this month.</p>
<pre><code>month_order value
1 2591
2 2262
3 2531... | 18,512 |
<p>This is somewhat of a beginner's question, but how does one interpret an exp(B) result of 6.012 in a multinomial logistic regression model?</p>
<p>1) is it 6.012-1.0 = 5.012 = 5012% increase in risk?</p>
<p>or</p>
<p>2) 6.012/(1+6.012) = 0.857 = 85.7% increase in risk?</p>
<p>In case both alternatives are incorr... | 38,182 |
<p>The z-test to compare two proportions is $\newcommand{\p}{\hat{p}}\newcommand{\v}{\mathrm{Var}} z=\frac{\p_1-\p_2}{\sqrt{\v(\p_1-\p_2)}}$. Usually it is defined that </p>
<p>$$\v(\p_1-\p_2)=\p(1-\hat{p})(1/n_1+1/n_2),$$ </p>
<p>where </p>
<p>$$\p=\frac{n_1 \p_1+n_2 \p_2}{n_1+n_2}.$$</p>
<p>Is there any written r... | 73,382 |
<p>My data-set consists of points in globe. Suppose a User visits locations $l_1,l_2,\dots l_n$ (each location in $(lat, long)$ in the city with probability $p_1,p_2,\dots,p_n$ and I want to calculate the expected location visited by the user. How should I go about calculating that? If I use geodesic distance between p... | 73,383 |
<p>I have done an experiment of how different animal species affect nutrient fluxes in sediments. I had a number of experimental units (sediment boxes) to which different animal species were added. I then measured nutrient fluxes in these units. Each unit was measured five times. I have used the ezANOVA package for R t... | 27,063 |
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