question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>I am working on a very large dataset of patients who belong to one of five groups. I want to test if groups are not so much different than each other in terms of age, race, sex, smoking level, weight, and some other factors. Some factors are numerical and some are categorical. I know I can use ANOVA to compare mean ... | 69,840 |
<p>I applied libsvm to build a text classifier. The output looks like as follows:</p>
<pre><code>w[a_b] = 0.006
w[a_c] = 0.032
w[a_ctif] = 0.000
w[a_cs] = 1.009
w[aa_d] = 0.000
w[a_e] = 0.001
</code></pre>
<p>The terms, e.g., a_b, and a_c, etc are the features generated for characterizing these documents. My questio... | 69,841 |
<p>The following two statements produce different results.</p>
<pre><code>/* DV: "price" e.g., from 0 to 100 */
/* IV: "treatmentA", "treatmentB" both binary variables */
/* statement 1 */
anova price treatmentA##treatmentB
/* statement 2 */
generate A_x_B = treatmentA * treatmentB
anova price treatmentA treatme... | 69,842 |
<p>I could not find a package in R about Treatment Effect Analysis. </p>
<p>So is there a R package about Treatment Effect Analysis?</p>
<p>This means, estimating the average treatment effect, average treatment effect on the treated using different methods, including algorithms such as k-nearest-neighbour matching, c... | 69,843 |
<p>this question is about a way of presenting the results of an interaction I thought of, and I'm looking to see if it makes sense. If there is a better way to do what I'm trying to do (or if what I'm trying to do is not advisable), please let me know.</p>
<p>To simplify, let's say I've got a multiple linear regressio... | 69,844 |
<p>Reading <a href="http://psg-mac43.ucsf.edu/ticr/syllabus/courses/26/2003/01/16/Lecture/readings/Pocock.pdf" rel="nofollow">Pocock et. al on subgroup analysis</a>, the authors describe calculating an interaction test given 2 odds ratios (and the count data used to get them). Specifically,</p>
<pre><code>mat <- m... | 69,845 |
<p>I have built a linear model using <code>lm</code> in R</p>
<pre><code>lm(age ~ sibsp + parch + pclass, trainset)
</code></pre>
<p>Here <code>sibsp</code> is the number of siblings/spouses aboard the Titanic, <code>parch</code> is the number of parents/children aboard and <code>pclass</code> is the passenger class ... | 69,846 |
<p>My bioinformatical problem looks like this:<br>
two sets of gene sequences (size of set A > 1000, size of set B > 1000; sequence length varies from 1000 to 100000). </p>
<blockquote>
<p>Set_A_Sequence_1: ACGTACGTACGT...<br>
Set_A_Sequence_2: ACGGAAGT <strong>AAA</strong> T...<br>
....<br>
Set_B_Se... | 69,847 |
<p>What is the different between onee vs all and one vs one SVM classifier??</p>
<p>Is One vs All mean = 1 classifier to classify all types /categories of the new image
and one vs one mean= each type /category of new image classify with different classifier (each category is handled by special classifier)??</p>
<p>Fo... | 22,578 |
<p>I'm doing a quantitative study entitled "Technology Transfer and Competitive Advantages in Oil and Gas Companies". </p>
<p>In my study, the unit of analysis is the organization and there are only 9 oil and gas companies in my country. The respondents will be randomly selected from the managerial level (stratified) ... | 40,820 |
<p>Edit: Perhaps my first asking (see below) was a little too ambitious. The crux of the question is this: in a linear regression setting, is there anything statistically invalid about regressing the residuals of a previous model on new predictors (assuming the observations are IID, plenty of degrees of freedom, etc)? ... | 30,478 |
<p>I am a bit confused with the difference between an SVM and a perceptron. Let me try to summarize my understanding here, and please feel free to correct where I am wrong and fill in what I have missed. </p>
<ol>
<li><p>The Perceptron does not try to optimize the separation "distance". As long as it finds a hyperplan... | 69,848 |
<p>Suppose jars are being filled with Red, Green and Blue balls in an approximately fixed ratio. The total number of balls that fits in a jar is fixed (say N=1000). I know the mean and standard deviation of the ratios; let's say means for (R,G,B) are 0.5,0.4,0.1 and stdevs are 0.05,0.05,0.02. They appear to be approxim... | 30,480 |
<p>I have previously posted a question for the same <a href="http://stats.stackexchange.com/questions/30664/suggestion-about-morphometric-analysis-in-r-using-lm-or-lme">dataset</a> but now I had somme issues with the models and I wanted to re-phrase my question.</p>
<p>My dataset contains 50 morphometric characters (w... | 69,849 |
<p>I am trying to figure out the inner workings of the mob function in the party package. I can't figure out how the splitting variable is selected when it is a categorical variable.</p>
<p>In the publications by the authors, they say that it is done by a chisquare test of association between the residual deviances an... | 69,850 |
<p>Description of the problem:
The effect of a certain treatment is tested as follows: For n subjects, the endpoint is measured three times before and after the treatment is administered, respectively. The endpoint is modeled as an ordinal variable with outcomes A,B,C and order $A<B<C$. </p>
<p>There are two que... | 30,482 |
<p>Say the null hypothesis is that two samples emanate from two distributions with either equal medians or equal variances. And p values are the probability that a value or more extreme comes from the original distribution given the null hypothesis holds. Therefore, why do correlations with low p-values mean that they ... | 40,825 |
<p>I have performed an experiment testing 3 different modes of operation on 16 participants. Each mode of operation was tested twice per user. </p>
<pre><code>User Mode Trial1Time Trial2Time
1 1 20 30
1 2 5 7
1 3 40 25
2 1 ... | 69,851 |
<p>Any covariance matrix $A$ must be non-negative definite or semi-positive definite. This means that its deteraminant should always $|A|\ge0$.
In case $|A|=0$, what would happen? or what does this mean for the dependence of the corresponding random variables?</p>
<p>Million thanks for your answers and hints</p> | 49,837 |
<p><img src="http://i.stack.imgur.com/Sgd9z.png" alt="enter image description here"></p>
<p>I am having trouble getting started with this question. Is there a formula for finding point predictions and prediction intervals? Any advice or hints would be great! </p>
<p>Let $\varepsilon$ be defined as white noise.</p>
... | 69,852 |
<p>I've standardized all the variables (even the response variable) and then I've split my data into a training and test part. And for example, I've got the following model based on my TRAINING set:
y = 0.5x_1 - 0.2x_2</p>
<p>Now I shall get values for y like -0.4,0.7,... but I want to say something about the origina... | 30,491 |
<p>How can I represent this problem as a function. Bear with me because it may seem odd.</p>
<p>Say, for example I make cakes. There are 30 variations of cake in one batch. For each batch there are 19 luxury set ingredients and a lot of secondary ones, of which there must be 100% of the luxury ingredients in at least ... | 69,853 |
<p>I am a researcher from India and working in the field of Computational Linguistics for quite some time.
I have lately started working in the field of Machine Learning based algorithms. To do this I tried to master over
statistics, and tried to read the book by Ethern Alpaydin, attended lectures in Coursera by Profe... | 69,854 |
<p>I am beginning to learn statistics and made some searches in Internet about statistics.
Most of the articles I found says that there are two different approaches (or schools, or methods) in statistics Frequentist and Bayesian. But one <a href="http://labstats.net/articles/overview.html" rel="nofollow">article</a> sa... | 30,494 |
<p>I'm doing some imputation models of time until recurrence of tuberculosis (Cox model). This model should include an interaction between the time and the outcome of the previous episode of disease (0- cured, 1-default).</p>
<p>I realized that one should include all information before imputation, in order to built a ... | 69,855 |
<p>As defined <a href="http://www.zoology.ubc.ca/~whitlock/bio300/overheads/overheads16.pdf" rel="nofollow">here</a>, the estimation of the coefficient of correlation is</p>
<p>$$r = \frac{\Sigma (X_i-E[X])(Y_i-E[Y])}{\sqrt { \Sigma (X_i-E[X])^2 \Sigma (Y_i - E[Y])^2}}$$</p>
<p>and the standard error of $r$ is</p>
<... | 30,499 |
<p>I have some data that I can't necessarily assume to be drawn from normal distributions, and I would like to conduct tests of equivalence between groups. For normal data, there are techniques like TOST (two one-sided t-tests). Is there anything analogous to TOST for non-normal data?</p> | 69,856 |
<p>From <a href="http://www.zoology.ubc.ca/~whitlock/bio300/overheads/overheads16.pdf" rel="nofollow">this source</a>, the estimation of the coefficient of correlation is</p>
<p>$$r = \frac{\Sigma (X_i-E[X])(Y_i-E[Y])}{\sqrt { \Sigma (X_i-E[X])^2 \Sigma (Y_i - E[Y])^2}}$$</p>
<p>If the coefficient correlation is null... | 30,501 |
<p>Actually, I have read a pair of books about time series analysis, but I am still not sure about how to treat deterministic components, like trend and seasonality, in the exogenous variables in a time series model. Do I have to detrend and deseasonalize the covariates before I use them as axplanatory variables in a t... | 69,857 |
<p>I have problems in using the <code>cor()</code> and <code>cor.test()</code> functions.</p>
<p>I just have two matrices (only numerical values, and the same number of
row and columns) and I want to have the correlation number and the
corresponding p-value.</p>
<p>When I use <code>cor(matrix1, matrix2)</code> I get... | 69,858 |
<p>I need to predict the outcomes of a time-series variable $Y$ based on two time-series predictors $X1$ and $X2$. For simplicity I will only illustrate $X1$ in the rest of this question.</p>
<p>The correlation between the predictors and $Y$ at lag 0 is relatively high as illustrated by the cross-correlation function.... | 69,859 |
<p>If we build a classifier based on a very small number of instances (say, fewer than 300) and the number of features we are using is very large (say, larger than 100k features). If we decide to introduce a feature selection step before building the classifier, is there a rule of thumb on how many features we should c... | 69,860 |
<p>I am using 10 independent variables in building logistic regression model. I am sure that some of these variable are correlated. Can anybody tell me how to check for multicollinearity among independent variables in this case. Thanks!</p> | 30,513 |
<p>I'm currently working with a data set that consists of a monthly case count for several sites, along with a number of site-specific covariates. We're trying to estimate the effect of one of them on the case-load (either in terms of numbers or a percent). At the moment, I've been using Peng and Dominici's <em>Statist... | 69,861 |
<p>I would like to compare two models using the BIC and AICc. Doing so seems fairly straightforward if both models are fit to only one dataset. However, I have data from 10 participants, and there is no reason to assume that they are all well-described by the same set of parameters.
Is it appropriate to sum the log-lik... | 30,517 |
<p>I have very little knowledge of time-series analysis (despite my stat master - didn't do anything else than an introductory course) but now I'm facing a statistical problem whose answer is this very kind of analysis - so would really need a helpful hand.</p>
<p>In a nutshell, I have account monthly sales. In only <... | 69,862 |
<p>Consider the simple interaction equation where moderator M determines the effect of X on Y.
$$
Y=\beta_1X+\beta_2M+\beta_3XM \quad (1)
$$
then the slope on X is
$$
\frac{dY}{dX}=\beta_1+\beta_3M \quad (2)
$$
Fine.
Now suppose that $M=X/Z$.
You might say that M is just a linear transformation of X, but if X and Z ar... | 69,863 |
<p>I'm an academic in biology and I'm trying to improve my working knowledge of probability and probabilistic methods. I was recommended the <a href="http://www.athenasc.com/probbook.html" rel="nofollow">Introduction to Probability</a> textbook as an excellent introduction to the subject.</p>
<p>I am, however, finding... | 37,906 |
<p>I heard that the power of a t-test used with unequal samples is limited by the size of the smaller sample. Can I take this to mean that the power of a t-test with unequal sample sizes is equal to the power of a t-test used on equal sample sizes where $n$ equals the size of the smaller sample? </p> | 30,519 |
<p>I have a dataset, I want to create clusters on that data based on only one variable (there are no missing values). I want to create 3 clusters based on that one variable.</p>
<p>Which clustering algorithm to use, k-means, EM, DBSCAN etc.?</p>
<p>My main question is, in what circumstances should I use k-means over ... | 47,828 |
<p>use <code>zeroinfl {pscl}</code></p>
<p>I specified offset only for the poisson part. The regression estimate zeroes using regressor <code>zeros</code></p>
<pre><code>zeroinfl(formula = response ~ 1 | zeros, offset = predictor, dist = "poisson")
Pearson residuals:
Min 1Q Median 3Q Max... | 69,864 |
<p>In page 292 of Introduction to Mathematical Statistics by Hogg and Craig it is stated that in order for the variance of the sample variance, i.e. $\text{var}(S^2)$ to exist we need to assume that $E[X^4]<\infty$, that is the fourth (uncentered) moment of our RV is finite. My question is, how do these two connect?... | 30,521 |
<p>I am trying to determine if I can model my system as a M/M/1 queue and if so do the numbers I get from it help me at all.</p>
<p>I can model my system like this:</p>
<p><img src="http://i.stack.imgur.com/dLpOm.jpg" alt="block diagram"></p>
<p><strong>System Description</strong></p>
<p><strong>A.</strong> I want ... | 40,863 |
<p>I'm analyzing a noisy time series where where the inter-event interval is known to follow a two-gamma mixture distribution. If there was a simple model that would generate that kind of thing, it would be pretty simple to implement into BUGS. But otherwise, I can't think of anything that wouldn't be prohibitively kl... | 69,865 |
<p>SAS EM has a node that generates the transformation for a dataset that makes it best fit a normal distribution. I can't imagine the people at SAS are the only ones to figure out how to do this. Is there any documentation out there on methodologies that do the same? Or an open source implementation?</p> | 30,523 |
<p>I study labor and delivery as an epidemiologist. It is well established that a large fetus has a higher risk of causing maternal birth trauma. But a large baby is also likely to be delivered by cesarean section due to difficult labor. Those delivered by cesarean section will not have any risk for maternal birth tr... | 69,866 |
<p>I'm working on a meta-analysis and have generated a quirky question for which I'm at a bit of a loss. The MA is for a large set of factorial experiments. Calculating the Log Response Ratio (LRR) and variance in said ratio for the experimental data is a cinch, and we're comparing the effects of one type of treatmen... | 69,867 |
<p>I use NN for my mini project research, and I found out the newest trick for feed forward NN is using dropout for regularization instead of L1/L2 norm and rectified linear unit as an activation function.</p>
<p>But when I tried it, I always got worse results compared to a standard NN with sigmoid / hyperbolic tangen... | 69,868 |
<p>I'm reading <a href="http://file.scirp.org/Html/8-72278_30995.htm" rel="nofollow">this paper</a> but i don't understand why the result of covariance and why the formula is different. </p>
<p>I am using elliptical Gaussian joint probability density function (pdf) of <a href="http://graphicon.ru/oldgr/en/publicatio... | 69,869 |
<p>I'm coding a <strong>McMC</strong> algorithm for geophysical applications. </p>
<p>Using the Metropolis–Hastings scheme to accept/reject the proposed models is something that I thought I understood completely, but I don't. To be clear:
normally you have a current model $m$, you perturb one parameter (in my case vel... | 69,870 |
<p>I have done rANOVA in SPSS and then in R and got two different p-values from the same model. While SPSS gives 0.032, R gives 0.0162, which when rounded is a half. Other data are exactly the same.</p>
<p><strong>1. Why?</strong></p>
<p>Intuitively, one of them does a one-tailed, the other a two-tailed test. Other v... | 69,871 |
<p>There seems to be a large body of applied research where distribution q is picked to minimize <a href="http://en.wikipedia.org/wiki/Kullback%E2%80%93Leibler_divergence" rel="nofollow">KL(q,p)</a> where p is empirical distribution. Are there theoretical reasons to prefer this estimator? For instance, a theoretical re... | 69,872 |
<p>To avoid over fitting for K-NN could you increase the value of K to reduce anomalous results etc. However, if the value of K is very large with respect to a sample, would this also incur in over fitting?</p>
<p>To avoid over fitting in decision trees should you increase the depth of the tree to allow more rogue val... | 69,873 |
<p>I'm trying a very simple model: fitting a Normal where I assume I know the precision, and I just want to find the mean. The code below seems to fit the Normal correctly. But after fitting, I want to sample from the model, ie generate new data which is similar to my <code>data</code> variable. I know I can use <code>... | 30,529 |
<p>It isn't clear to me how to calculate cointegration with irregular time series (ideally using <a href="http://en.wikipedia.org/wiki/Johansen_test">the Johansen test</a> with VECM). My initial thought would be to regularize the series and interpolate missing values, although that may bias the estimation.</p>
<p>Is ... | 30,530 |
<p>Besides taking differences, what are other techniques for making a non-stationary time series, stationary?</p>
<p>Ordinarily one refers to a series as "<a href="http://en.wikipedia.org/wiki/Order_of_integration">integrated of order p</a>" if it can be made stationary through a lag operator $(1-L)^P X_t$.</p> | 30,532 |
<p>I am trying to explore the relationship between a customer satisfaction rating and a response time (in days). I have been using linear, logistic and quantile regression, to no avail. I believe the issues lies with the distribution of the data. 85% of respondents give a 9 or 10 rating (regardless of response time)... | 26,493 |
<p>I understand that a problem will be inevitable if the variables have different scales of measurement.</p>
<p>My inclination is to think that even if the variables have the same scale of measurement it would be <em>incorrect</em> to simply sum (or to simply average) the raw scores of the variables that are "enough l... | 45,742 |
<p>Say I have two sets, A and B, with a different amount of X,Y points </p>
<p>Is there a way to calculate how similar the data is?</p>
<p>So something like this would be ~65%?, because they partial overlay.</p>
<pre><code>| B8
|
| ... | 69,874 |
<p>While it is often mis-used, I'd like to provide users of <code>ezANOVA()</code> (from the <a href="http://cran.r-project.org/web/packages/ez/index.html" rel="nofollow">ez</a> package for R) with the ability to specify covariates for ANCOVA. Since
<code>ezANOVA()</code> uses a combination of <code>stats::aov()</code... | 69,875 |
<p>Are there any packages to do piecewise linear regression, which can detect the multiple knots automatically? Thanks.
When I use the strucchange package. I could not detect the change points. I have no idea how it detects the change points. From the plots, I could see there are several points I want it could help me ... | 32,369 |
<p>Can anyone show me what the connection between bootstrap methods and maximum likelihood is? </p>
<p>I was told that as the number of bootstraps goes to infinity, the statistics like confidence intervals, mean, variance and stability are same values that maximum likelihood would estimate.</p> | 69,876 |
<p>Does it ever make sense to compare the variance for two sets of data, neither of which are even approximately normal (e.g. bimodal)?</p> | 30,536 |
<p>I conducted listening experiment in which 16 participants had to rate the audio stimuli along 5 scales representing an emotion (sad, tender, neutral, happy and aggressive). Each audio stimulus was synthesized in order to represent a particular emotion. Participants had to move 5 sliders each of which corresponded to... | 69,877 |
<p>I was going to build an ANCOVA model with two treatment groups (climbed/unclimbed) and a set of 10 potential environmental covariates which may collectively remove the significance of the climbing treatment, if environmental factors are correlated with the treatment groups (there is uncertainty here because the samp... | 14,095 |
<p>Both functions are great for comparing, for example, survival models. The first especially for computing Harrell's C-index, the second for NRI and IDI.</p>
<p>However, it looks like <code>rcorr.cens</code> takes survival probabilities and <code>improveProb</code> takes event probabilites, that is, 1 - survival prob... | 69,878 |
<p>I've got a dataset for Temperature & KwH and I'm currently performing the regression below. (further regression based on coeffs is performed within PHP)</p>
<pre><code># Some kind of List structure..
UsageDataFrame <- data.frame(Energy, Temperatures);
# lm is used to fit linear models. It can be used to ca... | 30,541 |
<p>I have a bunch of genetic read counts for different several genes. Each gene is divided into two groups (0 and 1). What I want to do is make a vertical plot side by side of the 0 group and the 1 group. Thus if there were 10 observations in the zero group and 20 observations in the 1 Group, there would be 10 dots in ... | 69,879 |
<p>I have been looking into problem of sentence segmentation lately. I have been referring to NLTK's book for this purpose. I followed their procedure to segment sentences presented here:
<a href="http://www.nltk.org/book/ch06.html" rel="nofollow">http://www.nltk.org/book/ch06.html</a> (Section 6.2)</p>
<p>I used all ... | 69,880 |
<p>Assume I have a dataset for a supervised statistical classification task, e.g., via a Bayes' classifier. This dataset consists of 20 features and I want to boil it down to 2 features via dimensionality reduction techniques such as Principal Component Analysis (PCA) and/or Linear Discriminant Analysis (LDA).</p>
<p>... | 30,547 |
<p>I have never been so confused in my life. Could anyone please tell me what is the difference between the following mixed effects models:</p>
<pre><code>mdl1<-lme(y ~ x,random=~1|state,method="ML",data=df) # does this allow intercepts to vary across States but keeping the slope fixed (i.e. relationship between y ... | 69,881 |
<p>While I was preparing an internet survey, I read from multiple sources which says it is more important to have a high response rate than large sample size.</p>
<p>Q1. I don't quite understand the logic behind this. Can you explain? If i can afford to survey the entire population, would that be better than a random ... | 69,882 |
<p>I've recently completed a project where I used scikit-learn's <code>DBSCAN</code> module to find clusters in relatively short strings of text. I used a custom string similarity metric to allow for vectorized computation of an n<sup>2</sup> similarity matrix.</p>
<p>I know that it is possible to reduce the time comp... | 69,883 |
<h2>Background</h2>
<p>As I understand it (as a novice), parametric tests don't use your actual data as input but rather parameters extracted from your data which describe a distribution. The tests use the distributions which are modelled on your data.</p>
<p>Many researchers who have a limited understanding of the t... | 30,548 |
<p>I am confused about how to partition the data for k-fold cross validation of ensemble learning.</p>
<p>Assuming I have an ensemble learning framework for classification. My first layer contains the classification models, e.g. svm, decision trees.</p>
<p>My second layer contains a voting model, which combines the p... | 30,549 |
<p>I am learning ML. I have encountered a lot probability density functions. I want to use MATLAB to illustrate them. For example,the density function of the Normal distribution function in two dimensions:</p>
<p>$$p(\vec{x};\mu,\Sigma) = \frac{1}{2\pi \sqrt{\det(\Sigma)}}\exp\left(-\frac{1}{2}(\vec{x}-\mu)^T\Sigma^{-... | 30,550 |
<p>I try to implement a time series data analysis project, but I have to do in Java, C# or Python, is there any good libary such like LOESS, ARIMA in R you can recommend? Many thanks</p> | 47,839 |
<p>I do have an issue with libSvm Weka which i feel it is very weird </p>
<p><img src="http://i.stack.imgur.com/4EabI.png" alt="Confusion Matrix"><img src="http://i.stack.imgur.com/jtNeQ.png" alt="Statistics"></p>
<p>However, when i tried it with other algorithms such as naive bayes and j48, it achieved a high accura... | 30,551 |
<p>I have the following image which I've been told is an illustration of how the posterior probability distribution is a combination of the prior and likelihood distributions. </p>
<p><img src="http://i.stack.imgur.com/6avEH.png" alt="enter image description here"></p>
<p>I've been told that there's something wrong w... | 32,419 |
<p>I have an experiment where people click on different ads online. My measure is click counts.</p>
<p>I end up finding that I should use models for count data such as Poisson, Quasi-Poisson, or Negative Binomial regression.</p>
<p>Is there a standard in marketing regarding what model should be used for click counts?... | 69,884 |
<p>Random forests are well known to perform fairly well on a variety of tasks and have been referred to as the <a href="http://blog.yhathq.com/posts/random-forests-in-python.html" rel="nofollow">leatherman of learning methods</a>. Are there any types of problems or specific conditions in which one should avoid using a ... | 69,885 |
<p>This question has been triggered by something I read in this graduate-level statistics textbook and also (independently) heard during this presentation at a statistical seminar. In both cases, the statement was along the lines of "because the sample size is pretty small, we decided to perform estimation via bootstra... | 30,554 |
<p>Am not so good with econometrics but I have to estimate two equations with Fe and Re. I have 8 vars which translate to 6,006 obs. the problem is that all the p-values are higher than 5%, does this mean the resgressors cant explain anything about the dependent var?</p> | 30,555 |
<p>Is this a feasible thing to do? I've mostly seen the proxy variable approach used for dealing with omitted variable bias and measurement error. But how would one go about using it for simultaneity?</p>
<p>Say in the classic example: Crime rate=pop.density+income+....+police/capita+e</p>
<p>where police/capita and ... | 69,886 |
<p>Is there any way to test the difference of entropy given frequency table?</p>
<p>For example, let's say we have dice 1 and dice 2,</p>
<p>and we experimented with them and they showed up like</p>
<pre><code> die 1
num. 1 2 3 4 5 6
freq 6 7 3 5 2 1
die 2
num. 1 2 3 4 5 6
freq ... | 69,887 |
<p>How is the $A(\cdot) = \int\frac{du}{V^{1/3}(\mu)}$ normalizing transform for the exponential family derived? </p>
<p>More specifically: I tried to follow the Taylor expansion sketch on page 3, slide 1 of <a href="http://bit.ly/VtM1UR" rel="nofollow">http://bit.ly/VtM1UR</a> but have several questions. With $X$ fr... | 69,888 |
<p>Suppose one performs the so-called non-parametric bootstrap by drawing $B$ samples of size $n$ each from the original $n$ observations with replacement. I believe this procedure is equivalent to estimating the cumulative distribution function by the empirical cdf:</p>
<p><a href="http://en.wikipedia.org/wiki/Empiri... | 69,889 |
<p>The two parameters of DBSCAN are epsilon and minimum samples. Shouldn't epsilon be called like "Circle radius"? Why is it called epsilon?</p> | 30,556 |
<p>The log density of a multivariate Gaussian is proportional to $||x-\mu||_2^2$, i.e. the norm of the difference between $x$, the random variable, and $\mu$, the mean of the distribution (assuming a covariance matrix of the form $\sigma^2 I$).</p>
<p>Gaussians are defined with $L_2$ norm. What about the general case ... | 69,890 |
<p>I have an experiment that produces one measurement every time it is run. I can change something in the experimental setup, and I want to test if this change in the setup results in a change of the measured value. I am repeating the measurement multiple times for each setup, but only one measurement with one setup ca... | 69,891 |
<p>Say I have three independent events with a probability of .25, .5, and .75 chance success for the individual events. How would I determine the probability that 0, 1, 2, or 3 of the events are successful?</p> | 49,838 |
<p>I have a 0/1 sparse matrix with 500 k columns and 3 M rows and I want to do reduce the number of columns.</p>
<p>Clearly I cannot load this into <code>R</code>, as is, so <code>prcomp</code> is out.
(I cannot even create the Gram matrix in <code>R</code>: <code>too many elements specified</code>.)</p>
<p>However, ... | 30,557 |
<h1>Business Problem</h1>
<p>We are measuring the duration of an operation on our server. We want to know if certain changes (call them treatments) make this operation faster or slower.</p>
<h1>Data</h1>
<p>Our current test harness is outputting data every 3 seconds. During those 3s it is collecting a large number o... | 40,899 |
<p>Sorry if Im missing something very obvious here but I am new to mixed effect modelling. </p>
<p>I am trying to model a binomial presence/absence response as a function of percentages of habitat within the surrounding area. My fixed effect is the percentage of the habitat and my random effect is the site (I mapped 3... | 30,558 |
<p>My biologist friend is having a bad time with her experiment. It's suspected that changing the temperature and organic content in water may affect the growth of crustaceans. In her experiment, two formulations of different organic content combined with four different temperatures (plus control) were combined. 10 tin... | 69,892 |
<p>When working with probit models in stata the first line of the output is (for a sample of 583 with 3 variables): </p>
<p>Iteration 0: log likelihood = -400.01203</p>
<p>If I understand this correctly the iteration 0 is the log likelihood when the parameter for my 3 variables = 0. </p>
<p>The log likelihood func... | 69,893 |
<p>I'm working on a project and I haven't quite figured out the best way to analyze the data. Any help would be much appreciated. </p>
<p>Design:
Dependent variable: variable A measured at time 1 only.
Independent variables: variable B and variable C measured 14 times longitudinally</p>
<p>Goal: Predict variable A f... | 69,894 |
<p>I am new to R. I am trying to apply forecasting model Time Series (TS) Model
as follows: </p>
<ol>
<li>Plotting original data, </li>
<li>Simple Moving Average, </li>
<li>Auto correction(AC), Partial AC, Differencing of TS etc to get stationary time series, </li>
<li>Fitting optimal model which gives minimum AIC,... | 11,943 |
<p>So classic regression methods (ridge regression, LASSO) only predict the posterior mean $E[ Y | X ]$, while Gaussian Processes give you the full posterior distribution $Y | X$. </p>
<p>It would be very useful if the posterior distribution had low variance in regions where the posterior mean is actually close to the... | 30,560 |
<p><strong>Question:</strong>
for $x_1...x_n \sim Pois(\lambda)$</p>
<ol>
<li><p>Find a CI for $\lambda$ (using the MLE).</p></li>
<li><p>Find a CI for $\psi=\sqrt \lambda$</p></li>
</ol>
<p><strong>What I did:</strong></p>
<p>On 1, I found that the MLE is $\bar x$ and then using the normal approximation (the only t... | 69,895 |
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