question stringlengths 37 38.8k | group_id int64 0 74.5k |
|---|---|
<p>Greetings,</p>
<p>Currently I'm doing the following in R:</p>
<pre><code>require(zoo)
data <- read.csv(file="summary.csv",sep=",",head=TRUE)
cum = zoo(data$dcomp, as.Date(data$date))
data = zoo(data$compressed, as.Date(data$date))
data <- aggregate(data, identity, tail, 1)
cum <- aggregate(cum, identity... | 70,399 |
<p>Before starting an a/b test with a control and one experimental route, I can calculate a required sample size based on conversion rate estimates for both routes. I can get a good estimate of the conversion rate of the control by looking at historical data. But the conversion rate of the experimental route is unknown... | 31,333 |
<p>In longitudinal studies, you might be observing time-to-event endpoints with some covariate that changes as a function of time. When covariates are fixed at baseline, the only independence assumption involved is within the risk set, or the collective at risk observed during event times. Otherwise, the fact that an i... | 70,400 |
<p>These static cumulative default rate tables and charts come from <a href="http://www.fitchratings.com.ar/uploads/kcri0908.pdf" rel="nofollow">this public report</a> published by a credit rating agency.</p>
<p>Basically, you take all the loans originated in a period of time (a "vintage") and track the cumulative am... | 37,233 |
<p>Suppose that I have a market research survey with the question "What brand of television are you planning on buying" and then also have a choice that is "I don't plan on buying a television." Respondents may choose more than one brand, but they may not make any other choices if they select that they do not plan on ... | 70,401 |
<p>Take a study that collects subjective guesstimates as a proxy for some variable, like the quality of service. In a simplest model, we then regress the monthly sales on these guesstimates. How to interpret the results given that they originate from subjective estimations?</p>
<p>One problem is that respondents have ... | 70,402 |
<p>In a multiple linear regression it is possible to find out the coeffient with the following formula.</p>
<p>$b = (X'X)^{-1}(X')Y$</p>
<pre><code>beta = solve(t(X) %*% X) %*% (t(X) %*% Y) ; beta
</code></pre>
<p>For instance:</p>
<pre><code>> y <- c(9.3, 4.8, 8.9, 6.5, 4.2, 6.2, 7.4, 6, 7.6, 6.1)
> x0 &l... | 31,336 |
<p>I've never liked how people typically analyze data from Likert scales as if error were continuous & Gaussian when there are reasonable expectations that these assumptions are violated at least at the extremes of the scales. What do you think of the following alternative:</p>
<p>If the response takes value $k$ o... | 70,403 |
<p>Disjoint events A and B with positive probability must not be independent as $P(A)$, $P(B) \gt 0$, $P(A\cap B) = P(\emptyset) = 0 \Rightarrow P(A\cap B) \lt P(A)P(B)$. What are some real world examples that can help better understanding this?</p> | 31,338 |
<p>I am starting to learn R and its power for giving survival predictions.</p>
<h3>Abstract</h3>
<p>I use the <code>predictSurvProb</code> function from the <code>pec</code> package to get predicted survival risks. My data has 5000 rows wherein each thousand falls into a certain <code>time</code> category. These <cod... | 37,251 |
<p><img src="http://i.stack.imgur.com/0jywZ.png" alt="enter image description here"></p>
<p>I am trying to fit a model for the values plotted above. The explanatory variable represents amounts of compensation claim in an earthquake, and the response variable represents amounts of compensation awarded. Can someone tell... | 70,404 |
<p>I want to know is their any possible way to calculate Jaccard coefficient using matrix multiplication.</p>
<p>I used this code </p>
<pre><code> jaccard_sim <- function(x) {
# initialize similarity matrix
m <- matrix(NA, nrow=ncol(x),ncol=ncol(x),dimnames=list(colnames(x),colnames(x)))
jaccard ... | 70,405 |
<p>I am trying to reproduce the results from <a href="http://stats.stackexchange.com/a/14773/2798">this answer</a> in CrossValidated with no luck. I keep getting an error when calling: </p>
<pre><code>print("Fitting Penalized Linear Model")
GLMmodel <- train(X,Y,method='glmnet',trControl=myCtrl,tuneLength=10)
</cod... | 70,406 |
<p>I was attempting a self-study question on the normal distribution, but I wasn't able to get to the answer. I'm not sure if my method used here is incorrect, and would appreciate some guidance and advice.</p>
<p><strong>Question</strong></p>
<blockquote>
<p>The pulse rate per minute of the adult male population b... | 70,407 |
<p>I was attempting to solve a question on finding the probability that a randomly selected person had an income of $50,000 or more would be audited, based on information on the table below:</p>
<p><img src="http://i.stack.imgur.com/0aTNw.jpg" alt="enter image description here"></p>
<p>My attempt was to take the prop... | 70,408 |
<p>If you were to take random positive integers, put them into a list, and sort them is there anyway to find the expected value of the kth item in the list? The list is sorted in ascending order. </p>
<p>By random positive integer I mean some number in the range 0-N where the probability of each number occurring is eq... | 70,409 |
<p>I have a set of data where the response is a proportion. For each event in the experiment, a system will correctly tag <code>X</code> of <code>Y</code> items. In the end, I will have something like 100 different results. I have been trying to determine what is the most correct method of fitting the response varia... | 31,342 |
<p>I want to explore whether attitudes mediate the relationship between employment status and intention to apply to graduate school. (See image below).</p>
<p>I planned to use the Sobel Test to explore the mediation, but I'm not sure I can. How does one/how can one test for mediation with a categorical predictor and ... | 917 |
<p>What are theoretical reasons to not handle missing values? Gradient boosting machines, regression trees handle missing values. Why doesn't Random Forest do that?</p> | 70,410 |
<p>I do not have enough knowledge about optimization.
My problem is simple. </p>
<p>Lets say I have 100 classes. Each class contains some instances (images). The feature vector obtained from a particular image depends on a parameter P.</p>
<p>I need to learn this parameter automatically by maximizing the classificati... | 70,411 |
<p>I've recently been wondering how to visualise a linear model with >1 predictor. Today I came across a paper that managed to visualise a linear model with 6 predictors (and one response variable) in a scatterplot. </p>
<p>The model was similar to this:</p>
<p>weight ~ days since 1st Sept + site + age + year + PC1 +... | 70,412 |
<p>I am applying some chaos tests in financial time series in R and I am interested to run a NEGM (Nychka, Ellner, Gallant, McAffrey) Test for a largest Lyapunov exponent based on Jacobian methods. Do you know any package that contains this test, or at least some implementation?</p> | 70,413 |
<p>I am working on some GWAS (Genome-Wide Association Studies) now. A genome scan was done for all the SNPs, with first 3 principal components adjusted (PCs are used for adjusting ethnicity effect) and the QQ plot looks fine (most p-values lay on the diagonal line with a few signals off the line). </p>
<p>However, whe... | 31,346 |
<p>I'm reading through the Gaussian Process book <a href="http://www.gaussianprocess.org/gpml/chapters/RW2.pdf" rel="nofollow">http://www.gaussianprocess.org/gpml/chapters/RW2.pdf</a> and there's one section here I don't quite understand (page 11). The author says:</p>
<blockquote>
<p>"the predictive distribution is... | 47,997 |
<p>Can someone please tell me the difference between the kernels in SVM: </p>
<ol>
<li>Linear </li>
<li>Polynomial </li>
<li>Gaussian (RBF)</li>
<li>Sigmoid </li>
</ol>
<p>Because as we know that kernel is used to mapped our input space into high dimensionality feature space.
And in that feature space, we find t... | 31,348 |
<p>I have a relatively small sample ($N = 64$) with the following variables:</p>
<ul>
<li><code>ScoreA_I</code>: continuous pre-test response variable </li>
<li><code>ScoreA_II</code>: continuous post-test response variable </li>
<li><code>ScoreB_I</code>: continuous pre-test response variable </li>
<li><p><code>S... | 70,414 |
<p>Assume a scalar random variable $X$ belongs to a vector-parameter exponential family with p.d.f.</p>
<p>$$ f_X(x|\boldsymbol \theta) = h(x) \exp\left(\sum_{i=1}^s \eta_i({\boldsymbol \theta}) T_i(x) - A({\boldsymbol \theta}) \right) $$</p>
<p>where ${\boldsymbol \theta} = \left(\theta_1, \theta_2, \cdots, \theta_s... | 31,350 |
<p>I am building a database schema for a web application that will collect user feedback on restaurants. As the collection of user feedback grows for each restaurant, I will be analyzing it to assign properties to the restaurant record that will be exposed publicly in the web app. Some example processing algorithms I p... | 70,415 |
<p>I've got a dataset where stations (3) are nested within beaches (5). Every station is replicated 6 times per beach, so that I have a total of 90 observations.</p>
<p>I now want to test for equal variances, so I chose the Bartlett test in R. I somehow got myself confused; what would be my reference variable for my v... | 70,416 |
<p>let $x_{1},..,x_{n}$ be iid with cauchy distribution.
Let $y=median(x_{1},..,x_{n})$ , $z=MLE$. I get that $y$ is not an asymptotically efficient estimator to the location of a cauchy distribution because the asymptotic approximation to the distribution of the sample median has variance ${\pi}^2/4$ and minimum varia... | 70,417 |
<p>I am trying to train a regression model for dataset with 500k observations and 3 features. The features are categorical and have 50, 50 and 100 levels.</p>
<p>Is (generally) kNN appropriate for this kind of task?</p>
<p>I am using R. I tried to turn my categorical variables into dummy variables but I end up with v... | 31,352 |
<p>In my introductory book on time series analysis the backshift operator $\mathbf{B}$ is introduced using the following definition:
$$
\mathbf{B}x_t=x_{t-1}
$$
Then the author sets off to derive some properties of random walks, and there is this step, that is a complete mystery to me:
$$
x_t=(1-\mathbf{B})^{-1}w_t\Rig... | 70,418 |
<p>I have binomial outcome data for three groups that I am analyzing with Cochran's Q test. As discussed at this site, <a href="http://yatani.jp/HCIstats/Cochran" rel="nofollow">Cochran</a>. </p>
<p>However, I have to repeat this seven different times because I am analyzing performance of three diagnostic tests to s... | 31,356 |
<p>I have a small dataset of n = 200 with about 80 predictors. The outcome I am working with is binary. I'm interested in doing a two-step process where:</p>
<p>(1) I conducted recursive feature extraction using random forests to pull out the predictors that maximize predictive ability.</p>
<p>(2) Examining that subs... | 70,419 |
<p>I've read about the <a href="https://en.wikipedia.org/wiki/Approximate_Bayesian_computation" rel="nofollow">ABC rejection</a> algorithm when not being able to calculate the likelihood directly, and my question is: if we have to introduce a distance measure $\rho(D,D')$ anyways, why not use that measure as a pseudo-l... | 31,357 |
<p>I have data clustered in various sets whose amount of member variables and occupied area varies, the former among multiple magitudes. </p>
<p>Here is an <strong>example</strong>:</p>
<p><em>Set A is very concentrated and has 100000 Elements.
Set B is slightly more widespread and contains 1000 Elements.
Set C is co... | 37,661 |
<p>I got into a discussion with a colleague today about some of our data sensors. Our sensors weigh objects anywhere from 10 to 100 tonnes. currently we calculate the error as:</p>
<p>$$
error = \frac{\left (x_{field} - x_{true} \right )}{x_{true}}
$$</p>
<p>The problem is that if the error is consistent in terms of... | 31,359 |
<p>I have 3 within-subject factors, namely <code>offset</code> (1px, ..., 5px), <code>side</code> (left, right) and <code>color</code> (red, green), which define the characteristics of the stimulus in a reaction time experiment. The DV is reaction time <code>RT</code>. The design is fully balanced. </p>
<p>I ran a rep... | 70,420 |
<p>I've been told (read) this many times, but I never understood why it's bad for the number of dimensions in your data, or the number of explanatory variables in your model to be higher than your number of samples. Why is this the case?</p> | 70,421 |
<p>Suppose we have three absolutely continuous random vectors $X, Y, Z$. Can anyone prove the following formula?</p>
<p>$$X|(Y,Z) =(X|Y)|(Z|Y)$$
Put differently $p(X|Y,Z)=p(\hat{X}|\hat{Z})$, where $\hat{X}=X|Y$ and $\hat{Z}=Z|Y$.</p>
<p><strong>Example of use</strong></p>
<p>I want to determine distribution of $X|(... | 70,422 |
<p>For example:</p>
<pre><code>k <- 100
R <- 10000
max.g <- numeric(R)
for(i in 1:R) max.g [i] <- max(rnorm(k))
hist(max.g) # We can see it's right tailed...
</code></pre>
<p>I remember once encountering that there is a name for this type of distributions, but the name alludes me.</p> | 749 |
<p>I am looking for a fractal-based statistical measure which could be used as alternative to correlation between two variables (I know that hurst exponent can be used for auto-correlation).</p>
<p>Is anyone aware of such measures?</p> | 31,364 |
<p>I'm performing a "dynamic" market basket analysis where a customer transaction is traced from the beginning (here it has an initial basket of product) to the finalized purchase (where there is the final basket) but he can change the items in the basket time by time and it is all traced. How can I model such dynamics... | 10 |
<p>In this paper on p315:</p>
<p><a href="http://www.ssc.upenn.edu/~fdiebold/papers/paper55/DRAfinal.pdf" rel="nofollow">http://www.ssc.upenn.edu/~fdiebold/papers/paper55/DRAfinal.pdf</a></p>
<p>They explain that they use Levenberg Marquardt (LM) (along with BHHH) to maximize the likelihood.
However as I understand i... | 70,423 |
<p>In my survey, I had a question that asked respondents why they did NOT engage in a particular behavior (x). Some of the answers were stated in a positive way, such as "because of age" while some were stated in a negative way "I did NOT know how to do x". </p>
<p>I am trying to reverse code because I am using these ... | 70,424 |
<p>I ran <code>lm()</code> (I'm using R, but I don't think anything else in this question is R specific) then realized I'd used the wrong input data, basically meaningless. Yet, I got a really good model:</p>
<pre><code>Residuals:
Min 1Q Median 3Q Max
-0.069654 -0.003899 -0.000381 0.0047... | 70,425 |
<p>I have a classification problem with 2 classes. I have nearly 5000 samples, each of which is represented as vector with 570 features. The positive class samples are nearly 600. Meaning, I have a 1:8 ratio of positive and negative samples in the dataset. This imbalance in the dataset is mitigated using <a href="http:... | 70,426 |
<p>I'm running some multiple group CFA models comparing covariance structure by race/ethnicity and have survey data from 6th, 8th, 10th and 12th graders. My supervisor has told me to combine 6th and 8th grade to run a middle school only model and to combine 10th and 12th grade for a high school only model. This makes... | 70,427 |
<p>Assume I have a small sample size, e.g. N=100, and two classes. How should I choose the training, cross-validation, and test set sizes for machine learning?</p>
<p>I would intuitively pick</p>
<ul>
<li>Training set size as 50</li>
<li>Cross validation set size 25, and</li>
<li>Test size as 25.</li>
</ul>
<p>But p... | 70,428 |
<p>Please can you help me, with this question:</p>
<p>Let $X$ be a random variable with a distribution $P_\theta$ in $\{P_\theta : \theta \in \Theta\}$, $f_\theta$ be the p.d.f of $P_\theta$ w.r.t a measure $\nu$, $A$ be an event, and $\mathcal{P}_A=\{f_\theta I_A/P_{\theta} (A): \theta \in \Theta\}$.</p>
<ul>
<li><p... | 70,429 |
<p><strong>Context:</strong> The variance of a sum of independent random walks is a sum of their variances: $\sigma^2 = \sigma_1^2 + \sigma_2^2$. In case of a dependent random walks with bivariate normal distribution it will be $\sigma^2 = \sigma_1^2 + \sigma_2^2 + 2 \rho \sigma_1 \sigma_2$.</p>
<p><strong>Question:</... | 31,369 |
<p>Having the Netflix challenge in mind: collaborative filtering is typically presented as a matrix dimension reduction. </p>
<p>My question is how does the problem relate to classical regression (supervised learning) problems? Can it be seen as an instance of these or does it differ in some fundamental way?</p> | 70,430 |
<p>Can anyone explain principal component regression with the help of an example and the code in R? How to interpret the result of a principal component regression? How to find the individual effect of independent variables on dependent variable in case of PCA since we deal with components?</p> | 70,431 |
<p>I am working with R, doing a post-hoc power analysis.</p>
<p>Can anyone explain to me why these two commands generate different outputs? I thought they should not!</p>
<pre><code>> 1-pt(tcrit-nc, df)
[1] 0.4248602
> 1-pt(tcrit, df, ncp=nc)
[1] 0.430632
</code></pre>
<p>I've got ...</p>
<pre><code>n = 18
df... | 70,432 |
<p>I have read the articles of both of these statistical methods on wikipedia, and as far as I can tell they are used in the same cases. I could not tell in how far they work the same way, since the <a href="https://en.wikipedia.org/wiki/Two-way_analysis_of_variance" rel="nofollow">two-way ANOVA article</a> is rather e... | 70,433 |
<p>I am currently doing a short term forecast using ARIMA model.I have been following Box and Jenkins method and to choose the best ARIMA parameters to do do my forecast I tested various(p,q) combinations and took the one with the lowest aic(akaike information criteria). I assigned a d value as the number of differenci... | 70,434 |
<p>When using the survey procs in SAS on imputed dated, is it best to include the
imputation variable on the table or domain statement, or should it be
included on the by statement? I found one paper
(<a href="http://support.sas.com/resources/papers/proceedings10/265-2010.pdf" rel="nofollow">http://support.sas.com/... | 70,435 |
<p>I have a set of 50 million text snippets and I would like to create some clusters out of them. The dimensionality might be somewhere between 60k-100k. The average text snippet length would be 16 words. As you can imagine, the frequency matrix would be pretty sparse. I am looking for a software package / libray / sdk... | 9,031 |
<p>Trying to teach myself R and found the following conundrum. I wrote a script to simulate rolling a die and adding the value until a "1" is rolled. This worked well (eventually). The mean and variance matched with the theoretical (1-p)/p. I took one of the runs of 1000 samples and tried to fit a geometric distrib... | 70,436 |
<p>Is there alternative / replacement in Python of Factorie (<a href="http://factorie.cs.umass.edu/index.html" rel="nofollow">http://factorie.cs.umass.edu/index.html</a>) - In particular I am looking for a tool in Python that allows me to create arbitrarily structured CRFs for a custom NER task. </p>
<p>I have found <... | 70,437 |
<p>When I use bootstrapping (updating the negative samples generated by existed classifier model and then retraining classifier model for next round; And do this for several rounds) in machine learning, I find that after several round (maybe 10 rounds), the result come to converge and stable even if the classifier mode... | 70,438 |
<p>I have become interested in statistics, but I must admit that it has been a long time since I have used math seriously. Sometimes I understand what equations mean, but sometimes I can't follow them.</p>
<p>I like the answer given here that uses the image with an arrow: <a href="http://stats.stackexchange.com/quest... | 41,903 |
<p>In the spirit of <a href="http://stats.stackexchange.com/questions/114/what-statistical-blogs-would-you-recommend">What statistical blogs would you recommend?</a> I propose a collection of machine learning blogs worth reading.</p> | 70,439 |
<p>I'm training a Multi-class LDA classifier with <strong>8 classes</strong> of data.</p>
<p>While performing training, I get a warning of: "<strong>Variables are collinear</strong>"</p>
<p>I'm getting a <strong>training</strong> accuracy of over <strong>90%</strong>.</p>
<p>I'm using <strong>scikits-learn</strong> ... | 70,440 |
<p>Consider multivariate time series models that estimate potentially time-varying conditional means, variances, and correlations (one type of model might be a VAR(p)+Garch(1,1)+DCC Gaussian Copula model). I will simulate from one "true" distribution and compare other potential models to it. I don't particularly care a... | 31,384 |
<p>I see these terms being used and I keep getting them mixed up. Is there a simple explanation of the differences between them?</p> | 31,385 |
<p>I have a set of points that I want to cluster into groups according to a number of features computed.</p>
<p>I have distance matrix containing the distances between all different pairs of points. I have tried K-Means, and DBSCAN first but since I have no clue about that number of clusters underlying in the data, r... | 31,386 |
<p>I got these results from a GLM from R, but I am not sure what it means that the intercept is significant but none of my variables actually are. So is nothing really significant? Here are my results:</p>
<pre><code>Groups Name Variance Std.Dev. Corr
Plot (Intercept) 1.4842e+07 3852.4696
... | 31,387 |
<p>In Andrew Ng's <a href="http://www.youtube.com/playlist?list=PLA89DCFA6ADACE599">machine learning course</a>, he introduces linear regression and logistic regression, and shows how to fit the model parameters using gradient descent and Newton's method.</p>
<p>I know gradient descent can be useful in some applicatio... | 70,441 |
<p>In engineering, we usually have Handbooks that pretty much dictate the state of the practice. These books are usually devoid of theory and focus on the applied methodology. Is there a forecasting Handbook out there? that solely focuses on the technique and not the background?</p> | 70,442 |
<p>I have a 2-way repeated measures design (3 x 2), and I'd like to get figure out how to calculate effect sizes (partial eta squared).</p>
<p>I have a matrix with data in it (called a) like so (repeated measures)</p>
<pre><code> A.a A.b B.a B.b C.a C.b
1 51... | 49,849 |
<p><strong>A</strong>. Determine the restrictions needed on the $a$'s so that $z=\sum_{i=1}^{n}a_iX_i$ will be an unbiased estimator $E\left[X\right]$, where $X_1,X_2,\dotsc,X_n$ represents a random sample of $X$.</p>
<p><strong>Answer:</strong> The $a$'s must sum to one.</p>
<p><strong>B</strong>. What is the best s... | 41,908 |
<p>NOTE: I am using Stata for doing this.</p>
<p>I have a long panel dataset, meaning my N is much smaller than my T. I have N = 5, T = 61. I tried to estimate my model, but I get an error related to the fact that I do not have enough degrees of freedom for calculating as many variables as I have.</p>
<p>This is wh... | 70,443 |
<p>I'm trying to determine the effects of four treatments on flowers on the volume of nectar available to pollinators. Problem is, I have about 50% zero volumes across treatment categories. What is the best approach to comparing mean volumes between treatments? </p> | 70,444 |
<p>I'm very new to <strong>R</strong> and PLS-regression. I would like to know, based on your experience, which <strong>R</strong> packages for PLS-regression are most highly recommended. My area of application is chemistry.</p> | 18,174 |
<p>I'm using the function <code>gstslshet</code> from the package <code>sphet</code> in R, but I'm wondering what the outcome is. Is it a model which can be used to make new predictions? I've put my summary output below (I am new to this kind of modelling).</p>
<pre><code> Generalized stsls
Call:
gstslshet(formula = ... | 70,445 |
<p>I am looking at a model trained with <a href="http://arxiv.org/abs/1312.6114" rel="nofollow">stochastic gradient variational Bayes</a>. In <a href="http://arxiv.org/abs/1401.4082" rel="nofollow">this paper</a> an importance sampler is proposed to estimate the likelihood:</p>
<p>$$p(x) \approx {1 \over S} \sum_{s=1}... | 31,398 |
<p>I have a Dirichlet distribution from which I'm maximizing $\alpha$ by calculating the log likelihood with the following equation</p>
<p>$p\left(s|\alpha\right) = \sum\limits_{i=1}^O\log\left(\frac{n_i!}{\prod\limits_{j=1}^kn_{ij}!}\frac{\Gamma\left(\alpha_0\right)}{\Gamma\left(\sum\limits_{j=1}^k\left(n_{ij}+a_j\ri... | 70,446 |
<p>Does anyone know anything about the distribution of a random vector divided by it's norm? More specifically, if we know the distribution of a vector valued random variable $x$, what can we say about the distributions of $\frac{\vec{x}}{||\vec{x}||_2}$ and $\frac{\vec{x}}{||\vec{x}||^2_2}$ </p>
<p>1) In general</p>... | 70,447 |
<p>I'm wondering when it is possible to distinguish between a data generating process that is missing at random (MAR) vs one that is not missing at random (NMAR) by analyzing a directed acyclic graph (DAG). For example, suppose we have the following: </p>
<p>$$
\begin{matrix}
T& \longrightarrow & Y \\
\downa... | 70,448 |
<p>I hope this is the appropriate venue for this type of question. If not, please feel free to migrate! :)</p>
<p>I'm trying to solve a stochastic partial differential equation of the form $$\alpha(\omega)\nabla^2u=f$$
where $\alpha(\omega)$ represents a random field that is log-normally distributed, i.e. it has a pr... | 70,449 |
<p>I am confused about the exact definitions here.</p>
<p>Assuming I have a cross-sectional regression, let's say, Wage on Education and I additionally control for observable characteristics with a set of dummies or variables like intelligence level, age, parent's education level, urbanization area, gender, race, work... | 70,450 |
<p>The chi square formula given in my book is:</p>
<p>$\chi^2 = \frac{(n-1)s^2}{\sigma^2} $ </p>
<p>At first I admitted to feeling some kind of strangeness to this formula, but after a few hours I realized that $\chi^2$ was $\displaystyle \sum_{i=1}^n \left(\frac{X_i - \mu}{\sigma}\right)^2 - \left( \frac{\bar{x} - \... | 31,401 |
<p>In finance, two procedures are sometimes used to help evaluate the likelihood that positive results were obtained strictly due to data mining:</p>
<ul>
<li>White's Reality Check (WRC), described in White's 2000 Econometrica paper</li>
<li>Monte Carlo Permutation (pair matching of historical data with signals withou... | 41,921 |
<p>An assumption of the ordinal logistic regression is the proportional odds assumption. Using R and the 2 packages mentioned I have 2 ways to check that but I have questions in each one.</p>
<p>1) Using the rms package</p>
<p>Given the next commands</p>
<pre><code>library(rms)
ddist <- datadist(Ki67,Cyclin_E)
op... | 70,451 |
<p>The approximation to the function max(x) can be written as a NOISY-OR as given below: $ max_k(x) = 1-\prod_k(1-x) $</p>
<p>Are there any way to approximate min(x) ?</p> | 70,452 |
<p>My first post in this useful community. Ive been trying to use GLS methods in non-linear mixed effects models and have found this post, <a href="http://stats.stackexchange.com/questions/14426/prediction-with-gls">Prediction with GLS</a> extremely informative and helpful.
Some of my questions are probably more of a ... | 31,404 |
<p>Which type of test is most appropriate for this comparative-descriptive study? I have two groups of subjects (250 in each). My goal is to determine if the two subject groups are different and if so, how. I'm using an online survey of 50 statements (embedded are 5 statements about 10 different possible factors). Sub... | 41,925 |
<p>I am interested to know how to calculate the joint probability mass function for two independent geometric random variables. </p>
<p>Suppose two variables X1 and X2 are independent, such that <code>Xi∼Geometric(theta)</code>, how to find the joint pmf distribution of X1 and X2. I am not sure but I think it should b... | 70,453 |
<p>In my data I have 9 different sets of data for 2 different groups. Each one of these datasets is the same measurement changing over the time. If I make a graph, I can see 9 lines for each group.
I did an average of the 9 lines for each group, and I can get 2 lines with SD and N, one for each group. </p>
<p>How do I... | 70,454 |
<p>This question is sort of general and long-winded, but please bear with me.</p>
<p>In my application, I have many datasets, each consisting of ~20,000 datapoints with ~50 features and a single dependent binary variable. I am attempting to model the datasets using regularized logistic regression (R package <a href="h... | 70,455 |
<p>I am implementing statistical analysis in a C# program and am using the <a href="https://controls.engin.umich.edu/wiki/index.php/Design_of_experiments_via_taguchi_methods%3a_orthogonal_arrays" rel="nofollow">Taguchi Method</a> to do it (the Taguchi arrays are about a 1/4th of the way down the page).</p>
<p>The arti... | 70,456 |
<p>Am trying to solve a system of linear equations involving three variables using <code>R</code>. However, I get an error as shown below:</p>
<pre><code>> A = matrix(data=c(-0.4, 0.4, 0.15, 0.3, -0.55, 0.6, 0.1, 0.15, -0.75), nrow=3, ncol=3, byrow=TRUE)
> A
[,1] [,2] [,3]
[1,] -0.4 0.40 0.15
[2,] 0.3 ... | 41,929 |
<p>I've got a large number of calibration curves (i.e. instrument response vs. analyte concentration), and I'd like to check whether they are different from each other.</p>
<p>Exactly one curve is associated with each unique combination of the levels of two factors (day and treatment). So, in R, the data look like thi... | 70,457 |
<p>Suppose I am entered into a <a href="http://diablo3acts.com/" rel="nofollow">contest</a>, with the following rules:</p>
<ul>
<li>Every person may get up to 6 entries</li>
<li>All the entries will be pooled, and 25% of the entries will be selected to be winners, with a maximum of 25.</li>
<li>Each person can only wi... | 31,409 |
<p>The likelihood ratio (a.k.a. deviance) $G^2$ statistic and lack-of-fit (or goodness-of-fit) test is fairly straightforward to obtain for a logistic regression model (fit using the <code>glm(..., family = binomial)</code> function) in R. However, it can be easy to have some cell counts end up low enough that the test... | 70,458 |
<p>There was a concern raised by reviewers of a manuscript of mine over the proper execution of a Pearson's correlation. In brief, this was undertaken in order to determine the relationship between the extent of wheel running (y axis) and ethanol intake (x axis) across three, separate 10 day periods in 7 animals. </p>
... | 70,459 |
<p>What I'm essentially trying to do is a temporal external validation of a Cox Proportional Hazards model and also a logistic regression model on the newest year of a dataset that was not included during the development of these models. What I'd like to do is apply these models to the validation dataset and then obta... | 24,322 |
<p>I am trying to implement Linear Discriminant Analysis. I have 10 classes and each class has 3 observations at various instances: </p>
<pre><code>class 1 = {{a1,a2,a3}
{b1,b2,b3}
{c1,c2,c3}}
</code></pre>
<p><code>a,b,c</code> are 3 observations found at various instances <code>a1,a2,a3</code>. ... | 70,460 |
<p>This question is related to <a href="http://stats.stackexchange.com/questions/3842/how-to-create-a-barplot-diagram-where-bars-are-side-by-side-in-r">my previous question</a>. I would like to put values over bars in barplot. I am beginner in plotting in R.</p> | 31,415 |
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