question stringlengths 37 38.8k | group_id int64 0 74.5k |
|---|---|
<p>My objective is to implement a topic model for a large number of documents (20M or 30M). Let us assume that the number of topics is fixed at 50.</p>
<p>I think implementing an LDA for the above problem would not be difficult. However, I have yet to find an answer for an NMF model. I have read that it is NOT easy to... | 73,901 |
<p>I wonder if someone can explain what is the main difference between omega and alpha reliabilities?</p>
<p>I understand an omega reliability is based on hierarchical factor model as shown in the following picture, and alpha uses average inter-item correlations.</p>
<p><img src="http://i.stack.imgur.com/QH4Mf.png" a... | 73,902 |
<p>Note that there are some distributions that can be derived from the others (continuous as well as discrete).</p>
<p>For example student and chi-square distribution are derived from normal distribution and binomial distribution can be derived from Bernoulli distribution.</p>
<p>Of course, the term "derived" can be ... | 98 |
<p><strong>Modified question to better explain the context of my problem:</strong></p>
<p>I am studying young stars. When a star is born, it is surrounded by a disk of dust called "protoplanetary disk". Planets form in these disks, so understanding how they evolve gives information on plaent formation. Current theorie... | 36,447 |
<p>Note that this is a simplified example:</p>
<p>I have some time series that I made stationary by differencing twice. Then I ran <code>arima</code> on it, and set d = 0 to prevent additional differencing (I'm aware that <code>auto.arima</code> could detect the order of integration, but I'm hard-coding this myself fo... | 19,043 |
<p>I am looking at streaming data (i.e. online model), and looking for a specific discrete event. I want to stochastically model the time until this even happens, or if easier, say, model the probability that it happens within the next 30 seconds. What is a simple, practical way to tackle this problem? What kind of tec... | 73,903 |
<p>If the inflation indices was reset to 100 in the the 3rd quarter, what would be the fourth quarter inflation index for food. I have no idea how to do this . Below is the graph:</p>
<p><img src="http://i.stack.imgur.com/geO3v.png" alt="enter image description here"></p> | 73,904 |
<p><strong>I have applied the lm() to a data set. The independent variables are categorical.
First, I use lm() with intercept and I got the next results:</strong></p>
<pre><code>> model <- lm(y ~ factor(x))
> summary(model)
Call:
lm(formula = y ~ factor(x))
Residuals:
Min 1Q Median 3Q Ma... | 73,905 |
<p>I am working on a self-study question where </p>
<blockquote>
<p>A study indicates that the typical American woman spends USD 340 per year for personal care products. The distribution of the amount follows a right-skewed distribution with a standard deviation of USD 80 per year. If a random sample of 100 women is... | 73,906 |
<p>I want to use VIF to check the multicollinearity between some ordinal variables and continuous variables. When I put one variable as dependent and the other as independent, the regression gives one VIF value, and when I exchange these two, then the VIF is different. And once the VIF value more than 3, and the other ... | 36,454 |
<p>G. Monette and J. Fox provide in <a href="http://www.r-project.org/conferences/useR-2009/slides/Monette+Fox.pdf" rel="nofollow">these slides</a> a framework for the Type II Analysis of Variance/Deviance tests in terms of <em>conditional hypothesis</em>. My questions are:</p>
<ul>
<li><p>In this frequentist approach... | 6,873 |
<p>I have to calculate half life of an advertisement using Kalman filter in R. The paper 'Estimating the Half-life of Advertisements' (<a href="http://link.springer.com/article/10.1023%2FA%3A1008158119567" rel="nofollow">Naik, 1999</a><sup>[1]</sup>) provides the base but am unable to understand how exactly the estimat... | 73,907 |
<p>In relation to web usage mining from a log file, can you cluster data without performing User and/or Session identification? </p>
<p>I mean,let's say I have these entries:</p>
<blockquote>
<p>123.234.324.122 [timestamp] "GET /cars/sport/porsche.jpg" 200 23432 "http://topgear.com/cars" "Mozilladsfsd" </p>
<... | 45,351 |
<p>I want to determine the significance of a particular variable, among many confounders. If I fit a model on the training set and observe a small p value, should I discard the model because it extrapolates poorly on the test set (negative $R^2$ value), or should I keep it since I wasn't interested in predictions anywa... | 73,908 |
<p>I'm doing my PhD in geomechanics. I thought we use a Poisson-Weibull distribution (for the variability of a parameter at the rock), but reading more about the subject I think maybe is a Poisson-Weibull process and I don't know the difference (sorry I'm just a stupid engineer). To complete the problem I'm not too kno... | 36,456 |
<p>I'm given two random sample datasets of sample size n=20, where the first dataset represents the weights of random boys, and second group represents weights of random girls. I need to find the significance level of saying that boys on average weight more than girls.<br>
To solve this problem I'm assuming that the nu... | 73,909 |
<p>I have a data set of repeated observations and I am trying to determine if any of the observations are outliers. The research I've done has only shown methods that would determine if one value (maximum, minimum, or one questioned value) is an outlier, or if both the highest and lowest value are outliers. What I woul... | 73,910 |
<p>I've just come across a statement in </p>
<p>Good, P. I.: Resampling methods. Springer, 2001 </p>
<p>and wondered if someone could explain it to me.<br>
If you want to construct a 95% confidence interval for, let's say the mean of a normal distribution then the bounds would be $\bar{X}\pm 1.96s/\sqrt{n}$ with $\... | 73,911 |
<p>I have annual data that seem to have a bimodal density function. My explaination is that there is a distinction between wet and dry years.
For my work I would like to use an ar(1)-model for this. When I simulate from a fitted ar(1)-model with normally distributed innovations I of course get normally distributed dat... | 36,457 |
<p>According to the WinBUGS manual the gamma distribution is defined by:</p>
<p><code>dgamma(r,mu)</code></p>
<p>However, what is <code>r</code>? Is it the shape, scale or rate parameter? I'm pretty new to statistics and googling didn't really help. Above that in most explanations I've found <code>r</code>is usually ... | 73,912 |
<p>For Univariate Linear Regression I can calculate the parameters (And most everything else) from simple sum of squares. Is there a corresponding method for Logistic Regression?
Any pointers to code (in any language) would be helpful.</p>
<p>(Yes there are many solvers, but I want to implement as a simple Map-Reduce ... | 73,913 |
<p>I am trying to cluster data. Each point in this dataset is connected to some other points. I want to define clusters "depending on how much the points are connected to each other".
After some research, I read about k-core clustering (and saw it has applications in social networking for instance). I think this is the... | 36,458 |
<p>Let $x[n]$ be some time series in 1D or $x[m,n]$ in 2D, of length $N$ (resp. $N^2$) How can I assess whether it is <em>stationary</em>? At least in the weak sense. I can check whether the <em>stdev</em> remains constant, but this is only a necessary condition.</p> | 36,459 |
<p>I am trying to apply a simple Naive Bayes or SVM (libSVM) algorithms to a large data set, which I've constructed as an .arff file.</p>
<p>The number of features in my set is ~180k and there are ~6k examples. Also there are 8 classification classes. The data is of size ~3.2GB.</p>
<p>I am working with Weka's Java A... | 31,626 |
<p>I have data of a continuous random variable within the range [-1,1], which sometimes is concentrated around 0, while other times is concentrated toward -1 and 1, while zero is relatively underpopulated. </p>
<p>What measure can I use for both these cases to measure the divergence from a uniform distribution?</p>
<... | 73,914 |
<p>Here's <a href="http://stats.stackexchange.com/questions/125/what-is-the-best-introductory-bayesian-statistics-textbook">a link</a> to a good question regarding Textbooks on Bayesian statistics from some time ago.</p>
<p>People suggested John Kruschke's "Doing Bayesian Data Analysis: A Tutorial Introduction with R ... | 36,463 |
<p>I am looking for a (commonly used) probability density function, which would look like a normal distribution flipped upside down. It would look like a uniform distribution with a dent in the middle.</p>
<p>Just to be clear, I am dealing with a continuous random variable within some range, say <code>[-1,1]</code>.</... | 1,028 |
<p>In the context of REML estimation there is the result (ignoring some constants) that (my interest is in the matrix algebra so some notation is suppressed):</p>
<p>$l(\mathbf V_0)=\log |\mathbf V_0| + \text{tr}(\mathbf V_0^{-1}\mathbf S) \tag{1}$</p>
<p>Where both $\mathbf V_0$ and $\mathbf S$ are symmetric and inv... | 73,915 |
<p>Can the standard deviation be calculated for the harmonic mean? I understand that the standard deviation can be calculated for arithmetic mean, but if you have harmonic mean, how do you calculate the standard deviation or CV?</p> | 73,916 |
<p>I have a classification problem with two classes working on nominal data. I want to apply <a href="http://www.jair.org/media/953/live-953-2037-jair.pdf" rel="nofollow">SMOTE-N</a> to deal with imbalanced data. However, it is not clear to me how to use SMOTE-N for generating N synthetic data for each feature vector i... | 36,467 |
<p>I have got a set $\{Y_t\}$ of observations consisting of two subsets $\{Y_{t,1}\}$ and $\{Y_{t,2}\} \subset \{Y_t\}$ with $\{Y_{t,1}\} \sim \mathcal{N}(\mu_1,\sigma^2)$ and $\{Y_{t,2}\} \sim \mathcal{N}(\mu_2,\sigma^2)$ i.e. <em>different means but the same variance</em> (resulting from a regime switching model).</p... | 73,917 |
<p>I built a classifier with 13 features ( no binary ones ) and normalized individually for each sample using scikit tool ( Normalizer().transform).</p>
<p>When I make predictions it predicts all training sets as positives and all test sets as negatives ( irrespective of fact whether it is positive or negative )</p>
... | 73,918 |
<p>Given a $n$-dimensional multivariate normal distribution $X=(x_i) \sim \mathcal{N}(\mu, \Sigma)$ with mean $\mu$ and covariance matrix $\Sigma$, what is the probability that $\forall j\in {1,\ldots,n}:x_1 \geq x_j$?</p> | 73,919 |
<p>I have to write code to implement regression using random forests (by default Weka provides random forests for classification). Is this possible to do? </p> | 73,920 |
<p>I was hoping someone could propose an argument explaining why the random variables $Y_1=X_2-X_1$ and $Y_2=X_1+X_2$, $X_i$ having the standard normal distribution, are statistically independent. The proof for that fact follows easily from the MGF technique, yet I find it extremely counter-intuitive.</p>
<p>I woul... | 36,470 |
<p><strong>CONTEXT:</strong>
I am modelling the relation between time (1 to 30) and a DV for a set of 60 participants. Each participant has their own time series.
For each participant I am examining the fit of 5 different theoretically plausible functions within a nonlinear regression framework.
One function has one p... | 36,471 |
<p>I am trying to do a multiple logistic regression for 2 similar groups. I have a few questions:</p>
<ol>
<li><p>In doing a univariate analysis, do I enter each independent variable, one at a time, first into the binary regression, before going on to do the multivariate analysis? Or is the significance values from Ch... | 19,045 |
<p>I have two autocorrelation functions measured from the same stationary process, but the two measurements were taken with different instruments that measure different lag times. I would like to combine these two autcorrelation functions together into one single curve that spans the entire lag time of both instrument... | 73,921 |
<p>I want to simulate data from the following model:</p>
<p>$\textbf{z}_k=\textbf{H}\textbf{x}_k+\textbf{v}_k$ $\textbf{v}_k \sim N(\textbf{0},\textbf{R})$</p>
<p>$\textbf{H}$ does not change over time<br>
$\textbf{x}$ is a vector of loadings<br>
$\textbf{R}$ is a diagonal of constants</p>
<p>$\textbf{x}_k=\textbf{... | 73,922 |
<p>In considering (for example) homicide rates reported annually for each country, it occurs to me that the U.S., being larger in population, might thereby be expected to have a rate closer to the worldwide mean.</p>
<p>However, I don't know how to evaluate that idea quantitatively. What kind of additional data (if an... | 73,923 |
<p>I'm doing a binary classification using SVM classfier, libsvm, where roughly 95% belongs to one class.</p>
<p>The parameters C and gamma are to be set before the actual training takes place.
I followed <a href="http://www.csie.ntu.edu.tw/~cjlin/libsvm/">the tutorial</a> but still can't get any good results.</p>
<... | 6,882 |
<p>I take vitamins in the morning, but one of them I only take a half tablet. </p>
<p>So, I have an initial container with 100 full tablets, and every morning I take out a random tablet. If it's a full tablet, I break it in half, put half back, and take half. If it's a half tablet, I just take it. Given that, how ... | 36,476 |
<p>In a predictive linear regression model, does it make sense to combine binary and continuous data within a single scale?<br>
Does it make statistical sense to convert binary data into a z score? </p>
<p>I am wondering whether I could create a scale using a combination of binary and continuous items that I could co... | 36,479 |
<p>I have gotten a student job in the management department of a chain of 50 grocery stores. The job includes gathering daily statistics on the economy of the stores.</p>
<p>Every day a <strong>per-store revenue statistic</strong> is made, comparing the revenue to matching day last year (sunday/sunday, monday/monday) ... | 73,924 |
<p>I am currently calculating reliability estimates for test-retest data.</p>
<p>My question is regarding the difference between standard error of measurement (SEM) versus minimum detectable change (MDC) when seeking to determine if there is a 'real' difference between two measurements.</p>
<p>Here is my thinking thu... | 73,925 |
<p>I need help in knowing which test to perform with this analysis. </p>
<p>I have two groups (lets say group A and B). A study was performed with initial rates of heart failures in group A and B (i.e, baseline rates) were measured. After 6 months of follow up the heart failure rates in group A and B (i.e, re measure... | 73,926 |
<p>This is a more general treatment of the issue posed by <a href="http://stats.stackexchange.com/questions/104875/question-about-standard-deviation-and-central-limit-theorem">this question</a>.
After deriving the asymptotic distribution of the sample variance, we can apply the Delta method to arrive at the correspond... | 73,927 |
<p>In my research I'm comparing the variance of a method and I would like to describe the overall variance between individuals and the variance of the replicates of these individuals. </p>
<p>Things like 'comparing the intra-individual variance and between-individual variance' seems to get people confused. I would lik... | 73,928 |
<p>If somebody can tell me what R commands I need to use for a repeated measures ANOVA, I'd really appreciate it. I have trouble with the random term. I've seen <code>random=id</code>, <code>random=id/(treatment*group)</code> and others. </p>
<p>Also can you please indicate to me what the formula for the Bonferroni ad... | 49,613 |
<p>Suppose $X$ and $Y$ are two random samples (not necessarily iid, but one can make this assumption) and that $Z=X+Y$.
If one computes the order statistics of $X$ and $Y$, what can be said about the relative order statistic of $Z$?</p>
<p>To be more clear, let $\tilde{X}_{0.99}$ and $\tilde{Y}_{0.99}$ be the 0.99th q... | 73,929 |
<p>I'm learning about boosting. I think I understand how adaptive boosting works for classification. I'm trying to get some intuition for regression boosting.</p>
<p>At each iteration, adaptive boosting forces the next weak learner to focus more on incorrectly classified points. Intuitively, I can see why that shou... | 36,488 |
<p>I am trying to analyse diagnostic plots of a spline object, I am using the package <strong>Fields</strong> from <strong>R</strong>.</p>
<p>I am lost with the GCV function plot, since I can't find any guidelines of what to look for when comparing different models. Besides the value/degrees of freedom of the GCV func... | 73,930 |
<p>I have a one dimensional List like this</p>
<pre><code>public class Zeit_und_Eigenschaft
{
[Feature]
public double Sekunden { get; set; }
}
//...
List<Zeit_und_Eigenschaft> lzue = new List<Zeit_und_Eigenschaft>();
//fill lzue
</code></pre>
<p>lzue can be</p>
<pre><code>lzue.Sekunden
1
2
3
4
8... | 49,453 |
<p>I am running a 2x2x5 mixed factorial ANCOVA, with one within-groups variable, and two between groups variable. I want to check for violation of homogeneity of regression slopes. My covatiate does not interact with my between groups variables. It does however interact with my within-groups variable. Is this still ... | 73,931 |
<p>Suppose we have a data set $X$. This data set consists of ordinal data (4 levels). To get estimates of the threshold coefficients and probit slope ($\beta_1, \dots, \beta_3$ and $\beta_4$ respectively), do most computational packages use maximum likelihood estimation? That is, given the data, MLE chooses the paramet... | 73,932 |
<p>In Chemical industrial, samples are often analyzed multiple times, e.g. 5 samples and each was analyzed 2 times with 10 data points in total. What would be the confidence interval for the mean estimated from these data? The degrees of freedom is somewhere from 4 to 10 depending on the correlation between repeats.<... | 36,495 |
<p>I have some data I'm studying where functional data analysis seems
like a promising approach. But having never tackled FDA
before, I'm having trouble wrapping my head around it.</p>
<p>For background, I have Ramsay and Silverman's "Functional Data
Analysis" and Ramsay, Hooker, and Graves "Functional Data Analysis
... | 37,510 |
<p>The question is from a typical example for E-M algorithm. </p>
<p>Let's say $(y_1,y_2,y_3)$ $\sim$ $\text{multinomial}(n;p_1,p_2,p_3)$, where $p_1+p_2+p_3=1$. </p>
<p>How can we derive the conditional distribution of $y_2$ given $y_2+y_3=n$?</p>
<p>The answer is $y_2|y_2+y_3 \sim \text{binomial}(n, p_2/(p_2+p_3)$... | 73,933 |
<p>I do not know why testing homogeneity of variance is so important. What are the examples that require homogeneity of variance?</p> | 36,497 |
<p>I am running a structural Panel vector autoregressive model on a panel of 13 countries over the period 1970-2012. I'm having problems in implementing the model. Does anyone have estimation programs (from Matlab, Eviews, RATS or any time series package tool) so that I can use them to estimate my model? Thanks in adva... | 21,562 |
<p>When analyzing data, using MLE or Bayesian methods, one needs to assume a distribution for the data. For continuous data the are a number of distributions that are often considered, for example, the normal distribution, the t-distribution, the log-normal, etc.</p>
<p><strong>When analyzing the distribution of the ... | 42,522 |
<p>I have a binary outcome (success \ failure). I have 20 subjects, half of them gave 2 samples, the others just one, so I have 30 data points.</p>
<p>All data points without any exceptions were success (1). So my point estimate of the success rate is clearly 100%. Now I want to calculate a CI for the success rate, ma... | 31,914 |
<p>I'm new to Stata and didn't find the answer in the help, navigating the menus, or online so far. I would just like to know how to access the quantile function of a distribution. For example in R, if I want to know the 0.95 point of the $\chi^2(1)$ distribution, I do:</p>
<pre><code>> qchisq(0.95,1)
[1] 3.841459
... | 48,119 |
<p>Let's say, we have simple "yes/no" question that we want to know answer to. And there are N people "voting" for correct answer. Every voter has a history - list of 1's and 0's, showing whether they were right or wrong about this kind of questions in the past. If we assume history as a binomial distribution, we can f... | 36,500 |
<p>the following problem came up recently while analyzing data. If the random variable X follows a normal distribution and Y follows a $\chi^2_n$ distribution (with n dof), how is $Z = X^2 + Y^2$ distributed?
Up to now I came up with the pdf of $Y^2$:
\begin{eqnarray}
\psi^2_n(x) &=& \frac{\partial F(\sqrt{x})}... | 73,934 |
<p>In hypothesis testing, one must decide between two probability distributions $P_1(x)$ and $P_2(x)$ on a finite set $X$, after observing $n$ i.i.d. samples $x_1,...,x_n$ drawn from the unknown distribution. Let $A_n\subseteq X^n$ denote the chosen acceptance region for $P_1$.
The error probabilities of type I and II... | 73,935 |
<p>Conceptually, what is the reason why the correlation between growth rates of A and B would be different from correlation between actual A and B? Under what circumstances would the growth rate correlation be higher? How about lower? How about equal? Thanks.</p> | 73,936 |
<p>I have produced a model using the <code>ctree</code> function in R, and want to know whether this tree is actually explaining my data well. </p>
<p>I am trying to explain the presence or absence of landscape disturbances using environmental factors. <code>rpart</code> gives an $R^2$ value, but since my data are not... | 36,504 |
<p>Based on the lack of responses to <a href="http://stats.stackexchange.com/questions/78593/centralization-measures-in-weighted-graphs">my previous network question</a>, perhaps this is not quite the place to ask this question, but I'll give it a try.</p>
<p>I am planning a series of studies that involve small groups... | 73,937 |
<p>Can data sparseness appear due to either high sample size or high dimension? How different are the situations in the two cases? Thanks!</p> | 73,938 |
<p>I have UMVUE
$$\tilde\theta = \frac{(n-1)(U-n)}{(U-1)(U-2)}$$ for $P(Y=2)=\theta(1-\theta)$
where $U=\sum_{i=1}^n Y_i$</p>
<p>$Y_i \sim \text{geometric} (\theta)$
I am using delta method to find the variance of $\tilde\theta$</p>
<p>So far, I have defined:
$$g(y)=\frac{(n-1)(y-n)}{(y-1)(y-2)}$$</p>
<p>$$g'(y) = ... | 73,939 |
<p>(I'm asking this question for a friend, honest...)</p>
<blockquote>
<p>Is there an easy way to convert from
an SPSS file to a SAS file, which
preserves the formats AND labels?
Saving as a POR file gets me the
labels (I think) but not the POR file.
I tried to save to a SAS7dat file but
it didn't work.... | 36,505 |
<p>I have animals, that could be virgin or mated (reproductive state is the fixed factor), which I've stimulated sequentially with 4 different doses of an odour (doses are the repeated measures, the same animal was blown with 4 increasing doses of the same odorant). Then, I measure the neuronal response (variable: numb... | 73,940 |
<p>Obviously events A and B are independent iff Pr$(A\cap B)$ = Pr$(A)$Pr$(B)$. Let's define a related quantity Q:</p>
<p>$Q\equiv\frac{\mathrm{Pr}(A\cap B)}{\mathrm{Pr}(A)\mathrm{Pr}(B)}$</p>
<p>So A and B are independent iff Q = 1 (assuming the denominator is nonzero). Does Q actually have a name though? I feel ... | 49,547 |
<p>As the title says, I'd like to calculate the percentage difference for two sets of points. For example, suppose I have $S_{1}=\{(1,x_{1}),(2,x_{2}),(3,x_{3})\}$ and $S_{2}=\{(1,y_{1}),(2,y_{2}),(3,y_{3})\}$. How can I know the difference in percentage between both sets of data. What is the correct way to do that? Is... | 73,941 |
<p>Alright, hopefully third time is the charm. I'm basically trying to build a predictive model with R and gbm. For various reasons, I can't explicitly state exactly what I'm doing. </p>
<p>Basically I have a response variable that averages around zero. It has high volatility, is right skewed, and has very high kurtos... | 31,217 |
<p>I read in <a href="http://www2.sas.com/proceedings/sugi30/203-30.pdf" rel="nofollow">this paper</a> (page 3) comparing pca to factor analysis that both methods need a number of observations about 5 times the number of variables. Why? and how would you reduce the number of variables if you have few observations only?... | 73,942 |
<p>I am trying to get upto speed in Bayesian Statistics. I have a little bit of stats background (STAT 101) but not too much - I think I can understand prior, posterior, and likelihood :D. </p>
<p>I don't want to read a Bayesian textbook just yet.
I'd prefer to read from a source (website preferred) that will ramp me ... | 73,943 |
<p>I have two tables (matrix) of same dimensions, one contains correlation coefficients and other with p values. I want to combine them into one table. For example let's say I have correlation coefficient between variable A1 and A2 of 0.75 in table 1 and p value of 0.045 in table 2. Now in my combined table 3, I want t... | 73,944 |
<p>I know this is a fairly specific <code>R</code> question, but I may be thinking about proportion variance explained, $R^2$, incorrectly. Here goes.</p>
<p>I'm trying to use the <code>R</code> package <code>randomForest</code>. I have some training data and testing data. When I fit a random forest model, the <code>r... | 73,945 |
<p>I found the following posts interesting and I was wondering if any of you guys know of good academic papers that describe methods/relationships of exogenous variables in VECM models. If so could you kindly point them out to me as I am very interested in learning. Thank you.</p>
<p><a href="http://stats.stackexchang... | 48,143 |
<p>I've got a particular MCMC algorithm which I would like to port to C/C++. Much of the expensive computation is in C already via Cython, but I want to have the whole sampler written in a compiled language so that I can just write wrappers for Python/R/Matlab/whatever.</p>
<p>After poking around I'm leaning towards C... | 61 |
<p>I have a set of samples in which I assume there are 2 definite subsets in it. I plotted their values in a histogram and found that there are two distinct modes as shown in the figure below.</p>
<p>My question is how do I differentiate two groups. i.e how do I choose a value that differentiates the two subsets? </p>... | 36,512 |
<p>I am currently trying to do the following in R:</p>
<p>I have thousands of <strong>measured spectra</strong> (x,y; see below). Each spectra has one or two peaks. Also I have sets of <strong>"training" spectra</strong> obtained in more controlled conditions and I would like to know which of my training spectra has t... | 73,946 |
<p>I am trying to understand standard error "clustering" and how to execute in R (it is trivial in Stata). In R I have been unsuccessful using either <code>plm</code> or writing my own function. I'll use the <code>diamonds</code> data from the <code>ggplot2</code> package.</p>
<p>I can do fixed effects with either dum... | 48,146 |
<p>I have a Poisson regression where I regress a counts variable (called $H(x)$) on one covariate (called $x$) and one factor (categorical) variable (called $s$), which can take one of three values recoded to integers 1 through 3. I am including an offset variable called $P(x)$ and an intercept called $B_0$. I am tryin... | 73,947 |
<p>I'm using R to calculate the median absolute deviation for a few distributions, but some of the values I'm calculating do not seem realistic at all. I have the following distribution:</p>
<pre><code>x <- [1] NA NA NA -0.003 -0.009 0.004 -0.001 -0.001 -0.003 0.001 -0.002 0.000 -0.003 0.000 0.0... | 114 |
<p>So, it seems to me that the weights function in lm gives observations more weight the larger the associated observation's 'weight' value, while the lme function in lme does precisely the opposite. This can be verified with a simple simulation. </p>
<pre><code>#make 3 vectors- c is used as an uninformative random ef... | 73,948 |
<p>I am working with an investigator planning a study to validate a device to measure blood pressure (BP). The investigator states a difference within +/- 5 mmHg, when the two devices are used by the same participant, as "similar". I obtained the following summary statistics (slightly modified) from a similar study w... | 73,949 |
<p>So I am given the following question</p>
<blockquote>
<p>Data set sample5.txt has a 20-dimensional input $x$ in $\mathbb{R}^{20}$ but we
suspect that many of these are actually irrelevant. Could you model
the function $y = f(x)$ while - at the same time - figuring which
dimensions contribute to the output?<... | 36,518 |
<p>So I realize this has been asked before: e.g. <a href="http://stats.stackexchange.com/questions/48425/what-are-the-use-cases-related-to-cluster-analysis-of-different-distance-metrics">What are the use cases related to cluster analysis of different distance metrics?</a> but I've found the answers somewhat contradicto... | 49,393 |
<p>In a representative sample of country population I have very few missing data, around 3%. But when I checked the missing data among communities, I found that one of them has almost 30% of data lost. That's consistent in all ages.</p>
<p>Should I try to impute the data, remove that community from the analysis, or ke... | 73,950 |
<p>I'm new here and have a question regarding ANOVA in R. </p>
<p>I have an ANOVA table like this from running <code>anova(model)</code> in R, where <code>model</code> is a multiple linear regression model built with the <code>lm</code> command:</p>
<pre><code>Analysis of Variance Table
Response: log(price)
... | 73,951 |
<p>I have an interesting question that I think has not been asked yet here.</p>
<p>I am building an AI that has as goal to predict how wrong a standard based-on-history model is. This is done based on Natural Language Processing(NLP), so from an external source (yes I have thousands of articles timed by the minute to ... | 28,680 |
<p><strong>Context:</strong> I'm reading up on sampling in <a href="http://cis.temple.edu/~latecki/Courses/RobotFall07/PapersFall07/andrieu03introduction.pdf" rel="nofollow">MCMC for Machine Learning</a>. On page 5, it mentions rejection sampling:</p>
<pre><code>repeat
sample xi ~ q(x) and u ~ U(0,1)
if uMq(xi) &l... | 36,531 |
<p>I asked a group of subjects to make a series of 12 binary choices regarding preferences. </p>
<p>Let's say for arguments sake, these were between ugly (<code>ug</code>), attractive (<code>att</code>), and neutral (<code>neut</code>) faces. Hence, we have 4 <code>ug</code> vs <code>att</code>, 4 <code>ug</code> vs <... | 36,534 |
<p>Assuming I have a data set with $d$ dimensions (e.g. $d=20$) so that each dimension is i.i.d. $X_i \sim U[0;1]$ (alternatively, each dimension $X_i \sim \mathcal N[0;1]$) and independent of each other.</p>
<p>Now I draw a random object from this dataset and take the $k=3\cdot d$ nearest neighbors and compute PCA on... | 73,952 |
<p>I know that widget X has a population of N_x. However, widget Y has an unknown population that I'd like to estimate. </p>
<p>Both widgets appear with a differential frequency over time as I sample them.</p>
<p>Time ... X counts .... Y counts<br>
1 .......... 120 ............... 2<br>
2 .......... 212 .......... | 48,181 |
<p>A new virus breaks out on a cruise ship. I want to test the hypothesis that males and females are equally likely to contract the virus.</p>
<p>I am going to test 100 men and 100 women. Presumably if I find 87 women infected and 89 men I cannot safely reject the null. If on the other hand I find 11 men are affected ... | 37,289 |
<p>We often average models together to create an aggregate prediction model. Some recent research suggests that simple model averages perform as well or better than model averages weighted by functions of information criterion scores. Weighted or simple, model averaging often (but not always) performs better than choos... | 37,290 |
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