question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>Suppose I have two dependent categorical attributes A, B. I have a dataframe X that lists probabilities (or expected counts) for all combinations of all categories of A and B. Let's assume two categories in each attribute, the dataframe could then look like this:</p>
<pre><code>X <- data.frame(A = c(1,1,2,2), B ... | 73,090 |
<p><a href="http://en.wikipedia.org/wiki/Blum_Blum_Shub" rel="nofollow">Wikipedia says</a> that Blum Blum Shub is a pseudorandom generator whose ith value can be computed directly for a given seed. Wikipedia also says that this generator is too slow to be practical for simulation applications.</p>
<p>Is there any sta... | 39,992 |
<p>What should I look for when putting together a computer specifically for runnig R and similar programs. A lot of CPU power and RAM are given, but what about such things as an SSD and can R run on the graphics card? (like OpenCL..)</p>
<p>Thanks in advance.</p> | 73,091 |
<p>So I'm trying to derive the covariance between $z_t$ and $z_{t-1}$ in the $AR(1)$ model:
$z_t =\phi z_{t-1} + a_t$. Can anyone give me some advice on where to start?</p> | 49,913 |
<p>The concentration of impurities in a semiconducter in the production of microprocessors for computer is a normally distributed random variable with mean 127 parts per million and standard deviation 22 parts per million. A semiconducter is acceptable only if its concentration of impurities is below 150 parts per mill... | 73,092 |
<p>Suppose I have a non-linear model, say probit/logit, how can I understand the significance of a coefficient as opposed to the significance of it's marginal effect? Say, I just need to know the <em>importance</em> of a variable, would the former suffice?</p> | 73,093 |
<p>What is the difference between knowledge based annotation and corpus based annotation in the context of training a Machine Learning algorithm?</p> | 73,094 |
<p>I am designing a study for my project. I wanted to test if music affects reading comprehension. This study will be a between group design. The independent variable is type of music and the dependent variable is the score on a reading comprehension task.</p>
<p>Half of participants will be randomly assigned to a roo... | 49,914 |
<p>I have to evaluate a test paper which contains both dichotomous and polytomous items. I am currently using R. But in R IRT models for scoring of dichotomous and polytomous items are different and I have not found any way of combining both type of items so how can I mix both dichotomous and polytomous items into one.... | 73,095 |
<p>I am trying to build a model for auto rejection of crowd-sourced task (eg: human name transcription of census data). My data set has 5 predictors, and dependent variable is either correct or incorrect. However, there are few issues I have had.</p>
<ol>
<li><p>Data set is unbalanced with ~5% (up to 10% sometimes) of... | 73,096 |
<p>Suppose there exists a simple linear equation, where the dependent variable y(time series; measurements available) depends on x1 and x2. If the parameter multiplier of x2 is time dependent and the multiplier of x1 is a deterministic variable. How to find the pdf of the parameter multiplier of x2. Given the time seri... | 73,097 |
<p>They are both regression methods for discrete dependent variables. </p>
<p>I have a discrete dependent variables like $\{A, B, C, D, E\}$, and $A$, $B$, $C$, $D$, $E$ can be cardinal data(10, 20, 30...) or non-cardinal data(like car, train, and ship).</p>
<p>Which model is proper for each case?</p> | 35,298 |
<p>I am attempting to estimate the following model in Stata (the only statistics package I'm familiar with):</p>
<p>$$
Y_{t}=\alpha_{t} + \beta_{t}X_{t}+\varepsilon_{t}
$$
where $X$ and $Y$ are series and $\alpha_{t}$ and $\beta_{t}$ are time-varying parameters defined in state equations:
$$
\alpha_{t}=\alpha_{t-1}+\... | 38,072 |
<p>My original model is:
$Y=\alpha(\delta*X_1^{-\rho}+(1-\delta)*X_2^{-\rho})^{-\eta/\rho}exp(e_t)$</p>
<p>Which I partially linearize to:
$ln(Y)=ln(\alpha)-(\eta/\rho)*ln(\delta*X_1^{-\rho}+(1-\delta)*X_2^{-\rho})+e_t$</p>
<p>I've used a nonlinear least squares algorithm to estimate the parameters.</p>
<p>Now, I am... | 73,098 |
<p>I had just conducted a test where the customer wants to see a 20% improvement in perforation length from a baseline perforator. The baseline perforator has not been tested in the customer's specific conditions in which he will eventually perforate in. </p>
<p>The customer plans to shoot 40,000 perforations in the... | 73,099 |
<p>I would like to generate pairs of random numbers with certain correlation. However, the usual approach of using a linear combination of two normal variables is not valid here, because a linear combination of uniform variables is not any more an uniformly distributed variable. I need the two variables to be uniform.<... | 73,100 |
<p>I believe I have quite a simple problem, but want clarification on whether it is the best method to use.</p>
<p>Say I have have insurance line, and the net income (£) from this business for 2011, 2012, 2013 is 1,000,000; 4,500,000; and 5,000,000 respectively.</p>
<p>Hence, the percentage increase from 11-12 is 350... | 35,303 |
<p>In order to verify the assumption of proportional hazards, I plotted the following:
$$\log(-\log(S(t))) = \log(\Lambda(t))$$</p>
<p>If the hazards are indeed proportional for two groups, these curves should be parallel with the vertical distance being the log hazard ratio (which is constant if the proportional haza... | 35,305 |
<p>I am writing an algorithm where, given a model, I compute likelihoods for a list of datasets and then need to normalize (to probability) each one of the likelihood. So something like [0.00043, 0.00004, 0.00321] might be converted to may be like [0.2, 0.03, 0.77]. </p>
<p>My problem is that the log likelihoods, I am... | 35,307 |
<p>I am analysing a diagnostic test (against a gold standard, using a 2x2 table). I want to calculate likelihood ratios (sensitivity / (1-specificity) etc) however I have several sets of data with 0 false positives therefore a specificity of 1....</p>
<p>I have come across other <a href="http://www.aaos.org/research/g... | 73,101 |
<p>I have skewness of -0.5 in the residuals which does not seem to be improve much after using logs/root.
Is this a major concern? Tests relating to homoskedasticity, multicollinearity, outliers all seem fine. Perhaps interpreting the regression using robust standard errors would help..</p> | 73,102 |
<p>I need a closed-form expression for the probability that 2 values drawn at random from a normal distribution are separated by at most T, as a function of T and the variance of the distribution. I can formulate the problem as an integration, but can't solve it. I'd be happy with a well-motivated approximation. I'd be... | 73,103 |
<p>A random sample of size <code>n = 40</code> is taken. Conduct a goodness of fit test to see whether this sample appears to have been selected from a normal distribution. The number of intervals for the sample data is equal to:</p>
<pre><code>4
5
8
10
20
</code></pre>
<p>How do you calculate thi... | 73,104 |
<p>For the following model:</p>
<p>$$T = A_0 + A_1M+ A_2M^2 + A_3\ln(P) + A_4\ln(P)^2+A_5M\ln(P)$$</p>
<p>where:</p>
<blockquote>
<p>$T$ = Dependent variable </p>
<p>$P$ = Independent variable </p>
<p>$M$ = Independent variable</p>
<p>$A_0 \dots A_5$ = Coefficients of the regression.</p>
</blockquot... | 35,312 |
<p><strong>Background:</strong> Although <a href="http://en.wikipedia.org/wiki/Correspondence_analysis" rel="nofollow">correspondence analysis</a> is used mainly for <a href="http://www.datavis.ca/courses/grcat/grc5.html#H2_82%3aExample%3a" rel="nofollow">visualizing similarities of categories of two or more nominal va... | 73,105 |
<p>Some adapative test systems (e.g. school assessment tools) use the 1pl IRT model, while others use the 2pl or the 3pl. When developing an adaptive IQ test, is there a rule of thumb about which model to choose in calibrating the item difficulty and test takers ability? </p>
<p>I can't find any research that gives s... | 35,315 |
<p>So I have data that has been quantized by an analogue to digital converter. (continuous data has been turned into discrete data and the values range from 0 to the saturation value , which is 127 in this case). </p>
<p>This particular instrument I used to gather the data is quite noisy, let's say there is added Gau... | 46,638 |
<p>In a paper by <a href="http://www.ncbi.nlm.nih.gov/pubmed/23628224" rel="nofollow">Faraklas et al</a>, the researchers create a Necrotizing Soft-Tissue Infection Mortality Risk Calculator. They use logistic regression to create a model with mortality from necrotizing soft-tissue infection as the main outcome and the... | 35,318 |
<p>This question is kind of a follow up of another question I had: <a href="http://stats.stackexchange.com/questions/73830/asymptotic-normal-distribution-via-the-central-limit-theorem">Asymptotic normal distribution via the central limit theorem</a></p>
<p>There I had to calculate the estimator for $p$ (meaning $p$ fo... | 73,106 |
<p>I would like to compare 2 different classifiers for a multiclass text classification problem that use large training datasets. I am doubting whether I should use ROC curves or learning curves to compare the 2 classifiers.</p>
<p>On one hand, learning curves are useful for deciding the size of the training dataset, ... | 73,107 |
<p>I am looking for a robust version of Hotelling's $T^2$ test for the mean of a vector. As data, I have a $m\ \times\ n$ matrix, $X$, each row an i.i.d. sample of an $n$-dimensional RV, $x$. The null hypothesis I wish to test is $E[x] = \mu$, where $\mu$ is a fixed $n$-dimensional vector. The classical Hotelling test... | 73,108 |
<p>I have a dataset that contains ~7,500 blood tests from ~2,500 individuals. I'm trying to find out if variability in the blood tests increases or decreases with the time between two tests. For example - I draw your blood for the baseline test, then immediately draw a second sample. Six months later, I draw another... | 73,109 |
<p>I am having some problems figuring out what distribution my data best fits into.</p>
<p>My data is from a 100 mm visual analogue scale, so data points range from 0 to 100.</p>
<p>Participants were asked to score an animal's 'lameness' using these scales. There were 4 animals, all with varying severity of lameness... | 73,110 |
<p>I'm using a genetic algorithm (GA) to estimate the minimum value of a likelihood function $L[x]$ which is too complicated to evaluate mathematically. This likelihood function quantifies the goodness of fit between a model (which depends on the $x$ parameter) and a set of $M$ observations $O=\{a_1, a_2, ..., a_M\}$.<... | 3,415 |
<p>I am trying to compare readings from an old flowmeter and a new digital flowmeter to find out if they are significantly different. With the new meter I did readings under different conditions eg. calibrated at 30 seconds, calibrated at 60 seconds, uncalibrated at 30 seconds and uncalibrated at 60 seconds. I want to ... | 73,111 |
<p>Just a simple question on parameter selection for SVMs. If I use a minimum finding algorithm to find the optimal parameters for a set of data, how do I "average" the parameters over a set of cross validation runs to come up with the best parameters for my test set run? When doing X-fold cross validation, I can see s... | 35,331 |
<p><em>(ignore the R code if needed, as my main question is language-independent)</em></p>
<p>If I want to look at the variability of a simple statistic (ex: mean), I know I can do it via theory like:</p>
<pre><code>x = rnorm(50)
# Estimate standard error from theory
summary(lm(x~1))
# same as...
sd(x) / sqrt(length... | 46,656 |
<p>I'm trying to solve this problem out loud. I'm not great at statistics but I try sometimes to understand where things are and where they're going.</p>
<p>I'm trying to figure out the best method to compare the two following datasets. The first is the actual observation and the second is of what my sensor determined... | 73,112 |
<p>I've been reading some materials on Spatial data analysis, and I've a good background in GLMs. Right now I'm looking to find an example in spatial generalized linear models, but so far I've not found any. I'm aware of some packages in R such as GeoR. etc. but couldn't find a concrete example that includes codes, dat... | 73,113 |
<p>Its an interview question..</p>
<p>Initially there are n white balls. Each day you are allowed to take a ball. If the ball in hand is white, replace it by red ball. If it is red in color, put that ball into bag without doing anything. The question is to find the probability to have k red balls after d days.Give the... | 73,114 |
<p>I'm trying to use an inverse hyperbolic sine transformation to reduce the effect of outliers in my target variable. Unfortunately, I don't appear to have access to the basic papers on it. I've found the formulation but am not sure how to estimate the theta parameter for it. Does anyone know?</p>
<p>Thanks</p> | 73,115 |
<p>Then I fit linear models to the <code>plot(n_clust, error)</code> aiming to identify the best combination of I'm trying to perform a k-means cluster on my data (matrix with 2000 cases and 10 variables). I don't know how many clusters should I choose. To solve this problem, I adopted a strategy in which different val... | 35,334 |
<p>I have created a linear model (which has multiple predictors) using the lm() function and I would like to interpret the "coefficients" that I get when I use the summary() function on the linear model. <br><br>Now I want to consider how the coefficients reflect on the predictors' influence in the model - am I right i... | 35,336 |
<p>I am working with an anaerobic treatment plant where I have got main 3 variables, gas production (l/d), flow rate (l/h) and COD influent (g/l). if I want to do multiple l.regression, is it necessary to standardize (gas ~ flow+ COD) the variables?</p> | 49,325 |
<p>I am doing multiple regression with Gas production (l/d) as response variable, and flow rate (l/h) and COD influent (g/l) as explanatory variables in R. I made two models. </p>
<pre><code>mod1 <- gas ~ flow + COD
r^2 = 0.64
f stat= 56.62(2,64) with 0.0000.... p value.
mod2 <- gas ~ flow*COD
r^2 = 0.81
f... | 35,338 |
<p>Let's say I'm using the <code>Sonar</code> data and I'd like to make a hold-out validation in R. I partitioned the data using the <code>createFolds</code> from <code>caret</code> package as <code>folds <- createFolds(mydata$Class, k=5)</code>.</p>
<p>I would like then to use exactly the fold <code>mydata[i]</cod... | 35,339 |
<p>I am trying to use the package ‘fitdistrplus’ in R to fit one non standard distribution to my data set. I am trying to copy the methods the package creators used in their tutorial for specifying a Gumbel distribution but unfortunately I am not able to do it. </p>
<p>(The package documentation can be found in this <... | 73,116 |
<p>I have two variables each of which have three levels (low, medium & high). I would like to be able to test whether there is a significant trend between the two variables i.e. as x goes up y goes up. The trend tests I've looked at all seem to have one variable with 2 levels and the other with n levels.</p>
<p>... | 44,987 |
<p>After removing 25% (21 observations) of the sample as a holdout, model selection on the original 75% of the a sample led to a six variable multiple linear regression with R2 of 54%.</p>
<p>A simple regression of the holdout values on their predictions under the fitted model led to an R2 of 8% and and adjusted R2 of... | 73,117 |
<p>I have a complete population consisting of 6587 individuals (genes) and for each individual I have a distance value. These distance values are not normally distributed.</p>
<p>I'm interested in determining if a sample of 348 individuals (which has a smaller mean distance value compared with the mean distance value ... | 73,118 |
<p>If I need to determine the value of a data point at each percentile of a distribution (such as lognormal, weibull, etc), can use its CDF and plug in %iles to get the value?
For e.g. finding the value at 95%ile by plugging in 0.95 in the CDF formula. Basically, I need to determine that if the distribution graph were ... | 45,886 |
<p>I am interested in learning more about testing for the bivariate probit model with an endogenous treatment regressor. I have figured some stuff out -- summary below, since I don't see much on this topic -- but other questions remain. </p>
<p>Here's the setup. Suppose I have a binary outcome $y_1$, which depends on ... | 73,119 |
<p>Here is what I have :</p>
<p>A scaled training set, with labels.</p>
<p>Segmented images, from which I extract new vectors to classify.</p>
<p>My classifier is a KNN which would have obviously been trained using my training set.</p>
<p>Now, I wonder how I should scale those new vectors I just got. Is this correc... | 73,120 |
<p>Suppose I need to run <code>ttest bhar12=0</code> and the output comes as:</p>
<pre><code>One-sample t test
------------------------------------------------------------------------------
Variable | Obs Mean Std. Err. Std. Dev. [95% Conf. Interval]
---------+----------------------------------------... | 47,269 |
<p>I am trying to fit a second order polynomial. I center and scale my predictors and fit the data using the <code>lm</code> function. I did <code>summary(fit)</code>. For 3 of my variables, I got NA in all columns including estimate, p-value etc.</p>
<p>So, I am using R</p>
<p>I used the function <code>lm</code> as ... | 73,121 |
<p>Does it make sense to look at a scatterplot of means versus standard deviations in terms of looking for outliers or changepoints? So the mean is on the x-axis and the standard deviation is on the y-axis. We would get a clusters of data indicating similar data (relatively same mean and standard deviation). Note that ... | 46,674 |
<p>Let's say I have a vector of q-values, which allow for handling multiple hypothesis testing by controlling the false discovery rate. Usually, these q-values will be generated from a distribution of p-values.</p>
<p>However, what if I don't have the original p-value distribution, only the vector of q-values? Is ther... | 73,122 |
<p>I have this daily time series of observed prices: $P_1,P_2,..., P_n$.</p>
<p>I want to works with returns: $ 0 , P_2-P_1,..., P_n - P_{n-1}$.</p>
<p>I have been told to "remove" the first term (P_1-P_0= P_1- ?) by setting it to 0. It appears that this 0 is very differents from others terms and not a good solutio... | 35,348 |
<p>I have a large regression problem with a lot of cases, but relatively few independent variables. One of them is a categorical factor with thousands of levels. Robust regression runs forever. In some cases the large number of dummy variables becomes too sparse to calculate with even "normal" lm. </p>
<p>What would u... | 35,350 |
<p>I try to understand and visualize myself covariance matrix. Supposing I have a matrix <code>A = [ 2 3 4; 5 5 6 ]</code>, how do I calculate its covariance matrix, and what is its practical meaning? (All I was able to understand by now is that on the diagonal of the covariance matrix, variances for particular variabl... | 73,123 |
<p>Consider $U_i \sim^{iid} Bernoulli(\pi)$. Also consider:</p>
<p>$$Y_i | U_i = 0 \sim exp(1/\gamma) \text{ and } Y_i | U_i = 1 \sim exp(1/2\gamma) $$</p>
<p>What are the method of moment estimators of $\pi \text{ and} \text{ }\gamma$ ?</p>
<p>Here is my solution:</p>
<p>$E(U_i) = \pi \Rightarrow \hat{\pi_{MOM}} =... | 73,124 |
<p>I am desperately looking for some statistical help with my data because I myself cannot transfer the theoretical stuff I lately read on residuals, chi square distributions, squared z-values ecetera to my problem. Therefore I would really appreciate somebody to help me on that:</p>
<p>I compared 2 distributions with... | 46,677 |
<p>I'm rolling a regular dodecahedron (12-side die) 1200 times. I need to find an interval, in which the total count of prime-number results will lie with the probability of 95%. I have to use the Central Limit Theorem (CLT).</p>
<p>I'm not sure, how to use the CLT, but I have developed some way, how it could work. I'... | 34,216 |
<p>I am studying the book "<a href="http://rads.stackoverflow.com/amzn/click/1461471370" rel="nofollow">An Introduction to Statistical Learning: with Applications in R</a>", on page 66</p>
<p>While the book explains how to calculate $\beta_0$ and $\beta_1$, it skips how the actual calculation happened and only display... | 73,125 |
<p>I am working on fitting a GEE model to a multinomial logistic outcome using the R package <code>geepack</code>. My understanding is that the package uses <code>glm</code> to fit the formula. However, from what I can see, <code>glm</code> doesn't have a family for a multinomial outcome, just binomial. How do you go a... | 73,126 |
<p>Hi i was wondering how to figure out the following</p>
<p>Suppose $y=x+e$ where e is an i.i.d error. Say $x \sim N(\mu,\sigma_1^2)$ and $e \sim N (0, \sigma_e^2)$ which means $y \sim N (\mu, \sigma_1^2+\sigma_e^2)$. I need to find the expected value of y, conditional on $y>\mu$. I know that the formula will be y... | 73,127 |
<p>Suppose that we have 2 sets of data $X = x_1, \dots, x_n$ and $Y = y_1, \dots, y_m$ and a test $T$ that tests the null hypothesis that these data come from a distribution <strong>with the same median</strong>. $T$ can be for example the Mann-Whitney U test or the Wilcoxon signed rank test (if we have paired data). I... | 35,353 |
<p>the question is quite general, but I am doing a research related to supervised machine learning to classify two set of characters into two categories.</p>
<p>in fact, I want to compute some measures of similarity between a train set and the test set based on the N-gram approach.</p>
<p>I am trying to find a resour... | 24,882 |
<p>I just got admitted to the MS program in statistics at Villanova University (top 1 regional university in the North of the U.S.) and at Temple University (a third tier national university). I was wondering if anyone can give me some guidance regarding which university I should choose. Villanova does not have PhD pro... | 73,128 |
<p>I'd like to estimate a 3 level model (years clustered in districts clustered in counties) on the Leyland data (Mortality in England and Wales, 1979-1992 An Introduction to Multilevel Modelling using <code>MlwiN</code>) using R.</p>
<p>I have 3 predictors (year79 (at level 1), year792 (at level 1), and family(at le... | 35,355 |
<p>I made this linear regression that shows how well estimated animal locations (longitude) predict actual animal locations. </p>
<pre><code>estimate <- c(-1.514276, -1.513683, -1.514253, -1.514207, -1.513557, -1.513634, -1.513870, -1.511210, -1.511552, -1.511772, -1.511580, -1.511802, -1.509500, -1.510037, -1.5102... | 35,356 |
<p>I've been reading about Item Response Theory during the past few weeks and I'd like to use it to examine how my scales are functioning. The response categories are ordinal. If I understood well, the Graded Response Model is particularly appealing because it is more flexible than other alternatives such as the Partia... | 35,360 |
<p>I'm trying to interpret some results here, and just want to make sure that my logic is sound.</p>
<p>I'm predicting a binary outcome with a categorical predictor (gene level coded as 0, 1, or 2 dependant on the number of risk alleles present). My hypothesis is that the gene's effect on the outcome is because of its... | 73,129 |
<p>When comparing variances, very often a F-test is used.</p>
<p>$$F=\frac{s_1^2}{s_2^2}$$</p>
<p>We then compare $F$ to an F-distribution. The assumption of this test is that the two samples (which variances are $s_1^2$ and $s_2^2$) are normally distributed.</p>
<p><strong>Can you please explain why (given that the... | 35,362 |
<p>I'm creating a scoring system for web pages based on their level of readability using <a href="http://en.wikipedia.org/wiki/LIX" rel="nofollow">LIX</a>. A selection of pages from a web site are crawled and given a score. </p>
<p>Besides average and median, what alternatives do I have in order to reflect the score f... | 73,130 |
<p>As a work assignment, I've been asked to determine the optimal SKU count for a product group. I've decided to tackle this Q using a simple linear regression with sales as my dependent variable and the # of SKUs and the # of SKUs squared as my independent variables. My data set is a cross section of store sales and S... | 35,364 |
<p>As shown below, I'm trying to subtract TMin1array from Tarray. Does anyone know why the resulting array is returning all 0's? Tarray and TMin1array are of type double.</p>
<p><img src="http://i.stack.imgur.com/AJkCF.png" alt="enter image description here"></p> | 73,131 |
<p>I am using LMM in lmer. To find the most optimal model, I compare models of three-level with two level using ANOVA function. If it turns out that no significant difference between these two, then I compare two-level model with one level model. My formulas are like this:</p>
<pre><code>lmer1 <- lmer(peak_Mid ~ (1... | 35,367 |
<p>Let $(\Omega,\mathcal B,P)$ be a probability space. I have two (related) questions. Assuming that $g:\mathbb{R}\to\mathbb{R}$ is Borel measurable, and understanding that</p>
<p>$$E(g(X)) = \int_{\Omega}g(X(\omega))dP(\omega),$$</p>
<p>how do I prove that these equalities hold for the two following circumstances?<... | 73,132 |
<p>When does one use the denominator $\sigma$ over the denominator $\sigma /\sqrt{n}$? Why are there two separate forms and why does one look exactly like the t-score? Do some authors just call both t and z scores z scores?</p> | 35,369 |
<p>A short question concerning the constructing of a 'missing-dummy', which I will consequently add to my logistic regression. This missing-dummy gives value '1' to the cases where data concerning a specific variable is missing and value '0' to the cases which have data.</p>
<p>I've used this command in SPSS, but in s... | 73,133 |
<p>Statistical model for <em>Complete Randomized design</em></p>
<p>$y_{ij} = \mu + \tau_i + \epsilon_{ij}$</p>
<p>where, $i$ denotes treatment and $j$ denotes observation.</p>
<p>$i=1,2,...,k\quad and \quad j=1,2,..., n_i$</p>
<p>$y_{ij}$ be a random variable that represents the response obtained on the $jth$
obse... | 73,134 |
<p>I have a collection (approximately 12,000) correlation values. Our correlation analysis does not allow for negative correlations (we correlate with sinusoidal waves, so instead of a negative correlation, we simply positively correlate with the opposite phase).</p>
<p>This produces a distribution of positive r value... | 73,135 |
<p>Suppose we have a test statistic designed for testing a null about two groups of samples.</p>
<p>If we apply permutation test to the groups of samples and the test statistic, will that change the null hypothesis? </p>
<p>What I heard of before is that permutation test is to test if the two groups of samples are c... | 73,136 |
<p>I am working on a multinomial logistic regression problem which involves features from the dependent variable. It might be better to describe the problem by using the example in <em>mlogit</em> <a href="http://cran.r-project.org/web/packages/mlogit/vignettes/mlogit.pdf" rel="nofollow">mlogit manual</a></p>
<p>Here ... | 28,311 |
<p>Given a <em>partial sample</em> of values from a set (known size), how to extrapolate the lowest/highest value in the <em>entire set?</em></p> | 73,137 |
<p>Hate asking such a general question, but I'm so unfamiliar with statistics in general that I don't know what to search or where to find the answer.</p>
<p>I'd like to learn how to manipulate errors. Like, if I had a function $f\left(x,y,z\right)$, and I knew $\sigma_x,\sigma_y,\sigma_z$, what the error of $\sigma_{... | 46,697 |
<p>Boosting algorithms, such as <a href="http://en.wikipedia.org/wiki/AdaBoost">AdaBoost</a>, combine multiple 'weak' classifiers to form a single stronger classifier. Although in theory boosting should be possible with any base classifier, in practice it seems that tree-based classifiers are the most common. </p>
<p>... | 73,138 |
<p>I'm going to preface this all by saying that I'm pretty pedestrian when it comes to large statistical analysis.</p>
<p>I have approximately 11K discrete events and a corresponding score. I also have approximately 500 binary attributes. Each event is positive for one to six attributes. How do I go about trying to fi... | 73,139 |
<p>Imagine I organized a race between 2 types of ants. Type A and B.
At the end of the race, I have the ranking, which looks something like :</p>
<pre><code>1 A1
2 A3
3 B5
4 A4
5 B2
...
</code></pre>
<p>Where, in A1, A is the ant type and "1" the ant ID. Ants do not interfere between each other during the race. </p>
... | 73,140 |
<p>I have some data that span several years: 2006-2010. I have run logistic regression to model the data. For the whole dataset, I get a 95% confidence interval for the <strong>odds ratio</strong> of a parameter of interest of </p>
<pre><code>(0.34 - 0.47 )
</code></pre>
<p>indicating a very significant effect. Howe... | 35,383 |
<p>Feel free to direct me to where an answer can be found, but I've banged my head against this for a while and turn to you good people:</p>
<p>Scenario:</p>
<p>I have a bunch of non-exclusive two-dimensional data (location data) for several thousand unique observations of independent subjects:</p>
<pre><code>Subjec... | 24,384 |
<p>I wonder between two performance metrics for classification models: accuracy and area under ROC curve (AUC), which one is to be preferred in which conditions? examples appreciated</p> | 35,384 |
<p>I posted this to the TraMineR user list and it was suggested that it would be appropriate to post it here as well.</p>
<p>Any suggestions as to how to determine the minimum dataset size and missingness characteristics to which TraMineR may be applied sensibly would be helpful. I looked for information in documentat... | 73,141 |
<p>I have a random sample $(X_1, X_2,...,X_n)$ and I have an estimator $\bar{X_n}=\sum_{i=1}^{n} X_i$</p>
<p>I need to compute the Fisher information of $\bar{X_n}$. The Fisher information is defined as $-E\left(\frac{d^2}{d\theta^2}logL\right)$, where $L$ is the likelihood function.</p>
<p>My question is: to compute... | 73,142 |
<p>I have a number of distance matrices that I want to associate their members with a probability distribution. Is there a method which can affiliate each distance matrix with a distribution?</p>
<p>EDIT:
Lets say I have a distance matrix like:</p>
<pre><code> A1 A2 A3 A4 ...
A1 X 1 3 2
A... | 73,143 |
<p>I have an experimental design with attitudes toward one positive and one negative stimulus nested within individuals. I also have a continuous predictor at the person level (a personality construct).<br>
My plan was now to build a multi-level model with valence as level-1 predictor, (centered) personality as level-2... | 35,387 |
<p>Does returning z-scores to a set mean and deviation result in a fair comparison? That is if I had 2 groups:</p>
<ul>
<li>group 1 mean = 76, stdev = 8</li>
<li>group 2 mean = 81, stdev = 11.</li>
</ul>
<p>Then to compare group 1 & 2 I return the groups scores using the z-scores against a set mean = 70 and stdev... | 73,144 |
<p>Age pyramid looks like this:
<img src="http://i.stack.imgur.com/GtBSK.png" alt="alt text"><br>
I would like to make something similar, namely a 2 barplots (not histograms) with same categories, rotated vertically and extending to both sides as in pyramid.<br>
Is it a simple way to do this in R?<br>
It would be also ... | 35,388 |
<p>I would just like someone to confirm my understanding or if I'm missing something.</p>
<p>The definition of a markov process says the next step depends on the current state only and no past states. So, let's say we had a state space of a,b,c,d and we go from a->b->c->d. That means that the transition to d could onl... | 49,390 |
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