question stringlengths 37 38.8k | group_id int64 0 74.5k |
|---|---|
<blockquote>
<p>The annual profit for your organisation last year was £1203,
per employee. The average for the sector was £1228 per employee.
You need to know if there is evidence that your organisation is not
as profitable, on average, as your competitors. The standard
deviation for the sector is £104 per em... | 71,430 |
<p>I had heard that there is a body of literature devoted to the following problem:</p>
<p>You have a dataset and you produced a good predictive model for it. Now you have a different dataset, derived from different instruments, or different data sources, but similar enough that you can hope to scale one to the other ... | 71,431 |
<p>I've got one independent variable and two dependent variables. As a concrete example, consider the independent variable to be <em>browser</em> (categorical, what Web browser a visitor to a Web site uses) and the dependent variables to be <em>visitors</em> (number of visitors) and <em>enrollers</em> (number of visito... | 37,863 |
<p>This question is in response to an answer given by @Greg Snow in regards to a <a href="http://stats.stackexchange.com/questions/35918/logistic-regression-the-standard-deviation-used-in-glmpower">question</a> I asked concerning power analysis with logistic regression and SAS Proc GLMPOWER.</p>
<p>If I am designing a... | 71,432 |
<p>Is there a generic answer as to how the log transform affects the Pearson correlation between two variables, i.e., is $\rho(\log(x),\log(y)) < \rho(x,y)$ always or the other way around and why?</p> | 71,433 |
<p>I noticed that when I have tables which the values are only 0 and 1, I get a kappa of 1 when the table is completely full of one, and when I have a table of zeros I get NaN as result using the irr package and the kappa fleiss function. </p>
<p>I would expect the kappa to be also equals to 1 when the table is full o... | 32,874 |
<p>I would like to simulate interval-censored data in a Cox model. In the R package <code>intcox</code> I found the following code:</p>
<pre><code>sim.weibull.intcox.rfc <-function(N=200, beta.0=0.1, beta.cov=c(0.5,-0.5,0.5,0.5),
alpha=0.75, p.cov=c(0.5,0.75), grid=10)
{
x.design... | 71,434 |
<p>I am looking to measure agreement between participants in choosing which member of a group is most like certain attributes. I want to calculate the expected agreement if they were to choose by chance.
e.g. assume we have 3 participants (P1, P2, P3) and they can choose from a list of 3 people (A,B,C) to associate wit... | 71,435 |
<p>I've thought quite a lot on large sample size inference where the strong law of large numbers is easily validated. In my case however, I'm trying to infer the sign and magnitude of an outcome where the noise-to-signal is quite large in comparison to my available sample size.</p>
<p><b>How do I properly test for goo... | 71,436 |
<p>I have a bunch of documents where some of the documents are a copy of other documents with their text jumbled up and some of the words replaced by their synonyms. Mentioned below is one such example of a sentence:</p>
<blockquote>
<p><strong><em>Article 1 (original)</em></strong> : I caught up with John Snow in t... | 71,437 |
<p>Consider two independent and identically distributed random vectors of dimensionality $N$, $\mathbf{x}$ and $\mathbf{y}$, where their elements are iid generated from a Gaussian with zero mean and variance equal to $\sigma^2$; i.e., $\mathbf{x} , \mathbf{y} \sim \mathcal{N}(0, \sigma^2)$. </p>
<p>What is the probabi... | 38,244 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://stats.stackexchange.com/questions/6619/probability-of-getting-between">Probability of getting between</a> </p>
</blockquote>
<p>What is the probability that at least 24 of the next 50 people like to swim when the true probability of people... | 49,874 |
<p>Suppose that we have a linear model $y_i = \beta_0 + \beta_1 x_i + \epsilon_i$ that meets all the standard regression (Gauss-Markov) assumptions. We are interested in $\theta = 1/\beta_1$. </p>
<p><strong>Question 1:</strong> What assumptions are necessary for the distribution of $\hat{\theta}$ to be well defined? ... | 71,438 |
<p>Is there a good heuristic for what fraction of the data to use when training a random forest with bagging? I imagine this fraction should depend on the number of trees in the forest, like 2/3 1/<em>N</em><sub>trees</sub>, where <em>N</em><sub>trees</sub> is the number of decision trees in the forest.
Please point me... | 10,074 |
<p>I understand that a stationary time series is one whose mean and variance is constant over time. Can someone please explain why we have to make sure our data set is stationary before we can run different ARIMA or ARM models on it? Does this also apply to normal regression models where autocorrelation and/or time is ... | 43,757 |
<p>I'm dealing with a homework.</p>
<p>We were given a software, with inputs, that we should measure and then verify that the time complexity is O(n^3).</p>
<p>I measured the software, picked best times from each batch (since that's the least affected one), and ended up with this:</p>
<pre><code>304 70000
574 48... | 71,439 |
<p>I have two groups of samples with a proportion of mutations in each sample being a particular type (the proportions are represented as a fraction of 1). How to I check if that type of mutation is significantly likelier to happen in one group over the other? </p> | 71,440 |
<p>I am building a multivariate Gaussian Process model that predicts output $X_i$ and $Y_i$ jointly from input location $z_i$. At the end of it all I want to be able to plot my best estimate of $X_i$ against $Y_i$ where I know that </p>
<p>$$\begin{pmatrix}
X_i\\
Y_i
\end{pmatrix} \sim N_2
\begin{pmatrix}
\begin{pmat... | 32,882 |
<p>Suppose $\theta$ is the probability that a <a href="http://en.wikipedia.org/wiki/Bernoulli_random_variable" rel="nofollow">Bernoulli random variable</a> is one (therefore $1-\theta$ is the probability that it's zero). I have a sequence of $n$ of these i.i.d. Bernoulli random variables, $m$ out of which are ones. I... | 71,441 |
<p>I'm reading Bishop on EM algorithm for GMM and the relationship between GMM and k-means. </p>
<p>In this book it says that k-means is a hard assign version of GMM. I'm wondering does that imply that if the data I'm trying to cluster are not Gaussian, I can't use k-means (or at least it's not suitable to use)? For e... | 71,442 |
<p>I have some p-values that I want to convert to q-values. The issue I am running into is that the qvalues being generated by storey's qvalue package are all in a very tight range (i.e. .25-.35).</p>
<p>I am not sure what this means. I am working with a ridiculously small dataset, given the number of hypotheses, co... | 71,443 |
<h3>Note: I <em>am</em> aware of <a href="http://stats.stackexchange.com/questions/31867/bayesian-vs-frequentist-interpretations-of-probability">philosophical</a> differences between Bayesian and frequentist statistics.</h3>
<p>For example "what is the probability that the coin on the table is heads" doesn't make sens... | 49,737 |
<p>I'm using the Matlab Neural Network toolbox for a regression problem (twelve inputs, one target). My target has a high dynamic range and is strongly non-gaussian. So far I've solved this by a log-transformation, but as an alternative I'm exploring if a different error function than the standard mean square error wou... | 38,427 |
<p>I have a class with a set of descriptive statistic functions (mean, median, kurtosis, etc...).</p>
<p>Now I need to include weight (array) into my equations. My first thought was to just create a weighted version of the functions where the additional weight array is passed.</p>
<p>However, I was wondering if there... | 43,777 |
<p>I know what you're thinking, this is a duplicate of "<a href="http://stats.stackexchange.com/questions/1576/what-are-the-differences-between-factor-analysis-and-principal-component-analysis">What are the differences between Factor Analysis and Principal Component Analysis</a>", but it isn't really.</p>
<p>That othe... | 43,778 |
<p>If I use the fast99 method (from the sensitivity package) with qnorm, it generates parameter sets with -Inf and Inf in, which are not much use for then running models:</p>
<pre><code>> f <-fast99(model=NULL,factors=c("a","b"),n=100,M=4,q=c("qunif","qnorm"),q.arg=list(a=list(min=0,max=1),b=list(mean=0,sd=5)))
... | 43,779 |
<p>I have a sample of animals and a categorical variable of $L$ behaviors $i=1,...L$. I computed the proportions of this sample corresponding to each behavior category $p_{i}$, $\sum p_{i}=1$. </p>
<ol>
<li>Can I use a common method of confidence interval for a proportion (e.g. Clopper-Pearson) to compute the CI for e... | 71,444 |
<p>I am using Mutual Information on a data set with some outliers.</p>
<p>The univariate variables don't have a known distribution, so I cannot remove them automatically with any neat method, like Grubbs or Studentized tests. Hence, As I must work with a dirty data set, the methods that I apply must be robust against ... | 71,445 |
<p>I am dealing with sentiment results of web articles. Sentiment is represented with two int values, +ve and -ve.</p>
<p>For given article "xyz" I am getting different sentiments while testing at different time period. Each result has +Ve and -ve value and value are close to each other. I represent them using 2-D Gra... | 10,242 |
<p>Even after reading the original paper on LASSO, I am still confused as to how to apply LASSO for variable selection when the response variable <em>y</em> is a matrix (and not a vector) of <em>n</em> dependent variables with <em>t</em> observations each. </p>
<p>As an example, the response variable <em>y</em> is mo... | 71,446 |
<p>I am running multiple imputation for a set of variables including clinical data. I am wondering if I can use (or should use) outcome variable (follow-up is 99%) to predict missing clinical data. There is about 12 % of non complete cases due to mostly one variable. I intend to use Amelia package (R)?</p>
<p>I would ... | 32,888 |
<p>So I'm looking to compare different combinations of features and classifiers. But I'm getting a lot of combinations that achieve 100% cross validation accuracy. I'm trying to figure out how I would compare the usefulness of each combination.</p>
<p>For example I can both train an SVM using Features 1, 10, 15 to get... | 71,447 |
<p>I have a very basic model development question. </p>
<p>The objective is to develop a predictive model. Let's say I have a dataset with 50,000 observations.
Take a random split of this dataset into train (N=25000) and validation (N=25000) datasets (we know some folks prefer a test dataset but assume we are not goin... | 71,448 |
<p>I need to predict if a bus will stop at a particular scheduled route stop. I have GPS coordinates, I can check door signals, the stops have radii, and I also have historical data about if the bus skipped a stop or not. I want to use this information to train a model predicting whether a bus will stop at a particular... | 71,449 |
<p>I have carried out a linear regression. The plot below shows the distribution of the response variable:</p>
<p><img src="http://i.stack.imgur.com/4RtjY.jpg" alt="enter image description here"></p>
<p>I believe the response variable is beta distributed, therefore virtually the exact opposite of normally distributed... | 71,450 |
<p><img src="http://i.stack.imgur.com/QcPfC.jpg" alt="enter image description here"></p>
<p>I am not sure how I can solve this optimization problem. I have a (MATLAB) code which can solve this but only for very low dimensions, that is, low values of $n$ (around $n = 4$ or $5$), once $n$ exceeds $10$, the code suffers ... | 32,890 |
<p>I am trying to use the R pROC package to estimate the confidence interval for the area under the curve (AUC). I am running into a memory limitation. My R script looks like the following:</p>
<pre><code>library(pROC)
data <- read.csv("data.csv",header=TRUE)
rocobj <- roc(data$observed, data$predicted)
ci(rocob... | 30,627 |
<p>I currently have <a href="http://math.stackexchange.com/questions/74675/showing-that-normalized-redundancy-is-nonreliant-on-the-properties-of-bijection">an output function</a> that roughly follows a <a href="https://en.wikipedia.org/wiki/Chi-squared_distribution" rel="nofollow">$\chi^2$ distribution</a> for random d... | 71,451 |
<p>I have 4.4 million observations, 160 binary features, and a binary response. Using rpart on Windows (64-bit, with the 64-bit R v2.13.0 build), I run out of memory on a machine with 64GB RAM. My memory limit seems reasonable:</p>
<pre><code>> memory.limit()
[1] 61440
</code></pre>
<p>But on running rpart, I stil... | 71,452 |
<pre><code>10/16/2011 9:33:46 AM
10/16/2011 9:54:48 AM
</code></pre>
<p>The above are a few rows from my G$time column. I wanted to convert them to readable form when I graphed Y over Time, so I tried</p>
<pre><code>Time<-strptime(G$Time,format="%D %H:$M:%S %r")
</code></pre>
<p>and then</p>
<pre><code>Time&l... | 43,786 |
<p>I'm using a beta binomial updating model for a piece of code that I am writing. The software is real time updating - meaning that data is continually being gathered and after N data points are gathered, the bayesian model is updated using the N data points. </p>
<p>Under this logic, I am using the posterior output ... | 43,788 |
<p>A given user can interact in multiple ways with a website. Let's simplify a bit and say say a user can:</p>
<ul>
<li>Post a message</li>
<li>Comment a message</li>
<li>"like" something on the website via Facebook</li>
</ul>
<p><em>(after that we could add, following the site on twitter, buying something on the sit... | 71,453 |
<p>I'm collecting online recipes in order to calculate average ingredient proportions for, say crepes or pastry. Most volume based units of measure in english recipes (cups, tablespoons, teaspoons) differ from country to country and sometimes differ within the same country depending on whether traditional, metric or go... | 32,897 |
<p>I am looking for improving a certain process. Several variables are measured about the performance of this process. My endeavour is to identify some critical variables so that I can run DOE to optimize this process. </p>
<p>I ran a PCA. I find that too many variables are entering each PC. What can be done?</p> | 71,454 |
<p>I have some data like this:</p>
<pre><code>id pop var
1 593 51
2 592 31
3 346 20
4 1214 70
5 1063 66
6 1370 71
</code></pre>
<p>each <code>id</code> represents a school. There are around 1847 of them, of which 1833 are unique . <code>pop</code> is the number of pupils in the s... | 43,760 |
<p>I have been wondering about this for a while. When I have mutually exclusive dummies in the same regression, are their coefficients independent?</p>
<p>For example, suppose I have the following: </p>
<p>$y_{i}=\mathbf{\mathbf{\alpha'}}\mathbf{x_{i}}+\beta_{0-5}I\left\{ z_{i}\in\left[0,5\right]\right\} +\beta_{6-10... | 32,898 |
<p>I am working with a bunch of multinomial models, and presenting the tables with all the coefficients is getting to be quite tedious, do you guys know of any ressources that show how to present such models graphically, so all the tables could be excluded, or put in an appendix?</p> | 71,455 |
<p>What is the motivation for demeaning the data when doing PCA. I've been told to do it, but I've never heard a good and/or intuitive reason for it. Is this a case where doing it just makes the math easier, or is it more like: if you don't do it, you'll get the wrong answer.</p>
<p>This is something I've been wonderi... | 49,463 |
<p>I have been trying to fit a spatio-temporal variogram based on Cressie's WLS criteria. </p>
<p>\begin{equation}
W (\theta) \equiv \sum_{l=1}^{L} \sum_{u=0}^{U} |N (\mathbf{h}(l);\, u)| \displaystyle \left \{ \frac {\hat{\gamma} (\mathbf{h}(l);u)}{\gamma (\mathbf{h}(l);u| \mathbf{\theta} )} -1 \right \} ^2
\end{equ... | 71,456 |
<p>I was reading the slides from the following</p>
<p><a href="http://www.slideshare.net/kunegis/searching-microblogs-coping-with-sparsity-and-document-quality" rel="nofollow">http://www.slideshare.net/kunegis/searching-microblogs-coping-with-sparsity-and-document-quality</a></p>
<p>In slide 7, the author proposed ju... | 71,457 |
<p>I work at a software company, and we are trying to build a statistical model to predict the defect density (the number of defects that exist in a certain software release that is delivered to a customer divided by the number of person months that it took to develop the software release). </p>
<p>We have 15 independ... | 32,900 |
<p>Currently I only know about the imbalanced in the structure of data set (e.g. too many positive samples, few negative samples..). But how about imbalanced in the value of features in each samples? For example, I have a sample with label A, that has 4 features, value of each feature is:</p>
<ul>
<li>A 1:-2000 2:50 3... | 32,901 |
<p>I have some power-law data sets coming from an Ecology study. Some of them seem to be best modeled using linear regression after log-transformation of the data, but other data sets seem to be best modeled using nonlinear regression. A third group of data sets could be modeled using an average model. </p>
<p>For eve... | 32,902 |
<p>This question's context is time series forecasting using regression, with multivariate training data. With a regularization method like LARS w/ LASSO, elastic net, or ridge, we need to decide on the model complexity or regularization parameters. For example, the ridge $\lambda$ penalty or the number of steps to go a... | 48,315 |
<p>We have two huge correlation matrices at different experimental conditions. If we want to identify the significant differences between these matrices , what would be the ideal method. I have implemented PCA for dimentionality reduction for the two matrices, and compared both row by row. Will it give some information... | 32,904 |
<p>Consider the case that I need to do cross-validation for SVM to obtain a good estimate of the cost parameter $C$. I am not sure when should I divide the data into $K- $ folds. </p>
<p>To perform the cross-validation:</p>
<p>Step 1. Split the data into K folds (by random sampling these data points)</p>
<p>Step 2. ... | 71,458 |
<p>I'm trying to find out if a nominal variable <code>A</code> (2 values: <code>x</code> and <code>y</code>) and a numerical variable <code>B</code> (integer) are somehow related. E.g., does <code>A</code>=<code>x</code> mean that <code>B</code> will be lower than when <code>A</code>=<code>y</code>. I'm working with SP... | 71,459 |
<p>I have read that using R-squared for time series is not appropriate because in a time series context (I know that there are other contexts) R-squared is no longer unique. Why is this? I tried to look this up, but I did not find anything. Typically I do not place much value in R-squared (or Adjusted R-Squared) when I... | 71,460 |
<p>Does anyone know how to construct a confidence interval for predicting a new test value given a trained Relevance Vector Machine (<code>rvm</code>) and/or Gaussian Process Regression (<code>gausspr</code>) using the <a href="http://cran.r-project.org/web/packages/kernlab/index.html">kernlab</a> R package?</p>
<p>Mo... | 71,461 |
<p>My dataset consists of binary preferences ($0$ or $1$) given by users on items like this:</p>
<blockquote>
<p>User-ID | Item-ID | Preference</p>
</blockquote>
<p>If a user has not given a preference to an item, then it is not in the dataset. (In essence this means there are three possible values in a user-i... | 32,909 |
<p>Sometimes I need to get only the first row of a data set grouped by an identifier, as when retrieving age and gender when there are multiple observations per individual. What's a fast (or the fastest) way to do this in R? I used aggregate() below and suspect there are better ways. Before posting this question I sear... | 32,910 |
<p>I've been trying to figure out how to properly report a two way ANOVA with two between-subject variables and their interaction. Most references I found suggest to report it in the following way: <code>F(df between-subject, df within-subject)=f-value, p=p-value</code>, e.g. <a href="http://osil.psy.ua.edu/~Rosanna/PY... | 71,462 |
<p>I have some random numbers which are generated from Gaussian Distribution. But I don't know the mean, standard deviation of that distribution. How can I find them using random numbers?</p> | 952 |
<p>I’m trying to estimate the out-of sample forecast of an ARIMA model, I tried the code below, but it totally doesn’t work!</p>
<pre><code>for(i in 1:83) {
mod[i] <- arima(window(betahat[,1], start=1, end=109+i),order=c(1,0,0),include.mean=TRUE)
pre[i] <- predict(mod[i],12)
error[i] <- pre[i]$pred[... | 71,463 |
<p>The Breslow estimate is commonly used in the Cox proportional hazards model. However this paper by Deborah Burr</p>
<blockquote>
<p>Burr, D. (1994). <a href="http://www.jstor.org/pss/2533450" rel="nofollow">On Inconsistency of Breslow's Estimator as an
Estimator of the Hazard Rate in the Cox Model</a>. <em>Biom... | 71,464 |
<p>What is the semantic difference between Mean Squared Error (MSE) and Mean Squared Prediction Error (MSPE)?</p> | 71,465 |
<p>About crossed factorial design, two factors A and B are crossed, if every level of A can occur in every level of B. </p>
<p>A full factorial/crossed experiment is an experiment
whose experimental units take on all possible combinations of these levels across all such factors.</p>
<p>If I am correct about the above... | 32,913 |
<p>I understand that the output of, for example, <code>summary(lm(Fertility ~ . , data = swiss))</code> is a table of $\hat\beta$s, standard errors, t-statistics, and p-values for two-sided tests of the null hypothesis that each parameter is equal to 0.</p>
<p>But, what should I actually call this method of evaluating... | 10,401 |
<p><a href="http://www-01.ibm.com/software/analytics/spss/products/modeler/" rel="nofollow">SPSS Modeler</a> seems like a great tool for data mining (especially for prediction etc.) but it is extremely costly for individuals like me (around 20,000 euros excl. tax). There is also a <a href="http://www.youtube.com/watch?... | 43,812 |
<p>I have some overdispersed count data (mean=8.6, var=263.5) that I am hoping to model using either a negative binomial (NB) or quasipoisson GLM. A rootogram suggests that the Poisson distribution is a poor fit. </p>
<p>I compared three different models: Poisson, NB, and quasipoisson.</p>
<pre><code>fake = structure... | 32,917 |
<p>I'm working on a way to make efficient classification on sequential patterns mining algorithms. Looking in the state-of-the-art I found that there is two type of algorithm to address this problem : <code>discriminative</code> and <code>emerging</code>. </p>
<p>Can someone help me understand : </p>
<p>1- what is t... | 32,918 |
<p>I clustered data according to latitude and longitude.Use the kmeans++ for increasing the accuracy of kmeans. But still result does not change much.
Here is my db index graph for kmeans++
<img src="http://i.stack.imgur.com/2QD1Z.png" alt="For Kmeans++"></p>
<p>For kmeans</p>
<p><img src="http://i.stack.imgur.com/iN... | 71,466 |
<p>My work implies a lot of econometrics, and I had a good formation about it. Nevertheless, I am regularly faced with some semi or non parametric techniques (for instance I had to use quantile regressions, partial estimation, or nonparametric estimation of whole distribution estimations), and I had no courses about it... | 71,467 |
<p>I am doing comparisons on response rates across three sites. Following are the cell counts</p>
<pre><code> Frequency |
Percent |
Row Pct |
Col Pct | 0| 1| Total
... | 45,980 |
<p>How to get the distribution of Welch Statstic:
$ \sum_t w_t(y_t - \hat{y})^2 $
in journal article <a href="http://www.google.com/url?sa=t&rct=j&q=Welch%2C+B.+L.+%281951%29.+On+the+comparison+of+several+mean+values%3A+An+alternative+approach.+Biometrika%2C+38%2C+330-336.&source=web&cd=1&cad=rja&am... | 71,468 |
<p>I am new to the wonderland called Statistics. I studied a lot (finished Greene) about linear regression but I never got this clear in my head: if I am given data and asked to run a regression, what tests should I run to see whether data is appropriate to run a good regression? How do I know my data is good enough to... | 10,465 |
<p>I'm investigating which methods are generally used to dichotomise an ordinal variable Y so that it maximises the between-group differences in the values of X and minimises the within-group differences in the values of X. Basically I want some kind of optimal (binary) binning of my variable Y (ordinal, ranging from l... | 71,469 |
<p>I'm trying to predict in the one-way random effect ANOVA model fitted with the Gls() function of the rms package. All my attempts are unsuccessful. For instance:</p>
<pre><code># data
set.seed(421)
I <- 3
J <- 4
dd <- data.frame(y=rpois(I*J,10), group=gl(I,J))
# fit
library(rms)
fit <- Gls(y ~ 1, data=... | 71,470 |
<p>I have a dataset and I want to compute the <strong>mutual information (MI)</strong> for a selected set of variables. The dataset is large enough so that computation of the MI may take undesirably long time. <strong>Can I just take a 10% sample of the data and use it to compute the MI measure?</strong></p>
<p>I am a... | 32,926 |
<p>How can one easily and quickly grasp the idea of Bayesian statistics and modelling? I can understand the Bayesian theorem on conditional probabilities, I understand how frequentist statistics works (test statistics, p-values, hypothesis testing...), I understand <a href="http://stats.stackexchange.com/questions/2356... | 6,309 |
<p>If the effect size under analysis is too complex to allow for any other type of standard error estimate, is it appropriate to use bootstrapped standard errors to inform effect size weights?</p> | 71,471 |
<p>Suppose I have a dynamic linear model as defined in the <code>dlm</code>-package for R, see <a href="http://www.google.at/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&ved=0CD8QFjAB&url=http://cran.r-project.org/web/packages/dlm/vignettes/dlm.pdf&ei=qdyyUoPMNoqbtAa2r4DoBg&u... | 32,928 |
<p>I would like to ask a question about lags I've included however I believe it's better if I first give you some more insight information about my topic. </p>
<p>My hypothesis is ''the positive sentiment spread via Twitter can predict increasing movements on the stock market. So I've gathered approximately 60.000 'po... | 71,472 |
<p>Consider two $X$ and $Y$ that are bivariate lognormal. Is there a way to express $\newcommand{\Cov}{\mathrm{Cov}}\Cov(\log(X),Y)$ in terms of $\Cov(X,Y)$, even if an approximation must be made?</p> | 71,473 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://stats.stackexchange.com/questions/27951/when-are-log-scales-appropriate">When are Log scales appropriate?</a> </p>
</blockquote>
<p>Say you have a bar graph displaying data, for example, "Cost of Computer Orders by Population", and you are... | 49,875 |
<p><strong>Questions</strong>:<br>
1) How to detect noise variables in high dimensional data?<br>
2) Does the method that is presented below make sense?<br>
3) What clustering methods are most insensitive to random variables in data? </p>
<p>I'm made an experiment, the data was generated as follows:</p>
<ul>
<li>Num... | 71,474 |
<p>I used two different scales as a measure of social validity. I can calculate the change, but can I calculate statistical significance? Isn't my N=1? </p> | 43,829 |
<p>I have the following estimation of a two-way fixed effects model:</p>
<p>$FDI=\beta_0+ \beta_1GDP_{gr}+ \beta_2Infl+ \beta_3Realinc + \beta_4Open+ \beta_5Reserve+ \beta_6Pol_r + \beta_7Infr+ \beta_8Nat_{re}+ \beta_9SACUit+\mu_i+\gamma_i+\epsilon_{it}$</p>
<p>Where FDI is measured as net inflows of foreign direct i... | 49,244 |
<p>I'm using supervised classification algorithms from <a href="https://mlpy.fbk.eu/data/doc/classification.html" rel="nofollow">mlpy</a> to classify things into two groups for a question-answering system. I don't really know how these algorithms work, but they seem to be doing vaguely what I want.</p>
<p>I would like... | 32,935 |
<p>I would like to measure the amplitude of waves in a noisy time-series on-line. I have a time-series that models a noisy wave function, that undergoes shifts in amplitude. Say, for example, something like this:</p>
<pre><code>set.seed <- 1001
x <- abs(sin(seq(from = 0, t = 100, by = 0.1)))
x <- x + (runif... | 71,475 |
<p>I am trying to fit an ordinal regression model using the <code>logit</code> link function in R using <code>ordinal</code> package; the response variables have five levels.</p>
<p>The number of explanatory variables is much larger than the number of samples ($p \gg n$) </p>
<p>Could any one help me with the followi... | 71,476 |
<p>I am going to make an environmental index to be used as an explanatory variable in a regression model. For making this index, I asked respondents a set of questions about their environmental attitudes. Each question has 5 response options from 1=“completely agree” to 5=“completely disagree”.
I'm going to summarize ... | 43,837 |
<p>I'm really confused. I never took statistics but am trying to read up as much as I can. I didn't think much about statistical analysis until <em>after</em> doing the experiment, unfortunately, but maybe someone can help me out.</p>
<p>I have 4 birds. Each bird must fly in 7 different wind conditions. In each wind c... | 43,838 |
<p>Different implementation software are available for <strong>lasso</strong>. I know a lot discussed about bayesian approach vs frequentist approach in different forums. My question is very specific to lasso - <strong><em>What are differences or advantages of baysian lasso vs regular lasso</em></strong>? </p>
<p>Here... | 71,477 |
<p>According to normal probability distribution theory which says that for $n$ independent,
identically distributed, standard, normal, random variables $\xi_j$ the expected absolute maximum is</p>
<p>$E(\max|\xi_j|)=\sqrt{2 \ln n}$</p>
<p>Regarding this, why do we need to multiple the above-mentioned estimate by $\si... | 32,938 |
<p>I have a data set </p>
<pre><code>> head(data)
id centre u time event x c1 c2 c3 c4 c5 c6 c7 c8 c9 c10 c11 c12 c13 c14
1 1 0.729891 0.3300478 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0
2 1 0.729891 7.0100000 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0
3 ... | 43,840 |
<p>How would you get hourly means for multiple data columns, for a daily period, and show results for twelve "Hosts" in the same graph? That is, I'd like to graph what a 24 hour period looks like, for a weeks worth of data. The eventual goal would be to compare two sets of this data, before and after samplings.</p>
... | 71,478 |
<p>What is known about sampling from solutions to elliptic PDE's in high dimensions, where it is computationally infeasible to construct or store the actual solution?</p>
<p>For example, let $u$ solve the Poisson equation $\Delta u = f$ on $\mathbb{R}^n$ with the standard decay condition at infinity, and $n \approx 10... | 32,939 |
<h2>Short version:</h2>
<p>I have a time series of climate data that I'm testing for stationarity. Based on previous research, I expect the model underlying (or "generating", so to speak) the data to have an intercept term and a positive linear time trend. To test these data for stationarity, should I use the Dickey-F... | 953 |
<p>I am studying on some Machine Learning concepts. I am looking for logistic regression(multiclass) and logistic regression classifier and I should learn how to change it to penalize large weights.</p>
<p>I have looked here: <a href="http://en.wikipedia.org/wiki/Logistic_regression" rel="nofollow">http://en.wikipedia... | 71,479 |
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