question stringlengths 37 38.8k | group_id int64 0 74.5k |
|---|---|
<p>I have conducted a survey using 5-Point Likert scale (Strong Agree; Agree etc.) in which a panel of experts indicated their Agreement with suggested statements.</p>
<p>There are three sub-Groups within the expert panel</p>
<p>I am interested in evaluating the significance of Agreement for each of the different gr... | 40,444 |
<p>Gradient tree boosting as proposed by Friedman uses decision trees with <code>J</code> terminal nodes (=leaves) as base learners. There are a number of ways to grow a tree with exactly <code>J</code> nodes for example one can grow the tree in a depth first fashion or in a breadth first fashion, ...</p>
<p>Is there ... | 69,102 |
<blockquote>
<p>a random walk <strong>chooses a random bit independently</strong> and it moves left or right if the bit chosen is 0 or 1, respectively.</p>
</blockquote>
<p>I was wondering if "choose a random bit independently" means that the random bit has a uniform distribution over {0,1}, and the walk sample this... | 47,354 |
<p>Yup, I compared <code>?prcomp</code> and <code>?princomp</code> and found something about Q-mode and R-mode PCA. But honestly – I don't understand it. Can anybody explain the difference and maybe even explain when to apply which?</p> | 69,103 |
<p>I have two differing-length sequences of binary values. In each sequence, each value corresponds to an observation which is either right or wrong.</p>
<p>I'm looking for a statistical test that addresses the question "are there significantly more right answers in one sequence?"</p>
<p>Which test is most appropriat... | 69,104 |
<p>I've got a datafile which has bond returns (30, 20, 10, 5, 1 year) and time. The bond variables are returns on the different time bonds. I need to perform PCA and EFA on the data. I tried using time as one of the factors but it returns Heywood case as the uniqueness is 0. Should I disregard time? What i don't unders... | 69,105 |
<p>I'm working on implementing a logistic regression algorithm in code. It's based <a href="http://people.csail.mit.edu/jrennie/writing/lr.pdf" rel="nofollow">this link</a>. Unfortunately, the paper doesn't talk about weighting the individual examples $x_{i}$. </p>
<p>I think the relevant log likelihood function will ... | 69,106 |
<p>I am looking to find out the type of data I have and the ideal test to use calculate inter-rater reliability.</p>
<p>Research question: Functional Movement Screening: How reliable are we in our investigations?<br>
Aim: to look into the inter-rater reliability of Physiotherapists performing a functional movement scr... | 39,535 |
<p>A problem I've been toying around with:</p>
<p>Company A helps a group of students to prepare for a standardized test. A perfect score on the test is 100, but most of Company A's students receive scores between 60-90. To help their students prepare to take the real standardized test, Company A offers a series of 10... | 69,107 |
<p>What justifies the usage of a variable for post-stratification?</p>
<p>I am working with a constituent survey of a non-profit's constituent with 2500 responses out of a much larger sample and even larger population. I have <em>many</em> variables about the target population, which are all active constituents. In ... | 69,108 |
<p>One day I gave a $95\%$-confidence interval to a requester who know nothing about statistics. He asked me what does it mean. Roughly, I answered "The population parameter is inside the interval $95\%$ of times". Then he asked "And when it is outside, can it be far from the interval ?".</p>
<p>I said no but I was a ... | 29,405 |
<p>Earlier today I was discussing statistical analysis software with a colleague of mine. My colleague had primarily used SPSS in previous work for performing t-tests, anovas, manovas, and other statistical tests similar to those. My colleague also mentioned that SPSS does not handle regressions well. I have no idea wh... | 69,109 |
<p>I am involved with designing a new diagnosis method for a routine clinical procedure. I want to compare the agreement between operators to the agreement between methods. Is there such a thing as a multidimensional Kappa test, and if so how do I perform it?</p>
<p>EDIT: I could carry out a number of individual Kappa... | 29,407 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://stats.stackexchange.com/questions/41038/conditional-expectation-estimator-confusion">Conditional Expectation / Estimator Confusion</a> </p>
</blockquote>
<p>Let $X_1, X_2, X_3 \sim N(0, d^2)$ and $T = X_1^2 + X_2^2 + X_3^2.$ </p>
<p>I hav... | 49,820 |
<p>I have a large unbalanced dataset (the target has ~1500x more 0's than 1's) on which I train a logistic regression algorithm to predict the probability of success (Not a binary outcome but a real number between 0 and 1). </p>
<p>Some additional details:</p>
<ul>
<li>about 100,000,000 lines in my dataset</li>
<li>I... | 34,769 |
<p>I'm about to open the door to a very thorny issue in the social sciences. How does one correctly model and test hypotheses about mediating variables using observational data?</p>
<p>I'm familiar with the Baron-Kenny approach to mediation <a href="http://stats.stackexchange.com/questions/11971/mediation-model-with-... | 69,110 |
<p>I would appreciate it if someone could explain the concept of spurious regression intuitively / without it being too technical.</p>
<p>So far the student understands that spurious regression is basically when two processes have no relation with each other, but would still conclude that there is one using statistica... | 69,111 |
<p>I have a collection of GPS log of many vehicles. Each row has timestamp, location, speed and vehicle number. I'd like to infer to distribution of speed, or at the minimum, the portion of time they are stationary v.s. when they are moving. The vendor do not make any claim on the independence of the data. In fact, our... | 25,668 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://stats.stackexchange.com/questions/3466/best-practice-when-analysing-pre-post-treatment-control-designs">Best practice when analysing pre-post treatment-control designs</a> </p>
</blockquote>
<p>I'm doing an action research study with 2 of ... | 49,500 |
<p>I have a list of <a href="http://en.wikipedia.org/wiki/Unix_time" rel="nofollow">epoch/unix times</a> at which an event happened. My hypothesis is that there are certain times during the week when this event might happen more frequently. How can I visualize/determine which times are most probable for this event to h... | 39,219 |
<p>I have a question about ARIMA models. Let's say I have a time series $Y_t$ that I would like to forecast and an $\text{ARIMA}(2,2)$ model seems like a good way to conduct the forecasting exercise.
$$
\Delta Y_t = \alpha_1 \Delta Y_{t-1} + \alpha_2 \Delta Y_{t-2} + \nu_{t} + \theta_1 \nu_{t-1} + \theta_2 \nu_{t-2}
... | 69,112 |
<p>My chair would like me to center my data for my hierarchical multiple regression, including several moderators and interaction effects. It seems recommended to do this, if not to help minimize multicollinearity, but additionally (and more crucially) to help with interpretability of my interactions. However, where I ... | 49,325 |
<p>I am using the function McLeod.Li.test in the <a href="http://cran.r-project.org/web/packages/TSA/TSA.pdf" rel="nofollow">TSA</a> package. According to the help file in R, this function “Performs the <a href="http://www.stats.uwo.ca/faculty/aim/vita/pdf/SquaredRACF.pdf" rel="nofollow">McLeod-Li test</a> for <strong>... | 363 |
<p>How many times must you roll a non-fair die to be at least 84% sure that the sample probability will be within 3% from the actual probability.</p>
<p>Since the die is not-fair, we do not know p. My question is, can I assume it to be around 1/6, or not?</p>
<p>And so far, I found the Z-scores for 84% of the probabi... | 38,513 |
<p>I have many vectors $a_i\in\mathbb{R}^p:||a||=1,1\leq i \leq n$. I would like to test whether the $a_i$'s are randomly spread out on $S^{p-1}$ (the $p$ variate unit circle). Can anyone point to a test for that?</p>
<p>Thanks in advance,</p> | 69,113 |
<p>We always say that statistics is just dealing with data. But we also know that informatics is also getting knowledge from data analysis. For example, bioinformatics people can totally go without biostatistics. I want to know what is the essential difference between statistics and informatics.</p> | 69,114 |
<p>We're trying to develop a simple tool that will help our teams optimise their clients' Facebook posting strategies. In our experience, time of post can have a big impact on audience response; but those times will differ from audience to audience based on their behaviours (can they access Facebook from work? What tim... | 29,418 |
<p>I have some data on the number of times each of my machines turned off (due to an error) in a particular time period. There are about 6 different classes of machines being used to construct a total population of 50 machines. I wanted to analyze the stability of the 6 classes of machine relative to each other. </p>
... | 69,115 |
<p>I have some interlaboratory data where we have tested recovery weights of 3 different batches of product in three labs, with varying numbers of operators in each lab (see below).</p>
<p>I want to know whether the labs are all getting similar results. Note that we expect the three different products to have differe... | 69,116 |
<p>I am using a rank sum test to compare the median of two samples (n=120000) and have found that they are significantly different with: p=1.12E-207. Should I be suspicious of such a small p-value or should I attribute it to the high statistical power associated with having a very large sample? Is there any such thing ... | 69,117 |
<p>I am currently using the Laplace approximation to fit some geostatistical models for binomial data. Regarding parameters estimation I do not have any problem. I can easily implement the Laplace approximation and get my estimates. But when it comes to obtain the standard errors I am puzzled about how I can derive the... | 69,118 |
<p>I administer a questionnaire to managers asking them to what extent they agree / disagree that they perform certain functions (listed in the questionnaire) on a scale of 1-5. The sample functions are</p>
<ul>
<li>Setting Work Objectives </li>
<li>Providing Resources </li>
<li>Communicating </li>
<li>Organizing </l... | 69,119 |
<p>I have an un-weighted, directed graph that clusters ok using MCL or other graph clustering algorithms. However, I also have additional discrete and continuous properties of the nodes being clustered that I would like to use to get more easily interpretable clusters.</p>
<p>What are some clustering algorithms or too... | 69,120 |
<p>I'm currently in the planning stages of an experiment that I hope will detect a 0.155% signal variation (relative magnitude) within a reasonable time frame (less than 6 months ideally). I've calculated the rate of (usable) data will be around 68 events per day, though it should be stressed this is a random variable.... | 69,121 |
<p>Imagine that you want to assess the compressibility of a large document very fast. You could randomly pick a subsequence, try to compress it. This can serve as a prediction for the overall compressibility of the document. But how big should your sample be?</p>
<p>We have come up with the following strategy: </p>
<... | 69,122 |
<p>I have a variable which decays very quickly (exponentially). I want to transform it in a way it maintains "exponentially decaying" property but which will allow me to control the "speed" of a decay.</p>
<pre><code>original <- c(100, 80, 70, 65, 64, 63, 63, 63, 63, 62, 62, 61);
plot(original);
target <- c(100,... | 69,123 |
<p>I would like to fit a nonparametric regression model with two predictors.
What R packages are available?
I found 'loess' function in 'stats' package and 'gam' function in 'gam' package.
Is there anything else?</p> | 69,124 |
<p>I am using the <code>stepAIC</code> function in R to do a bi-directional (forward and backward) stepwise regression. I do not understand what each return value from the function means. </p>
<p>The output is:</p>
<pre><code> Df Sum of Sq RSS AIC
<none> 350.71 -54... | 69,125 |
<p>I would like to conduct a power analysis for a linear mixed model with fixed effects for Treatment (Two levels) and Time (four time points: pre, mid, post treatment, 3 months post treatment) and correlated random effects for children (intercepts and slopes). I am using the following code in R using the <code>lmer</c... | 69,126 |
<p>Traditionally the fitting of the logistic regression function is explained using maximum likelihood. Could one fit the logistic regression function as well based on either least-squares or based on misclassification error, or is this not possible / has drawbacks? </p> | 29,435 |
<p>I implemented the classical scaling and obtained the relative coordinates in Java.<br>
I want to translate these relative positions, but I am not getting how I should be doing this.</p>
<p>This is just like:</p>
<pre><code>T (x, y) =
(x y) (0.981 −0.196
0.196 0.981) + (0.016 − 0.835)
</code></pre>
<p>The... | 69,127 |
<p>I belong to a new <a href="http://www.toastmasters.org/" rel="nofollow">Toastmasters</a> club that is growing quickly. We meet twice a month and each meeting has four opportunities (slots) for members to give prepared speeches.</p>
<p>As more members vie for the available slots, we're looking at ways to respond to ... | 69,128 |
<p>I have a problem whereby I get two different answers if I try to maximize a function.</p>
<p>let
$ \begin{bmatrix} Y_{o}\\ Y_{a} \end{bmatrix}|\phi\sim N (0,\phi^{-1}A^{-1}) $</p>
<p>$\pi(\phi)=\frac{1}{\phi}$,</p>
<p>where $Y_{o} \in \mathbb{R}^{n_{o}}$, $Y_{a} \in \mathbb{R}^{n_{a}}$</p>
<p>I am trying to fin... | 69,129 |
<p>This problem is 9.56 from Casella-Berger. </p>
<p>Let $X \sim f(x|\theta)$ and suppose that we want to estimate $\theta$ with an interval estimator $C$ using the loss $$L(\theta, A) = bLength(A(X)) - I(\theta \in A(X))$$
If $\theta$ has the prior pdf $\pi(\theta)$, show that the Bayes rule is given by
$$ C^{\pi} =... | 17,505 |
<p>Provided a sample size S that I plan on using to forecast data. What are some of the ways to subdivide the data so that I use some of it to establish a model, and the remainder data to validate the model?</p>
<p>I know there is no black and white answer to this but it would be interesting to know some "rules of th... | 69,130 |
<p>I want to represent a variable as a number between 0 and 1. The variable is a non-negative integer with no inherent bound. I map 0 to 0 but what can I map to 1 or numbers between 0 and 1?</p>
<p>I could use the history of that variable to provide the limits. This would mean I have to restate old statistics if the m... | 29,447 |
<p>I have computed percentage change from time1 to time2 for several variables.</p>
<p>Can I predict percentage change in earnings from percentage change in produced and percentage changed in price?</p>
<p>When I ran a model with actual data and dummy coded time (time1=1, time2=0), the dummy variable was not statisti... | 29,448 |
<p>Here are four different sets of numbers:</p>
<p>A = {95.47, 87.90, 99.00}<br>
B = {79.2, 75.3, 66.3}<br>
C = {38.4, 40.4, 32.8}<br>
D = {1.8, 1.2, 1.1} </p>
<p>Using a two-sample t-test without assuming equal variances, I compare B, C, and D to A and get the following p-values:</p>
<p>0.015827 (A vs B)<br>
0.00... | 46,340 |
<p>I have some data that I'd like to apply classification to:</p>
<pre><code>Label Start1, End1, Start2, End2, Start3, End3
0 range 1 range 2 range 3
1 ...
2 ...
1 ...
...
</code></pre>
<p>SVM seems like a good approach for this particular type of data, but I'm not v... | 29,450 |
<p>I was wondering if anyone had experience using the mice function, as described in <a href="http://www.jstatsoft.org/v45/i03/paper" rel="nofollow">mice: Multivariate Imputation by Chained Equations in R</a> (JSS 2011 45(3))? I have a dataset with a number of variables, each with varying degrees of missing data. </p>
... | 69,131 |
<p>I would like to generate conditional correlated random variables. I have a correlation matrix between normal variables, and these variables are modeled through SDEs. </p>
<p>What are the algorithms to generate such random values? One example I found is;
<a href="http://www.mathworks.com/help/toolbox/econ/interpolat... | 38,668 |
<p>I am working through Bishop's book PRML.
I have been stuck on question 6.18, for a while and would appreciate some guidance.
I feel like I am fundamentally not understanding something. </p>
<p><img src="http://i.stack.imgur.com/MgKDe.png" alt="enter image description here"></p> | 69,132 |
<p>Does anyone know of any method for deciding when a genetic algorithm is done? In MCMC (e.g, BUGS), several chains are started at different, random points. When they all look the same, it is done. Has this approach ever been tried with GA? Any other ideas? </p>
<p>thanks</p> | 37,732 |
<p>I have a question. Here it is guys.</p>
<blockquote>
<p>How do you use R from the command line?</p>
</blockquote> | 39,606 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://stats.stackexchange.com/questions/26352/pca-analysis-with-centered-variables">PCA analysis with centered variables</a> </p>
</blockquote>
<p>In my PCA analysis I have in a component both negative and positive variables. This is probably ve... | 49,821 |
<p>I have a dataset where one variable is a proportion with a restricted range (say 4%). I would like to use this variable to predict a death rate. Running a simple correlation I'm guessing would underestimate the relationship (?). I also have raw counts for both variables. What analysis do I do here? I'm stuck. Binomi... | 69,133 |
<pre><code>libsvm 3.18
Features: 10
</code></pre>
<p>I have used following, parameter range:</p>
<pre><code>C-parameters: 2^-3 , 2^-2 .. 2^11,
g-parameters: 2^-11 , 2^-10 .. 2^-3,
</code></pre>
<p>with <code>10-fold</code> cross validation(-v 10).</p>
<p>Maximum <code>accuracy(81.8646%)</code> at <code>c-value 20... | 69,134 |
<p>I am looking for help on post-hoc test of my group data (treatment and stage and interaction) after 2 way anova in R software. The data shown below is a example only actually my data shows significant result after ANOVA test. When I tried post hoc with TukeyHSD it gives pair wise comparisons which is a long list. Bu... | 69,135 |
<p>I am in the midst of programming a simple Naive Bayes classifier as an exercise. It is supposed to perform word-sense disambiguation on natural language phrases, e.g. predicting the correct meaning of the ambiguous word <em>bass</em> in a sentence like <em>I love the taste of bass</em>.</p>
<p>At the moment I am st... | 69,136 |
<p>I have a data frame like this:</p>
<pre><code> period x y db perc
1 2013-08-26 4 166 nh 2.409639
2 2013-09-02 5 222 nh 2.252252
3 2013-09-09 3 223 nh 1.345291
4 2013-09-16 9 198 nh 4.545455
5 2013-09-23 3 213 nh 1.408451
6 2013-09-30 5 226 nh 2.212389
...
</code></pre>
<p>There are many observations per... | 69,137 |
<p>Hello after struggling with using R for the last couple of days I was hoping someone could help me with a statistical analysis I am completing for an environmental science honours project. Using R statistics is not something we have been taught and I am worried that I may have bitten of more then I can chew, however... | 39,609 |
<p>I have been set the following question as part of homework:</p>
<blockquote>
<p>Design and implement a simulation study to examine the performance of the bootstrap for obtaining 95% confidence intervals on the mean of a univariate sample of data. Your implementation can be in R or SAS.</p>
<p>Aspects of perf... | 39,610 |
<p>I have a data set that consists of 143 variables (~11000 observations), and I wish to do variable clustering to reduce the dimension. I am using <code>hclustvar</code> function in R from <code>ClustOfVar</code> package. After performing the hierarchical clustering using <code>tree <- hclustvar(X)</code>, I wish t... | 69,138 |
<p>I have a dataset that includes one independent variable with 3 levels (group 1, group 2, and group 3) and a repeated dependant variable (pre test score, post test score).</p>
<p>I am using the statistics package SPSS and when I took the method I thought I would use "repeated measures anova" there didn't seem to be ... | 39,611 |
<p>I have a problem where I get data from 3 different sources <strong>s1, s2, s3</strong>, and I have the target (<strong>value</strong>). I might have missing values from some of the predictor variables at certain rows. This is the structure of my data set:</p>
<pre><code>s1 s2 s3 | value
--------- ------
34 23 34 | ... | 69,139 |
<p>I'm running a statistical analysis for work in which I'm trying to determine which (if any) key economic indicators influence our sales. Here is the summary data that I'm getting when I run a multiple regression:</p>
<p><img src="http://i.stack.imgur.com/GQseA.jpg" alt="enter image description here"></p>
<p>It ap... | 69,140 |
<p>In a book it is written that,</p>
<p>In regression work we typically assume that the observational errors are pairwise uncorrelated. But in most time series data , the successive residuals have tendency to correlated with themselves.If we find autocorrelated errors, we need to modify the regression procedure to re... | 29,461 |
<p>What are the gold standard datasets to test market segmentation algorithms with? I'd like to try a few algorithms on known datasets for comparison before I try my own dataset.</p> | 22,602 |
<p>You have multicollinearity when you have 2 variables $(X_1, X_2)$ that have a relationship, $X_1=a+X_2$ where $a$ is constant. My question is: is there still a multicollinearity issue if $a$ is not constant, $X_1=X_3+X_2$? For example your testing children and you have their birthday and the date of the test, so <co... | 69,141 |
<p>We have a bivariate normal process where $X, Y \sim N(0, \sigma)$, with no covariance.</p>
<p>(For convenience we can assert that $\sigma = 1$, or that we have a good estimate for its value.)</p>
<p><strong>What is the distribution of the random variable $R(n) = \sqrt{\overline{x_i}^2 + \overline{y_i}^2}$ —... | 69,142 |
<p>Consider the model </p>
<p>$q_t^d\;=\;\alpha_0+\alpha_1p_t+\alpha_2y_t+e_t\\
q_t^s\;=\;\beta_0+\beta_1p_t+\beta_3z_t+u_t\\
q_t^d\;=\;q_t^s$</p>
<p>where $p_t$ is endogenous and $y_t$ and $z_t$ are exogenous. Suggest how to test</p>
<p>$H_0\;:\;\alpha_2=\beta_3=0 \\
H_A\;:\;\alpha_2\neq0,\:\beta_3\neq0$</p>
<p>I... | 29,463 |
<p>I would like to use cross-validation to test how predictive my mixed-effect logistic regression model is (model run with glmer). Is there an easy way to do this using a package in R? I've only seen cross validation functions in R for use with linear models.</p> | 49,822 |
<p>I have a lot of data on previous race history and I'm trying to predict a percentage chance of winning the next race using Regression, kNN, and SVM learning algorithms.</p>
<p>Say a race has 5 runners, and each runner has a previous best course time of, say $T_i$ (seconds).</p>
<p>I've also introduced an additiona... | 69,143 |
<p>I am using the coin package in R to do a permutation test and it gives output that looks like this:</p>
<pre><code>> pvalue(pt)
[1] 0.1479615
99 percent confidence interval:
0.1450811 0.1508754
</code></pre>
<p>Why would one want a confidence interval for a p-value? How should it be interpreted, and how should... | 29,465 |
<p>Questions in respect to rotation post-PCA have been answered before -> its all in the hands of the researcher... Same answer to the question if rotation (orthogonal or not) makes sense before plugging the components into a cluster analysis?</p> | 69,144 |
<p>Why are residuals usually autocorrelated in time-series data? Could it stem from the autocorrelation of the response variable? Is the reason that in some cases the differencing (i.e., the differences between adjacent values of the response variable) is used?</p> | 69,145 |
<p>In R, I am trying to write a function to subset and exclude observations in a data frame based on three variables. My data looks something like this:</p>
<pre><code>data.frame': 43 obs. of 8 variables:
$ V1: chr "ENSG00000008438" "ENSG00000048462" "ENSG00000006075" "ENSG00000... | 47,591 |
<p>Following is Example 4.1.4 from Bickel and Doksum's mathematical statistics book. Given an iid sample $X_1, ..., X_n$. each $X_i$ has a Bernoulli distribution with unknown parameter $\theta$.</p>
<p>Given a constant $\theta_0$, we want to test $H: \theta=\theta_0$ versus $K: \theta >\theta_0$.</p>
<p>The test s... | 39,638 |
<p>I have created a simple scatterplot to analyse the correlation between two variables, x and y. Using the abline command, I added a trendline to this data. I now want to know the formula for this trendline. Is there a command that will give this formula as one is able to do in a simple Excel scatterplot? </p> | 37,983 |
<p>For a two-way repeated measures design, we can specify the model using <code>aov</code> in the following fashion:</p>
<pre><code>aov(dv ~ iv1 + iv2 + Error(subject/(iv1*iv2)), data=dataset)
</code></pre>
<p>Take the sample data from <code>personality-project.org</code> (see code below), the error term for this par... | 29,469 |
<p>Could somebody please explain why <a href="http://www.ats.ucla.edu/stat/mplus/seminars/introMplus_part2/path.htm" rel="nofollow">this</a> model is "just identified"</p>
<p><img src="http://i.stack.imgur.com/yRCmk.png" alt="enter image description here"></p>
<p>As I see it, there are 5 * 4 / 2 = 10 variances/covari... | 69,146 |
<h2>Problem setup</h2>
<p>One of the first toy problems I wanted to apply PyMC to is nonparametric clustering: given some data, model it as a Gaussian mixture, and learn the number of clusters and each cluster's mean and covariance. Most of what I know about this method comes from video lectures by Michael Jordan and ... | 69,147 |
<p>I have created a scatterplot. I want to see the trend of how the number of fishing cat scats vary with an increase in perimeter of water body. Hence my response variable is <code>number of fishing cat scats</code> and predictor variable is <code>perimeter of water body</code>. After creating a scatterplot, I gave an... | 29,472 |
<p>I'm doing survival analysis and I have three time-dependent variables, with different time scales each. I've already done univariate analysis and I want to proceed with multivariate analysis.</p>
<p>My questions is how can I choose or deal with different time-scales?</p>
<p>I'm using R, survival package.</p> | 69,148 |
<p>Consider that $P$ is the water pressure coming out of a valve $A$. Let $P_{dif}$ be the difference between the maximum and the minimum pressure of valve $A$: </p>
<p>$$P_{dif}≔P_{max}-P_{min}$$</p>
<p>Now, what I want to do is estimate $P_{dif}$. In order to do that, I take a number of water pressure samples from ... | 29,473 |
<p>What would be a good book for non-parametric statistics. Not just the introduction but advanced level. Also I am looking at something I can use for learn and not for reference.</p>
<p>In particular I am looking for a book that can contain basics behind non-parameteric methods, non-parameter inference, methods to ev... | 41,458 |
<p>I have a symmetric matrix $V$ of order 10. I want to decompose $V$ in such a way that $$V=SS'$$ with $S$ being non triangular. The matrix $S$ has some restrictions that 45 cells have ‘0’ values and 55 other remaining cells are supposed to be solved.</p>
<p>I am looking for solving this using sas.</p>
<p>Here is t... | 69,149 |
<p>If $X$ is a $m × n$ matrix, where $m$ is the number of measurement types (variables) and $n$ is the number of samples, would it be correct to perform a PCA on a matrix that has $m \geq n$ ? If not, please provide some arguments why would this be a problem.</p>
<p>I remember having heard that doing such an anal... | 47,592 |
<p>I'd like to check if my observations are normally distributed by using a chi-square plot. To calculate the generalized squared distances (squared Mahalanobis distances) I need the covariance matrix of my observations.</p>
<p>Is it correct that I have to use the <a href="http://en.wikipedia.org/wiki/Sample_mean_and_... | 11,790 |
<p>I was asked to implement an Ornstein-Uhlenbeck process in one of my simulations. I have coded the process to visualize the results and I was wondering, if my first value is at the mean, why bother using an O-U process? I thought the advantage of an O-U process is that it is mean-reverting, but if I am starting at th... | 29,481 |
<p>Here are 3 questions about econometrics and <code>R</code> codes.</p>
<p>Test the endogeneity of the variable EDUC:</p>
<pre><code>etudes1 <- lm(EDUC ~ EXPER+EXPERSQ+SMSA+SOUTH+FATHEDUC+MOTHEDUC, data=Dataset)
Call:
lm(formula = LWAGE ~ EDUC + EXPER + EXPERSQ + SMSA + SOUTH + residuals(etudes1))
Residuals:
... | 69,150 |
<p>Actually, my question may just be about cross-validation in general. Here's what I'm doing: I'm trying to come up with a model using scikit-learn to learn on some data I've got. I've decided to use an SVM, using various kernels, to do the modelling. I've got about 50,000 data points from which to extract features. I... | 69,151 |
<p>Salmon were collected and induced to spawn. The percent of the fish collected who spawned successfully was 63%, so P(S)=0.63. A sample of the eggs were then fertilized and the percent of eggs that were successfully fertilized was 70%, so P(F|S)=0.70. The fertilized eggs were allowed to hatch and the percent of fe... | 69,152 |
<p>My experimental setup is the following: </p>
<ol>
<li>compute an optimal solution $S$ to problem $A$ on instance $I$,</li>
<li>evaluate test statistic $f(S)$,</li>
<li>compute $f(S_i)$ for $S_i$ $(0 \leq i \leq n)$ drawn from a uniform distribution of feasible solutions to $A$, and</li>
<li>compute a p-value for S... | 69,153 |
<p>If I have a questionnaire with items on a Likert scale (1 to 5) and a sixth option "I do not know/Does not apply", is it okay to consider a "I do not know/Does not apply" response as a missing value and use an imputation method, just like I would consider and impute the missing values in the case when respondent to ... | 69,154 |
<p>I have a data of 30 values that represent returns on investment and which have a mean of 7 and standard deviation of 14. We are talking here about normal distribution. Now I am being required to do a following: </p>
<blockquote>
<p>If you are given a choice between the top 6% of returns and a return of 25%, which... | 909 |
<p>01 August 2014
11:17</p>
<p>Hi,</p>
<p>I have 5 measures repeated 3 times under 3 different scenarios (conditions). The measures are survey questions and participants use a visual analogue scale to mark a response from 0.0 to 15.0. The same 5 measures (questions) are repeated for each of the 3 scenarios (conditi... | 69,155 |
<p>I now that one can use Seemingly Unrelated Regressions when for an observation i, there are two equations whose errors are connected. </p>
<p>What is the intuition here among errors of difference equations have some sort of relationship? In the SUR case, is it simply because unobservable factors (say, for example, ... | 29,485 |
<p>Suppose I have $N$ independent random variables $X_n$. I draw a sample of predetermined size $K_n$ from each of them. Denote the average of each sample $\bar{\hat{X}}_n$, and the total number of observations $M = \sum_{n=1}^{N} K_n$.</p>
<p>Next, I use all the $M$ sample observations $\hat{X}_{n,k}$, with no regard... | 69,156 |
<p>First set: 12, 23, 24, 14, 29, 30, 31, 16.
Second set: 12, 22, 24, 14, 30, 30, 31, 16.
These data are obtained using a software (first set) and visual observation (second set) of the same process. I do not know if it matters it is expressed in minutes per 2 hours interval.
Thanks.</p> | 39,652 |
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