question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<blockquote>
<p>Let $X_1, ... , X_n$ be iid with common density $f(x) = ax^{a-1}$, $ 0 < x < 1$, where $a$ is an unknown parameter $a > 0$. </p>
<p>(a) Find the MLE for $a.$</p>
<p>(b) Show that $W = - \sum^n_{i=1} \ln X_i$ has a Gamma distribution with parameters $\alpha = n$, $\beta = 1/a$. Hint:... | g60031 | [
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<p>I'm working with autoKrige and Gstat. I was wondering if it's possible to add to two differents models like Exp with Gau. </p>
<blockquote>
<p>I know if I put something like this "kriging_result<-autoKrige(z~1,data,grid,model="Sph",fix.values = c(0,NA,NA))"
the program uses that model to fit the variogram, ... | g60032 | [
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<p>Say you've got a simple cross-sectional model
$$
y=\alpha + \beta T +\epsilon
$$
where $T$ is binary. This is basically a t-test, but lets treat it like a regression. </p>
<p>You're interested in the effect of $T$ on the first and second moments of the outcome. (You might have done GLS or IRLS as well, though my... | g60033 | [
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<p>I was reading this paper where it is mentioned</p>
<p>Let F(·) be the CDF of a continuous random variable X and $\phi^{−1}(·)$ be the inverse of the CDF of N(0,1). Consider the transformation from X to Z by Z = $\phi^{−1}(F(X))$. Then it is easy to see that Z is standard normal regardless of F</p>
<p>I didn't get ... | g60034 | [
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<p>I'm familiar with basic regression methods, but have no experience using GEEs. I use SPSS, and I'm trying to use a GEE for a dataset that I have, because there is a repeated measures component in my model. </p>
<p>Anyway, in my model, I have 3 dichotomous predictors (let's say, $x_1$, $x_2$, and $x_3$), as well as ... | g60035 | [
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<p>If I fit a time series with a AR model, I can tell if this fit is valid by checking the residual correlation (valid if not correlated). </p>
<p>But if I fit it with a MA model, how do I tell if this fit is valid or not? In R, when I specify to fit the time series with, say MA(1), it will automatically use white noi... | g60036 | [
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<p>I am considering two linear models with model matrices related as follows:</p>
<p>\begin{equation*}
\text{Model} \ 1 \\
\begin{bmatrix}
\mu_1 \\
\mu_2 \\
\vdots \\
\mu_n
\end{bmatrix}
=
\begin{bmatrix}
1 & x_{12} & x_{13} \\
1 & x_{22} & x_{23} \\
\vdots & \vdots & \vdots \\
1 & x_{n2} &... | g15921 | [
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... |
<p>Is it viable to do several binary logistic regressions instead of doing a multinomial regression? From this question: <a href="http://stats.stackexchange.com/questions/52104/multinomial-logistic-regression-vs-binary-logistic-regression">Multinomial logistic regression vs binary logistic regression</a> I see that the... | g15922 | [
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<p>I am quite rusty on my stats beyond standard deviation and linear regression, so I am not even sure about how to phrase this question.</p>
<p>I am looking at a long history of credit card qualification data, so I know how much money has been processed as rewards cards, AMEX, World cards, etc. I have this data for e... | g60037 | [
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<p>Can someone think of joint distribution of random variables X, Y such that the following three
conditions are satisfied: </p>
<p>$E[X] = 1$,<br>
$E[Y] = 1$, and<br>
$E[XY] = 0$? </p>
<p>A friend of mine asked me this, which seems simple, but I'm not a stat whiz, so This makes my head spin. Thank you for answeri... | g60038 | [
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<p>Are there any rules to calculating mean percent or is it the same as calculating any other average (i.e., add all of the percents together and divide by the sample size)?</p> | g60039 | [
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<p>I have the two following questions:</p>
<ol>
<li><p>Imagine I have two sets of observations, and both sets have a lognormal distribution. Now, given I look at the union of the two sets - is the distribution still a lognormal?</p></li>
<li><p>Given now I have again a set of observations with lognormal distribution. ... | g41734 | [
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<p>Having the marginal distributions, say $f(x)$ and $f(y)$, how would we get the conditional distribution $f(x|y)$? The relation is given by:
$$f(x)=\int f(x|y)f(y)dy$$
Do we need to find the derivatives of both sides and then solve a differential equation?! </p> | g15928 | [
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<p>I am running a hierarchical model in JAGS. It is a piecewise constant survival regression model.</p>
<p>So I have 4 sets of regression coefficients and baseline hazard rates.</p>
<p>I would like to plot a mean curve and range using the mean and 95% highest density interval (HDI) of these parameters using the covar... | g45332 | [
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<p>Does anyone know where can I find a pseudo code or MATLAB code of the HMM forward algorithm? </p> | g37666 | [
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<p>What are the pros and cons of learning about a distribution's properties algorithmically (via computer simulations) versus mathematically?</p>
<p>It seems like computer simulations can be an alternative learning method, especially for those new students who do not feel strong in calculus.</p>
<p>Also it seems that... | g60040 | [
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<p>I have data with standard error, included below for clarity,</p>
<pre><code> X Y Error in Y
0.0105574 -28.831027 0.04422
0.0070382 -27.800385 0.04225
0.0052787 -27.314088 0.04209
0.0042229 -27.054207 0.04185
0.0035191 -27.000188 0.04143
0.0030164 -26.8... | g15934 | [
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0.03... |
<p>I am working on a story problem for a project. </p>
<p>"You work for a small environmental foundation that wants to analyze fuel consumption. Your boss (in the year 2002) has asked you to help her analyze the 2001 data on highway fuel consumption to find out what a change in the tax rate does to fuel consumption. S... | g60041 | [
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<p>I have to generate random numbers for my algorithm based on probability distributions. I want a distribution which has heavy tails and is unskewed, which can produce numbers far away from location parameter. There should be a parameter to control the tail heaviness (e.g., like levy distribution where alpha determine... | g60042 | [
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<p>I am trying to predict labels for a test set (around 15000 instances of around 400 features) based on a model trained with a training set (around 86 instances of around 400 features).</p>
<p>I am using Weka 3.6.11 on a humble Windows laptop.</p>
<p>Both training and test set are loaded from a .csv file (one file f... | g60043 | [
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<p>Does the equation below have a name, or is it similar to some other well-known process/ equation?</p>
<p>Equation of interest:</p>
<p>$$S_c = S_{c-1} + S_{c-1}\omega_c\delta_c$$
$\delta\sim\mathcal{N}(0,1)$ is a standard normal shock</p>
<p>$\omega\sim\mathcal{B}(1,~0.5)$ is a coin flip with a 50% chance of being... | g60044 | [
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-0.0... |
<p>I have energy consumption data from a device for the past two weeks.</p>
<p>I have to predict energy consumption of this device for another week. </p>
<p>I am not sure how to forecast this.</p>
<p>Does anybody know how to do that?</p>
<p>If there a way to do that in R? I've just started learn the R language. </p... | g15942 | [
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<p>I have three variables which I want to combine in one. The obvious choice is factor analysis or principal component analysis but it's not so simple with panel data because it needs means and standard deviations and in absence of information about panel structure, software calculates the mean and sd for the whole poo... | g60045 | [
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<p>Is there a package that implements Maxent Markov Models in R? (<a href="http://en.wikipedia.org/wiki/Maximum-entropy_Markov_model" rel="nofollow">http://en.wikipedia.org/wiki/Maximum-entropy_Markov_model</a>).</p>
<p>I understand that package crf implemets conditional random fields which are related, and there are ... | g60046 | [
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<p>I conduct some experiments on continuous speech recognition. After the initial application of the recognizer I have the phoneme sequence that includes some errors (three types of errors: substitution, deletion and inclusion). For instance:
I obtain</p>
<p><em>h e l' l o n y k f r a n d s t</em></p>
<p>instead of</... | g27833 | [
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<p>My question is about analysis of signals with PCA in the frequency domain.</p>
<ul>
<li>As frequency analysis offers a powerful tool for signal processing, does Principal Component Analysis (PCA) have any "well-known" advantages or usages in the frequency domain? </li>
<li>Can it be stated that PCA is doing a kind... | g15948 | [
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<p>The first one is from <a href="https://class.coursera.org/ml-005/lecture/11" rel="nofollow">Andrew Ng</a></p>
<p><img src="http://i.stack.imgur.com/JNfEv.png" alt="enter image description here"></p>
<p>The second one is from <a href="http://www.ann.jussieu.fr/~plc/bach2012.pdf" rel="nofollow">Francis Bach</a>
<img... | g60047 | [
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<p>If you want to estimate $E[y| x = \text{some value}]$ is this just a matter of plugging $x$ into the regression equation?</p>
<p>Because you estimate the regression coefficients, therefore the value you get is an estimate also?</p> | g15949 | [
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<p>I don't know whether this is a pure statistics, math or programming question so kindly let me know if there is a better place to post this question.</p>
<p>I am trying to implement the <a href="http://en.wikipedia.org/wiki/Compartmental_models_in_epidemiology#The_SIS_model" rel="nofollow">SIS epidemic model</a> whe... | g60048 | [
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<p>I have a question regarding interactions in GLM.
I run a Poisson regression with the purpose of predicting claims in insurance.</p>
<p>I have the following problem :</p>
<pre><code>model 1 : CLAIMS ~ X1 + X2
model 2 : CLAIMS ~ X1 + X2 + X1:X2
</code></pre>
<p>X1 has 10 levels, X2 has 4 levels</p>
<p>When I do a ... | g60049 | [
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-0.013079170137643814,
0.01772712916135788,
0.01839941181242466,
-0.... |
<p>Let $x_i$ be independent Bernoulli random variables with success probabilities $p_i$. That is, $x_i=1$ with probability $p_i$ and $x_i=0$ with probability $1-p_i$.</p>
<p>Is there a closed expression or an approximate formula for the distribution of the sum $\sum_i x_i$?</p> | g49579 | [
-0.0316513292491436,
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0.046645015478134155,
0.023519648239016533,
0.0... |
<blockquote>
<p>a) For which of the following observations (obs1, obs2, obs3) is the variance of the residual the largest? Which observation has the highest leverage? And which one the smallest? Explain why.</p>
<p>b) Which of the three observations has the largest DFBETAS?</p>
<p>c) About which observation... | g60050 | [
0.014941917732357979,
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0.006539202760905027,
-0.... |
<p>I'm running a regression on independent variables, some of which are measured in different units, for example:</p>
<ul>
<li>The amount of broadband connections in a country</li>
<li>The amount of broadband connections in a country per 100 people</li>
</ul>
<p>Since the second is not perfectly correlated with the f... | g45357 | [
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0.007534049451351166,
0.007688385900110006,
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<p>There is many variants of type of solver in <a href="http://www.csie.ntu.edu.tw/~cjlin/liblinear/" rel="nofollow">liblinear</a> but I don't understand their differences.Which one I must choose?</p>
<p>Also why data must be scaled? duo to some numerical issues?</p>
<blockquote>
<pre><code>-s type : set type of solv... | g27114 | [
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0.06395695358514786,
0.060... |
<p>I sense this is not a good idea, but am struggling to think of an reason why it is wrong, other than that the assumption of homogeneity of variances would surely be violated. Is there some more fundamental reason why this is wrong?</p>
<p>Does it depend on how many participants are in the other levels of the factor... | g60051 | [
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0.... |
<p>From John Kruschke's <a href="http://www.indiana.edu/~kruschke/DoingBayesianDataAnalysis/" rel="nofollow">book</a>, Chapter 7, Pg. 120 (summarised for succinctness):</p>
<blockquote>
<p>A politician is constantly travelling from island to island on a chain
of islands... His goal is to visit all the islands prop... | g27835 | [
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0.00405657896772027,
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0.... |
<p><img src="http://i.stack.imgur.com/sX1yH.png" alt="enter image description here"></p>
<p>Here I have shown the first two lines of my data frame. It goes on for a number of lines.</p>
<p>I am wanting to make plots to show what is happening over time . e.g a plot showing the sequence of grip changes over time and wh... | g20062 | [
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<p>I have 2 studies looking at the patient response to the same drug. Study 1 found 10,000 genes expressed above the background and 500 of them are differentially expressed and referred to as the drug response signature. Study 2 found 1,000 genes representing the drug response signature. The overlap between the two sig... | g60052 | [
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<p>I have a sparse regression problem (Sparse because a few inputs are factors so we have a lot of columns of 1s and 0s). I am thinking of Ridge Regression because of the sparsity, but also because a lot of the terms will have interaction effects. I also want an interpretable model.</p>
<p>Is there a way to use the Ri... | g60053 | [
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0.0351... |
<p>I have a noisy readout of a curve that is monotonically increasing or decreasing for a narrow range of points and then quickly saturates. I don't know exactly where the saturation point is, but from the underlying (biological) process I know that it exists and once it's reached, strong deviations from a flat line ar... | g60054 | [
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0.01688949018716812,
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<p>This is a simple question on Bayesian spatial modelling via conditional autoregressive modelling. </p>
<p>What is, according to your judgement (and possibly some methodological source), the minimum number of regions for which CAR is suitable? Would you say that with a low number of regions, say 9, it is highly advi... | g60055 | [
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<p>I have a system to which I make certain changes. I want to compare the impact of those changes on the system performance. For this, I record the performance as a function of a set of inputs multiple times, before and after the changes have been made. How do I quantify the impact of these changes given that random en... | g15959 | [
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0.036451879888772964,
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0.050527505576610565,
0.04558170586824417,
... |
<p>Please consider the following excerpt from "Measuring and Explaining Competition in the Financial Sector" by Bikker and Spierdijk (2008):</p>
<blockquote>
<p>"In many economic theories, competition is related to the (relative) size of a mark-up on
the cost price as a component of the output price. However, data... | g60056 | [
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0.004471389576792717,
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0.027311697602272034,
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... |
<p>I am attempting to implement a Kalman filter in R. Working from "Time Series Analysis" by Hamilton the state space equations are defined as:</p>
<p>State: $z(t) = F_z(t-1) + v(t)$</p>
<p>Observation: $y(t) = A'x(t) + H'z(t-1) + w(t)$</p>
<p>Where $x(t)$ are exogenous variables. The model I am attempting to impl... | g60057 | [
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0.018052972853183746,
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... |
<p>Imagine such a memory test for a mice. The mice performs an experiment $E$ with two possible issues $0$ (failure) and $1$ (success). If the mice gets $1$ it is "rewarded", if it gets $0$ it is "punished".</p>
<p>The experiment $E$ is repeated many times with the same mice, and we consider the stochastic process $(X... | g60058 | [
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0.03177538886666298,
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0.026375971734523773,
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0.03... |
<p>I have a data set that includes the different response times of a user that is visiting a web application.
For example, a visitor enters www.test.com in the browser and navigates through this domain watching child pages like www.test.com/news, www.test.com/overview, www.test.com/overview/current, etc. If a user watc... | g4 | [
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0.002976442454382777,
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0.020326266065239906,
0.01901322975754738,
0.014... |
<p>In GEE, the variance of each outcome is equal to the variance function multiplied by the scale parameter. For a continuous outcome the variance function =1. I understand that the scale parameter for a continuous outcome is always estimated in a GEE analysis, as opposed to set at 1 as for a poisson or binary outcome... | g21829 | [
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0.007791886571794748,
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<p>I have a simple dataset of people's heights, many people with measurements on multiple days (once a year for 10 years, say). I have the date of each measurement.</p>
<p>Some of the height values are absurd. I already drop values that are 'impossible' (e.g. height values above 3m). However, I'd like to identify u... | g15962 | [
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0.020112255588173866,
0.022503849118947983,
0.0432150661945343,
-0.00... |
<p>Suppose you impute a variable using a normal distribution with mean 10 and sd 5. Is it better to draw 1000 random samples from this normal distribution, take the average, and then use this to impute this missing value? Or can I just take one draw from this distribution and use this as the value to impute the missing... | g18314 | [
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0.011285127140581608,
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0.0031300929840654135,
0.029913663864135742,
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0.02864132635295391,
-... |
<p>I would like to use a greedy nearest neighbour method to do propensity score matching. Though I've little experience here, it seems that the distance measure used is generally a propensity score generated from a logistic regression. My question is: why logistic regression? Why not a random forest, SVM or another met... | g60059 | [
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0.04540606215596199,
0.018205586820840836,
0.039248183369636536,
0.027... |
<p>Are there any Machine Learning/ Datamining research paper which deals with predicting the performance of two team containing each $x$ players?</p> | g15964 | [
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-... |
<p>Pearson's $\chi^{2}$ value is 115.778 and 4 cells (33.33%) have expected count has less than 5. I am confused how to interpret this output. I have a 2 by 6 contingency table. Can someone tell me what has gone wrong?</p> | g60060 | [
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0.01100126001983881,
0.02085106261074543,
0.0063521829433739185,
-0.00... |
<p>Is there any problem if we use too many hidden layers in Neural Network? Can anyone simply describe what problems can occur if we have too many hidden layers.</p> | g33867 | [
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0... |
<p>I am attempting to build a model a for which the only valid output in the range [0,100]. I was wondering if would be possible to reduce the penalty on values under 0 and over 100 as they will be constrained anyway in order to get a better fit.</p> | g60061 | [
-0.027701275423169136,
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<p>I am trying to find out the rejection region for a permutation test about the difference between medians where:</p>
<pre><code> H0: Difference between medians equals 0;
Ha: Difference between medians is greater than 0.
</code></pre>
<p>Considering that I have the distribution of my test statistics on resampled ... | g15966 | [
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0.058611251413822174,
0.06161002814769745,
... |
<p>What should one do, if the parameters for a logistic regression model are significant as well as the model itself, but the test for the goodness of fit show that the model is bad (i.e. the P-values of deviance etc. are low)? </p> | g44629 | [
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0.04721749573945999,
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<p>Note: I do not have access to <code>SAS</code> to work this out for myself.</p>
<p>I'm trying to work out the difference between the <code>FREQ</code> statement in <code>PROC GENMOD</code> (for example) and the <code>REPLICATE</code> statement in <code>PROC NLMIXED</code>.</p>
<p>The <code>SAS</code> explanation i... | g45370 | [
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0.014429373666644096,
0.02633151039481163,
0... |
<p>I have three years of infection data from 6 different hospitals. </p>
<pre><code> 2010 2011 2012
1 1.3 2.5 1.03
2 3.35 2.5 2.6
3 4.1 1.8 2.5
4 2.0 3.65 .7
5 3.4 3.75 2.4
6 1.2 3.4 1.3
</code></pre>
<p>These numbers are ... | g41371 | [
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0.014187945984303951,
0.04580383747816086,
0.0026057232171297073,
0.029303131625056267,
0.0... |
<p>Suppose I have a mutivariate Gaussian distributed variable $u\sim\mathcal{N}(\mu,\Sigma)$, where $\Sigma$ is a dense matrix. I wish to calculate the expectation of $f(u_i)$. </p>
<p>Is $$E(f(u_i))=\int f(u_i)\mathcal{N}(u_i|\mu_i,\Sigma_{ii})\,du_i$$ If so provide a simple proof? Also does this apply to other multi... | g27842 | [
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0.005202286411076784,
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0.061823710799217224,
0.012409449554979801,
... |
<p>I'm interested in fitting a conditional Poisson regression model using PROC GENMOD in SAS to analyze a matched cohort study. However, it's not quite clear to me how I should exactly go about it. </p>
<p>My impression is that a REPEATED statement should be used along with the events/trials syntax, but if so then how... | g60062 | [
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... |
<p>I would like to know if the normal forecasting methods apply for count data, in specific a dataset that contains several zeros?</p>
<p>I have data set that counts the usage of a service on an hourly basis, and I would like to make a forecast on the hour in which the service is going to be used based on the historic... | g60063 | [
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0.009579669684171677,
-0.01071122195571661,
0.041081055998802185,
0... |
<p>An author did not report an effect size so I am hoping you might be able to help me calculate it.</p>
<p>I know the Means are:</p>
<pre><code>Condition 1: 326
Condition 2: 558
</code></pre>
<p>Sample size:</p>
<pre><code>Cond1: 11
Cond2: 12
</code></pre>
<p> </p>
<pre><code>T-test p value: .04
</code></pre> | g60064 | [
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0.05487769842147827,
-0.010308407247066498,
... |
<p>In [1], Schraudolph presents an algorithm for updating a weight $w$ and some auxiliary variables $p$ and $v$ given a vector gradient $g$ and another vector "$Cv$". The update rules attempt to make it so that v goes to $C^{-1}g$ where $C$ could be, for example, the Hessian. $Cv$ is a vector like $g$ that is passed ... | g60065 | [
0.00849223043769598,
-0.03650373965501785,
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0.009507332928478718,
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0.03839719295501709,
-0.03945457562804222,
0.06795874238014221,
0.04919097200036049,
0.064534... |
<p>Your help on the following question is appreciated. Thanks.</p>
<p>I know paired-sample t test is for the same group of people to test their pre and post tests and see if they have a significant gain between their pre and post tests. If the treatment is progressive, can I use the same people to collect data over ti... | g15972 | [
0.0026551957707852125,
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0.016868285834789276,
0.04939178377389908,
0.06025530397891998,
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-... |
<p>The title may not be entirely accurate for what I'm looking for.</p>
<p>I am measuring the growth of a database table over time in order to estimate how much disk I will need in the future. With just a single table I guess I could apply linear regression to make my estimate, getting more accurate as more measurment... | g60066 | [
-0.010560769587755203,
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-0.005960213020443916,
-0.007494625169783831,
0.01987268775701523,
0.048004359006881714,
0.03... |
<p>I read something about standard error, which tells that sample mean is not accurate estimation because we do not sample full population of size N. But, what if sample size n = N or exceeds N, i.e. n > N? Can standard error can be more accurate than the standard deviation?</p> | g60067 | [
0.014872997999191284,
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0.008275327272713184,
-0.03656741604208946,
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... |
<p>Is it possible to test a one-tailed hypothesis with Fisher's exact test for more than a 2x2 contingency table? I am asking because the online calculators I found for this case only give a 2-sided value (e.g., like this one: <a href="http://vassarstats.net/fisher2x4.html" rel="nofollow">http://vassarstats.net/fisher2... | g48221 | [
-0.0038039167411625385,
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-0.027394050732254982,
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0.02806789055466652,
0... |
<p>I have a repeated measures (time 1, time 2) experimental design and would like to run a confirmatory factor analysis on the scales I've used and to follow up with a cronbach's alpha. However I am unsure if I should run the analyses on time 1 or time 2 data. Any advise?</p> | g60068 | [
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-0.0045226686634123325,
0.0009208119590766728,
-0.0026250972878187895,
-0.02525538019835949,
... |
<p>For a prospective occupational cohort where everyone is exposed to one or more chemical agents, examining BMI at follow-up compared to a specific chemical exposure at baseline, is it necessary to control for baseline BMI? Is it better to model change in BMI or BMI at followup? There is no unexposed group -- just coh... | g492 | [
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0.016667457297444344,
0.029510553926229477,
0.013093105517327785,
... |
<p>Still working on my financial datasets, I am now trying to observe the effects of the pre-processing on the results of my study. </p>
<p>To sum it up: I have thirty time series of prices (the main indices, forex & bonds over ten years) and I want to observe markets trends. The main idea is to observe the correl... | g60069 | [
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0.021272890269756317,
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0.04741714149713516,
... |
<p>I am developing an online assessment system and I need to calibrate the bank of questions but I do not have enough people to implement a pilot test. That is why I decided to simulate the responses of the question bank. I will use the Rasch model for the development of a computer adaptive test (CAT); I have only ques... | g60070 | [
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0.0045047360472381115,
0.03222170099616051,
0.04... |
<p>Greedings to everybody.</p>
<p>I have the dataset which you can find <a href="https://dl.dropboxusercontent.com/u/8546316/Dataset.csv" rel="nofollow" title="here">here</a>, containing many different characteristics of different houses, including their types of heating, or the number of adults and children living in... | g300 | [
0.03706766664981842,
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0.03085576929152012,
0.026172291487455368,
0.05455174669623375,
0.064... |
<p><strong>Background</strong></p>
<p>I'm working on a new effort estimation model (dissertation work) which involves software engineers organizing tasks (rank ordering) in order of increasing effort based solely on their understanding of the requirements. For example, writing a function to <em>calculate an average</e... | g15975 | [
-0.03133412078022957,
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0.03537469729781151,
0.00001980630804609973,
-0.05618223920464516,
0.035560861229896545,
... |
<p>I've got a dataset that looks like this:</p>
<pre><code>id start end score1 score2
[...]
LmjF.31 280000 290000 . .
LmjF.31 290000 300000 . 2686
LmjF.31 300000 310000 . .
LmjF.31 310000 320000 . 74
LmjF.31 320000 330000 . 1897
LmjF.31 330000 340000 . 41... | g60071 | [
0.022214464843273163,
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0.04413282871246338,
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-0.027189569547772408,
0.02069392055273056,
0.05373954400420189,
0.0219182837754488,
0.02... |
<p>I think it is fair to say statistics is an applied science so when averages and standard deviations are calculated it is because someone is looking to make some decisions based on those numbers. Part of being a good statistician then I would hope is being able to "sense" when the sample data can be trusted and when ... | g44921 | [
0.06721431761980057,
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0.027218587696552277,
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-0.05888928100466728,
0.05366714298725128,
0.009568530134856701,
0.06655563414096832,
0.0... |
<p>From <a href="http://en.wikipedia.org/wiki/Partial_correlation" rel="nofollow">Wikipedia</a></p>
<blockquote>
<p>Formally, the partial correlation between $X$ and $Y$ given a set of $n$ controlling variables $Z = \{Z_1, Z_2, …, Z_n\}$, written $ρ_{XY·Z}$, is the correlation between the residuals $RX$ and $RY$ res... | g60072 | [
0.06641628593206406,
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0.029492150992155075,
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0.03737030178308487,
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-0.01176876574754715,
-0.03489821404218674,
0.01764485239982605,
-0.050186242908239365,
0.020833... |
<p>Are there any methods to correct bias in Cox proportional hazard model caused by non-randomly selected sample (something like Heckman's correction)?</p>
<p><strong>Background</strong>:<br>
Lets say the situation looks as follows:<br>
- During first two years all clients are accepted.<br>
- After those two years a C... | g60073 | [
0.0335625596344471,
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0.06854568421840668,
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0.042103078216314316,
0.054759569466114044,
0.07719366997480392,
0.05469413846731186,
0.004494... |
<p>I'm looking for advice on how to analyze complex survey data with multilevel models in R. I've used the <code>survey</code> package to weight for unequal probabilities of selection in one-level models, but this package does not have functions for multilevel modeling. The <code>lme4</code> package is great for multil... | g12522 | [
-0.029386552050709724,
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0.031174801290035248,
0.015897873789072037,
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0.058982003480196,
0.020... |
<p>For answering my research question I am interested in the correlation between the random slopes and random intercepts in a multilevel model, estimated using the R library lme4. </p>
<p>The data I have is: Y (test-scores from students), SES (socio-economic status for each student) and schoolid (ID for each school). ... | g60074 | [
0.000545554212294519,
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-0.009127010591328144,
0.015846475958824158,
-0.001211451948620379,
0.04410691559314728,
0... |
<p>I am running an experiment looking at brain volume changes in a rare disorder. We have a small number of patients (n = 8) but a large control group (n = 100). Some colleagues have suggested that a balanced group should be used, ie. selecting 8 control brains, but I find this counterintuitive.</p>
<p>Doesn't it make... | g60075 | [
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0.05181649699807167,
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0... |
<p>Say I want to perform a two-way ANOVA, and I want to use the sources A, B . For A I test at levels A1 and A2, for B at B1,B2 and B3. So when I do the analysis I regress on the dummies with, for instance, A1, B1 as base case. So I get the model
$$y = \beta_0 + x_{A2}\alpha_2 + x_{B2}\beta_2 + x_{B3}\beta_3$$
where t... | g60076 | [
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0.040909092873334885,
0.008354995399713516,
... |
<p>I have a set of data and want to know whether they fall in 1, 2 or 3 groups. </p>
<p>I started exploring the question by using k-means in MATLAB. By just looking at the distance from the centroid of each cluster by eye it looks like I might have two clusters, but I would like to be able to back this up with some st... | g60077 | [
0.00508245499804616,
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0.03790683671832085,
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0.059771060943603516,
... |
<p>I am new to the concept of thresholding a variance-covariance matrix and am having trouble understanding the exact process. I am following <a href="http://dept.stat.lsa.umich.edu/~elevina/thpaper.pdf" rel="nofollow">Bickel and Levina (2008)</a> in choosing a hard threshold. What troubles me is their equation numbe... | g60078 | [
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0.0504084974527359,
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0.01728382520377636,
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-0.... |
<p>I know that orthogonalization in LS is to avoid inverting <em>X'X</em>. The idea behind it is to find variables <em>Z</em> that are orthogonal to each other. Although the process to find those is clear to me, I don't get the way to find the coefficients.
The algorithm leaves $Z_1=X_1$ (I leave the first transformed... | g2193 | [
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0.0005951520870439708,
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-0.015655461698770523,
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0.05849616974592209,
0.019476816058158875,
0.0... |
<p>If I want to investigate how two continuous variables are linked, what is the difference between calculating the <em>correlation</em> coefficient (Pearson's r) versus calculating the (simple linear) <em>regression</em> coefficient?</p>
<p>I see people who, if the regression coefficient is significantly different fr... | g15983 | [
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0.008138182573020458,
0.006666738074272871,
-0.... |
<p>I want to predict the success of a tweet.
In my case a tweet is successful when the sum of the number of favorites and the number of retweets is greater than 5. So my outcome value y is:</p>
<p><strong>y=
if((retweets + favorites) >5 ==1</strong>
else == 0</p>
<p>Therefore I created the following dataset:
(This... | g3491 | [
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0.002690731780603528,
0.0064077433198690414,
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0.08210834115743637,
0... |
<p>I am new in this forum.</p>
<p>I am beginning to work with time series, I have a daily (25,000+ observations) temperature dataset (01/01/1946 - 07/01/2014) </p>
<p>I want to test for the following:</p>
<ol>
<li><strong>Trends:</strong> So far I used OLS, but I have heard about using
Mann-Kendall test may be usefu... | g60079 | [
0.016085699200630188,
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0.05198383703827858,
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-0.02465629205107689,
0.03410225361585617,
0.008026016876101494,
0.04954478144645691,
0.0... |
<p>Suppose we have $m$ baseline data points and $n$ post-baseline data points where $m < n$. This is for one subject. Is it possible to perform a paired t-test on this data even though $m+n$ is odd? Can we thrown away the data that is not paired and perform the test?</p>
<p>For example, suppose the baseline data is... | g60080 | [
0.04153738543391228,
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0.004371532704681158,
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0.002768669044598937,
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0.0347478874027729,
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0... |
<p>How do I define generators in Minitab 16?</p>
<p>I have an experiment design (DOE) with 5 factors and 2 generators.</p>
<p>I entered D=ABC E=AC in the box of generators but it says only F through G ? </p> | g60081 | [
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0.02576238475739956,
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0.025080041959881783,
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0.05331295728683472,
-0... |
<p>If I have 10 classification accuracies for 3 different parameter, and I perform an ANOVA test which yields $F=1.19$ and $\text{Prob>F}$ $0.3201$. The parameter value indicates the number of features. Does that mean none of the 3 parameter values yields a significantly different result than the other? </p>
<p>Mo... | g60082 | [
0.04669182747602463,
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0.01067560724914074,
0.026407692581415176,
0.07750069350004196,
0.014933522790670395,
0.012807467952370644,
0.0427003875374794,
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0.02248045988380909,
-0.01986042782664299,
0.015463858842849731,
0.03402424603700638,
0.043150622... |
<p>I'm wondering about the monotonic quantile transformation in case of a t distribution. First, for explanation, lets consider a normal distribution:</p>
<p>\begin{align*}
f(l | \mu , \sigma ^2)=\frac{1}{\sigma \sqrt{2 \pi}} e^{-\frac{(l-\mu)^2}{2 \sigma ^2}}
\end{align*}</p>
<p>A quantile at $\alpha$ can be calcula... | g60083 | [
0.01530137937515974,
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0.004031764343380928,
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0.049748022109270096,
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0.031923383474349976,
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0.025220448151230812,
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0.02449856884777546,
0.04130842536687851,
-0.02... |
<p>I have 3 variables. Income is the dependent variable(continuous), sex(binomial), workhrs(categorical) i fitted a linear model and obtained the result:</p>
<p>My question is: Is this model usable? The NA values come from the fact that workhrs is missing 4 categories. The fifth one is i think due to coliniarity.
The ... | g60084 | [
-0.027825167402625084,
-0.020176080986857414,
0.01871080882847309,
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0.05582362785935402,
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0.043204840272665024,
-0.06585866212844849,
-0.0006966219516471028,
0.03810717910528183,
... |
<p>I've read that the area under the ROC curve is equivalent to a Mann-Whitney U-score. Is a multiclass AUC score (which averages the AUC scores for pairs of classes) related to the Kruskal-Wallis test statistic?</p> | g452 | [
-0.01187472976744175,
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0.02000609040260315,
0.07655090093612671,
0.... |
<p>I'm throwing here the problem as I received it.</p>
<p>I have two random variables. One of which is <strong>continuous</strong> (Y) and the other one which is discrete <strong>ordinal</strong> (X). I put below the plot I received together with the query.</p>
<p><img src="http://i.stack.imgur.com/bidGa.png" alt="en... | g15994 | [
0.014224536716938019,
-0.01549533847719431,
-0.016057198867201805,
-0.07618776708841324,
-0.018110059201717377,
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0.008121316321194172,
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-0.024188602343201637,
0.05473169684410095,
0.002964602317661047,
0.008091695606708527,
... |
<p>I need to understand what <code>mvpart</code> is doing. Which index does it use as a splitting criterion (in my case, method=class)? Does it use simultaneous partitioning along multiple axis (multivariate)? Are there any references I can read on the subject?</p> | g60085 | [
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0.018232297152280807,
0.005971360020339489,
-0.0015583293279632926,
0.027271172031760216,
0.041592326015233994,... |
<p>I usually make calculations of the estimated profitability of some businesses. These calculations are function of some parameters: estimated prices, estimated demand, estimated exchange rates, ...</p>
<p>I often assume that all of these input parameters are normally distributed, and I assess their means and standar... | g60086 | [
0.01987953670322895,
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0.0178239569067955,
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-0.025923073291778564,
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0.02931438758969307,
0.020340435206890106,
0.0... |
<p>I´ve been researching about automatic determination of parameters for DBSCAN (a density-based clustering algorithm -- <a href="http://en.wikipedia.org/wiki/DBSCAN" rel="nofollow">http://en.wikipedia.org/wiki/DBSCAN</a>), especially <em>eps</em>, and have found the following paper, which proposes a method for determi... | g60087 | [
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-0.022935155779123306,
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0.006467675790190697,
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0.0010221698321402073,
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0.06601538509130478,... |
<p>I applied OLS on a regression model that looks as follows:
$$
y = b_0 + b_1x_1 + b_2x_2
$$
and found that signs of heteroscedasticity. In an econometrics text book, I found that I can divide each variable by the square root of an independent variable. So the new model looks as follows:
$$
\frac{y}{\sqrt{x_1}} = \fra... | g60088 | [
-0.006886910181492567,
-0.016976766288280487,
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0.052925292402505875,
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0.021716337651014328,
0.05045543238520622,
0.019708700478076935,
... |
<p>I had set of binary variables. To apply logistic regression, I have checked association between dependent and independent variables and considered only those independent variables in the model which came to be associated with dependent variable.
My query is whether it is an appropriate way of fitting logistic regres... | g60089 | [
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0.0231315940618515,
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0.06689126789569855,
0.043722592294216156,
0.021886790171265602,
0.0... |
<p>I use KNN regression to train out a model. The model estimates running time of a program based on different inputs, and the output is a single variable, which is time (double type).</p>
<p>I want to evaluate this model. I have a list of observation times and a list of prediction times. I would like to know how I ca... | g60090 | [
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0.005241046659648418,
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0.02303297258913517,
0.043516915291547775,
0... |
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