# All Questions

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### Implementing random forest to predict the success rate and time of comletion

I have a huge dataset with more than 120 columns for which i'm trying to classify whether the order will be succesful or not. There are two parameters which i need figure out. One is the probability ...
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### How to analyze my repeated measures data?

I have data on 200 subjects with baseline data and follow-up data after 1 and 2 years. The dependent variable is nominal: whether each subject lives at home, has passed away or lives in an institution ...
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### What happens when there's a one-tailed hypothesis test and the results are in the other tail?

For example, let's say I'm using a one-tailed t-test to see if a box of Lucky Charms cereal has more than 100 marshmallows. I know the consequences of using a one-tailed t-test and how it wouldn't be ...
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### How to turn nlme syntax into manuscript appropriate equation?

I ran an linear mixed-effects analysis in R using the nlme package. I would like to write out the algebraic equation of the model's specifications. Unfortunately, I do not know exactly how to ...
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### Outliers detection for clustering methods

I'm in the middle of a result analysis for some clustering methods, doing quality tests for different clustering outputs coming from an singular input dataset where data preprocessing and cleaning ...
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### How to run repeated-measures ANOVA when data points per subject vary?

I am attempting to run statistics in the following scenario: I have a list of hospital visits by approx. 60 patients to the emergency room. Each patient gets an EKG done of their heart, and I have ...
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### predicting the percentile of response variable via linear regression of zscores

Sometimes during modeling we are faced with non-normal data. One of the presumptions of linear regression is the response data being normal. I wish I found a better example data set to illustrate ...
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### High autocorrelation parameters? [on hold]

I plotted the autocorrelation and partial autocorrelation for two of my time series data in R. But it seems that one of the autocorrelation plots of the two has much higher autocorrelation parameters ...
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### Minimum Detectable Effect Sampling Weight

An experiment has two sub-populations, A and B, and I want to estimate a pooled intention to treat (ITT) effect $$Y_{i}=\beta_0 + \beta_1 T_i + \epsilon_i$$ where $T_i=1$ if treated in either ...
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### Error propagation over percentile confidence intervals for bootstrapped regression coefficients

I apologize if this is extremely simple or I'm going about this the wrong way or it has been asked before. Please point me in the right direction if so as I might just be searching the wrong question. ...
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### Permutation test for F statistics in the OLS setting

Can anyone explain to me that what is the point of performing a permutation test? For example, in the OLS analysis, we fit $X\beta$ to $Y_i$,for the permutation test, we let $\tau$ be a permutation ...
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### Introductory graduate-level survey sampling textbook?

I've already seen this. For someone who has a mathematical mindset and is starting a graduate program in stats, what is a good text on survey sampling? If it comes with R code samples, that would be ...
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### Categorical Vs Ordered factors as independent variables in logistic regression & random forest in R? [on hold]

I am a newbie, just started learning predictive modeling through R. Could anyone please explain if there will be any difference in the modeling if we change the ordinal factors to categorical factors ...
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### Would using the md5 for treatment assignment introduce any biases?

Disclaimer: I'm not sure if there's a better stackexchange for this, but since I consider experimental design an integral part of causal/statistical inference, I'm hoping this is an appropriate ...
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### Contrasts / Post Hoc Tests for three way repeated measures ANOVA

I have three factors A B and C with 2, 2 and 3 levels. A and C have significant main effects, B is not significant, interaction A*C is significant, the others are not. Now I want to know how to ...
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### In R, what does qqnorm actually do?

qqnorm(x) plot(qnorm(seq(80)/81),sort(x)) Finding that the plots produced by the commands above are slightly different from each other, I tried this: ...
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### Fail to improve recall in classification

I have a large data set with over 700,000 examples and I tried to (binary) classify the data set with Naive Bayes and Random Forest. The task was carried out in Python and Scikit-learn data The data ...
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### Does a high autocorrelation imply high predictability using an AR model?

Assuming that I have a list of time-series which all have significant autocorrelation at lag 1 and no significant autocorrelation at any other lags. So if I want to test for the predictive abilities ...
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### Data sets for which PCA can classify better than LDA (using a very small training set)

Can you provide an example of a dataset where PCA can find better discriminant directions than (LDA) Linear Discriminant Analysis? One example is UCI's wine data set. If you use only 2 observations ...
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### Power Analysis Weighted Data

Suppose an outcome depends on the intensity of a treatment intervention $\pi$, where $\pi \in [0,1]$. Given intensity of treatment $\pi$, the data generating process is Y_i = \beta_0 + \beta_1 \pi ...
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### Why is the derivative not zero?

I am working with survival models and I am using R's coxph function to learn the Cox proportional hazard model. To try it out, I am using the standard veteran dataset (obtainable by loading the ...
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### Evaluating a proportion over time

How do I evaluate a proportion within a population over time? For example, a group of patients undergoes an intervention. Assessment of knowledge is obtained pre-intervention and post-intervention, ...
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### Question on Residuals

After generating the regression model in R using lm, the results will be passed to summary function. results <- lm(y~x, data) summary(results) This function ...
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### How is it possible to have a significant correlation between two variables but a low covariance?

How is it possible to have a significant correlation between two variables but a low covariance? What does this mean?
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### Help with Data Analysis - using Minitab

I am new to DOE. I have performed manufacturing conditions optimization experiment (turning). I have 4 controllable input parameters and 2 response variables From my experimental data I have 4 ...
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### Effect of “parameters.to.save” in R2jags/ JAGS

I'm using the package R2jags in R, which uses the parameters.to.save argument to specify parameters. I'm interested in the statistical distinction between a ...
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### PCA on count-based data

I'm looking to do a PCA analysis on count based data itself rather than averages. I'm hoping this will help for variable observation depths; for example, 3/4 reads is not really equivalent to 15/20. ...
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### Named entity resolution overfitting

I am using Maximum entropy algo (from apache opennlp package) for training named entity resoltion model. I am using default features set: token bi-gram and some token classifiers like isUpperCase ...
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### assigning values to range of scores in spss [on hold]

I have to use z-scores of final exam percentages to classify students as high (z-score > 1 ) vs. low performing (z-score < 1) for further analyses. Is there a way this could be done in spss ...
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### Restarting Lag based on Change in Name in Different Column [migrated]

I am trying to insert lags of a variable into a separate column in my data frame on R. However, I want the lags to 'restart' every time the name in a different column changes. An example of data is ...
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### Why log-transforming the data before performing principal component analysis?

Im following a tutorial here: http://www.r-bloggers.com/computing-and-visualizing-pca-in-r/ to gain a better understanding of PCA. The tutorial uses the Iris dataset and applies a log transform prior ...
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### Density forecasting

I am having some troubles obtaining density forecasts of any returns series. As I couldn't find any numerical examples on the Internet, I would like to ask you guys for some help. My goal is to ...
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### Use of PERMANOVA [on hold]

I'm struggling with a problem. Can I use PERMANOVA to find differences in abundace of a single specie, between years and between river sections? And how do I do those matrix in order to use them in ...
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### bias-variance decomposition and independence of $X$ and $\epsilon$

I took a look at a couple of derivations of this decomposition and I think they all require that $E[\epsilon \hat{f}] = 0$. The most transparent one I found was from Wikipedia here. I reproduce the ...
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### Pearsons Chi Squared and z-scores question

1) I have a list of who is short or not in a group(by using binary 0,1).I also have a list of where each case is located in region. If I do crosstabs for the calculate the percentage of short(1) in ...
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### Calculating Standard Error of Standard Deviation

Following this post , I think first I need to be theoretically sound . In my theory class , I learnt that inverse of information matrix is the variance-covariance matrix of estimates . To find the ...
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### Linear Regression, $\beta$, Correlation Coefficient, Spherical Distribution

In a linear regression $y = \alpha + \beta x + \epsilon$ where $\epsilon \sim N(0,\sigma)$ $\beta = r_{XY} \frac{\sigma_Y}{\sigma_X}$ The equation is sensical when (X,Y) follows a multivariate ...
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### What is VectorSource and VCorpus in 'tm' (Text Mining) package in R

I'm not quite sure what exactly VectorSource and VCorpus are in 'tm' package. The documentation is unclear on these, can anyone make me understand in simple terms?
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### I have a hierarchical bayesian logit model with large variation in outcome between units. Should I still use a hierarchical model?

So instead of using country and time fixed effects for a time series cross section data on country-years with a binary outcome, I'm using a hierarchical logit model with country and time random ...
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### Feature Normalization & Learning

I'm working on a cell classifier (as in Biological Cells) using images obtained by microscope. Right now I have about 12 Features written (color,width-height ratio, shape, couple of texture features, ...
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### Permanent and temporary shock income, variance decomposition

I have a balanced panel data (N= 190, T=5). It's about income and personal characteristics of the householder. I would like to find the coefficients of a temporary and of a permanent income shock. I ...
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### Meta Analysis for one proportion

I have data summarizing proportion of events from 5 different papers. The proportions are in %'s. For example, in paper number 1, there was a report of 2000 people and a proportion of 10%. I want a ...
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### Simulating exponential distribution for insertion events

Similar to the this question: Understanding the mean and rate of an exponential distribution ; I would like to know how the answer provided there, has to be modified so it reflects a Poisson process. ...
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### Non-parametric alternative to a mixed anova?

My data fails assumptions of variance - (norm dist is good though) - and I was wondering if anyone had a suggestion for an alternative to a mixed anova? Three repeated measures (Test 1, Test 2, Test ...
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### Model selection for linear regression with categorical variables

I regressed the dependent variable Rating (numeric) on Judge which is categorical. The output of the first model is given at the end of the question. Only Judge John Foy and Linda Murphy came out to ...
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### explaining LARS algorithm in a simple way

I am thinking to write a LARS algorithm that uses different optimizations in each step. Can somebody briefly explain Least angel regression, LARS (see here) to me? then I will try to write my own LARS ...
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### how to model and implement bayesian change point with longitudinal data

I am working on Bayesian change point of Poisson data with different identities that is longitudinal. I have understood to degree the hierarchical structure of the posterior with hyper priors for data ...
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### Model selection for linear regression with categorical variables

I regressed the dependent variable Rating (numeric) on Judge which is categorical. The output of the first model is given at the ...
Let the time (in hours) needed to repair a broken car be a continuous random variable $X$. Then, in the case of $a$ and $b$ being two positive numbers and $b$ > $a$, would the following two problems ...