# All Questions

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### Mulitivariable regression?

For my research project on the effect of a specific kind of surgery on clinical outcome, I want to study the correlation between the improvement in clinical outcome scores (ie the difference between ...
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### Log transformation for logistic regression

Is it necessary to log transform non-normally distributed variables to perform logistic regression? If so, when is it appropriate?
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### Fit and evaluate a second order transition matrix (Markov Process) in R?

I already built one first order discrete state Markov Chain model. It was built with R using the function 'markovchainFit()' in ...
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### mixed models: wrong random intercepts and interpretation issues

I have a dataset of individues that participated in several races, but not all individuals did every race. Of every indivual I have their average speed. My goal is to have a measure of how difficult ...
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### Multiple logistic regression models and survey data

I have a set of survey data that consists of answers to 10 knowledge questions along with demographic information about the respondent. Our question of interest is to identify which demographics are ...
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### Gradient boosting algorithm (steps) question

So, far I have read following regarding boosting: Boosting is an ensemble technique. Train learner sequentially, where early learners fit simple models to the data. Analyze data for errors, that ...
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### Intercept, deterministic and stochastic cointegration

I have reading on the Johansen co integration model. I am using the jci test function of MATLAB. I have some a little trouble selecting the 'model.' can somebody explain in layman terms which and what ...
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### Efficient/fast Mahalanobis distance computation

Suppose I have $n$ data points $x_1,\dots,x_n$, each of which is $p$-dimensional. Let $\Sigma$ be the (non-singular) population covariance of these samples. With respect to $\Sigma$, what is the most ...
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### Random Forests overfitting/unbalanced classes?

Suppose I am using random forests where the classes are highly unbalanced. How do you detect over fitting and what can you do to avoid it? Breiman says in his paper that random forests do not overfit, ...
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### Duplicate AICc values for multiple models with interactions

I am going through a model selection process with a mixed-model with 3 variables: A, B, and C. B and C are orthogonal factors. B or C may interact with A, so my full model would be: fixed: ...
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### How to change the null hypothesis of the coefficient in the least squares fitting?

I have a least square fitting like this: fit = lsfit(log10(M), log10(RS), wt) This function lists statistics and p-values for the coefficient considering the ...
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### markov chain simulation [on hold]

I keep getting the error when I try to run this simulation could somebody tell me what I'm possibly doing wrong? ...
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### ETS() function, how to avoid forecast not in line with historical data?

I am working on an alogorithm in R to automatize a monthly forecast calculation. I am using, among others, the ets() function from the forecast package to calculate forecast. It is working very well. ...
376 views

### Can I use all pairwise comparisons at a factor level to perform correlation analysis?

I have 4 data sets, each with thousands of records/instances. There are 2 factors. One factor has 3 instances at each factor level (there are thousands of levels in the data set). The other factor ...
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### Correction for multiple comparisons repeated measures MANOVA [on hold]

I am running a repeated measures MANOVA and wanted to know the best way to correct for multiple comparisons. If I use Bonferroni, for example, how would I go about doing that within SPSS?
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### Bayesian Probabilistic Matrix Factorization (BPMF) with PyMC3: PositiveDefiniteError using NUTS

I've implemented the Bayesian Probabilistic Matrix Factorization algorithm using pymc3 in Python. I also implemented it's precursor, Probabilistic Matrix ...
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### Class weights in unbalanced SVM classification

The answer to this question says that class weights for unbalanced SVM classification can be picked so that that sums of the weights for each class are equal. Should this be done before ...
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### I observed very different feature scoring from two different classifiers. What does it really mean?

Here what I've done. Given the dataset, I run a Random Forests and Logistic Regression with 5 Fold Stratified Data Sampling. Then I plot the feature importance for Random Forests and Logistic ...
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### How to analyze time series with multiple readings per unit time

I have data as follows: ...
819 views

### Interpreting odds ratios less than 1 with 3-category outcome

I have a 3-category ordered outcome (food consumption: 1=no food, 2=less food, 3=more food) and a 3-category ordered predictor (food exposure: 3=no time, 2= less time, 1= more time- whereby 3=no time ...
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### Finding multiple records of the same person when the name cannot be trusted

I have a list of 100 of events, and each event has a list of thousands of persons. Some persons went to multiple events, and I would like to select all the events a person went to. I could just look ...
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### How to interpret these acf and pacf plots

Following are acf and pacf plots of a monthly data series. The second plot is acf with ci.type='ma': The persistence of high values in acf plot probably represent a long term positive trend. The ...
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### Introductory data trend analysis with R [on hold]

I am new to the data analysis world and am struggling to find relevant articles / examples related to what I'm trying to do. I have a data set that is like this, for example how many apples are sold ...
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### Can you show that $\bar{X}$ is a consistent estimator for $\lambda$ using Tchebysheff's inequality?

This question was taken from a practice exam in my statistics course. Given a random sample $X_1, X_2, ... X_n$ from a Poisson distribution with mean $\lambda$, can you show that $\bar{X}$ is ...
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### Sandwich Estimator in Maximum Likelihood Estimation of Logit

I am estimating a discrete choice model using mixed logit using Halton Draws. So everything is basically numerically done. The code is written in MATLAB. I am using MATLAB's fminunc to do ...