# All Questions

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### finding Limiting distribution $\displaystyle\frac{\sum_{i=1}^n X_i}{\sum_{i=1}^n Y_i}$

let $X_1,X_2,\ldots,X_n$ are random sample of bernoulli distribution with parameter of $\displaystyle\frac{\theta_1}{\theta_1+\theta_2}$ and $Y_1,Y_2,\ldots,Y_n$ are random sample of geometric ...
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### Multi-armed bandit algorithms vs Uplift modeling

Multi-Armed Bandit: http://en.wikipedia.org/wiki/Multi-armed_bandit Uplift Modeling: http://en.wikipedia.org/wiki/Uplift_modelling How are these two approaches different? How are they similar? Is ...
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### How to interpret output of poisson.test?

Chapter 11 of Introduction to Data Science is about Poisson distributions. One example sample has 58638 observations out of 100000 with a value less than or equal to 10. ...
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### Forecasting irregular time series (with R)

There are several methods to make forecasts of equidistant time series (e.g. Holt-Winters, ARIMA, ...). However I am currently working on the following irregular spaced data set, which has a varying ...
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### Kolmogorov-Smirnov with parameter estimates

Can someone explain in as clear a (formalish mathematical) way as possible why the KS test in original form with parameter estimates is unreliable?
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### In left skewed data, what is the relationship between mean and median?

I found this question on the open MOOC from Stanford, however the answer is not present. I think the median $\leq$ mean. Is this the case?
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### Need subspace partition algorithm, not necessarily a full classifier

The image above represents a hypothetical data set of interest. For some set of points in N-dimensional space (each attribute of the data set corresponds to one dimension), I want to identify ...
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### Optimal weighting matrix instrumental variables estimator

The formula for the optimal weighting matrix when you perform regression with more instrumental variables than endogenous predictors is the following: $W_{opt} = (\frac{1}{N}Z'Z)^{-1}$ This tells ...
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### Do I have to learn SAS if I want to go into industry?

I am currently a PhD student in Biostatistics (finishing my 2nd year). My original goal when entering graduate school was to go into academia. Recently I have been debating this choice and wondering ...
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### Variance of Z for Z = X + Y, when X and Y correlated

So I'm trying to show that ${\rm Var}(Z) \le 2({\rm Var}(X)+{\rm Var}(Y))$ for $Z = X + Y$. This seems to be pretty easy to show given that $X$ and $Y$ are uncorrelated. But I'm running into trouble ...
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### Using MANOVA for classification without separating training and test sets

In this study: Rosenblum, Sara, et al. "Handwriting as an objective tool for Parkinson’s disease diagnosis." Journal of neurology 260.9 (2013): 2357-2361 The researchers attempt to classify ...
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### Statistic test on percentage correct classified by emotion recognition

For a potential emotion recognition bachelor-project I was wondering what statistical test I have to perform when I get my results to test whether it's significant. I will be testing which combination ...
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### AIC BIC Mallows Cp Cross Validation Model Selection

If you have several linear models, say model1, model2 and model3, how would you cross-validate it to pick the best model? (In R) I'm wondering this because my AIC and BIC for each model are not ...
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### Difference between iid data and non-iid data for a simple regression problem

I am trying to understand the difference between iid and non-iid data. Let's consider a given time series, and say it's reasonable to assume that at each time point the random variable $X_t$ depends ...
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### R: One period our cross validation with time series

I have quarterly data with one causal variable (X) and one dependent variable (Y). 30 such observations. I have the X variable for a quarter, and I'm seeking to predict that quarter's Y. The ...