# All Questions

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### Logistic regression [on hold]

I'm currently suffering trying to understand statistics in class. Hopefully someone can clarify and explain in layman's language some things that I don't understand, especially relative to logistic ...
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### data prediction by regression or better ways

I am working on data prediction. Given data of a random variable $X$ and $Y$, find out how to predict $Y$ from $X$. I know how to do it by linear regression, $\hat{Y} = kX + b$. But, here, $X$ is ...
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### lagged covariate or time series for analyzing change over time in Hgb (limited observations) in the prediction of disease status

I want to test whether changes in Hemoglobin (Hgb) levels over time can help diagnose Myelodysplastic syndrome (MDS). I have a cohort of thousands of patients. Each patient has several Hgb ...
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### Minimum observations for creating dummy variables from a categorical group variable

I have an OLS regression with around 1000 observations and created a dummy variable for at least 15 different categories (catholic, muslim, hindu etc). One of the created dummy variables (spiritual) ...
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### Time Series Forecasting Method to use both Predicted and Predictor variables

I am learning Predictive modeling and building a Forecasting model to predict Insurance sales in US as a part of my academic project. I want to do Time Series forecasting. I have Y(t) as my response ...
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### Sample/Null Value

I was running through question section on my stat book and the following question was posed: If our sample value is close to the null/population value, we conclude that ... I don't get if that ...
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### What are some differences between confirmatory analysis and exploratory analysis?

In confirmatory analysis do you basically just test hypotheses? Then in exploratory analysis you try to generate hypotheses? In general, I know that you can first do exploratory analysis to form ...
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### Using all of the data

Suppose that we have data on 1000 people. Each of these people are either from California, Texas, or Hawaii. We have various lifestyle variables on each person (e.g. age, gender, etc.). We are ...
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### How to test for statistically significant differences between parameters for sigmoids fit to two different data sets?

I have two sets of data collected from two groups (group 1 in red, group 2 in blue). Each data set has been fit with a sigmoid with 4 parameters: Bottom Plateau, Top Plateau, Point of Inflection, and ...
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### qqPlot with Two Outliers

If I have a QQ plot with two extreme outliers (picture below) how should I interpret it? Do I drop the outliers? Can I treat it as normal?
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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?
313 views

### 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 ...
573 views

### 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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### Categorize continuous data effectively (taking into account a response variable)

I wonder what are the better approaches to categorize continuous data (e.g. age) than dividing them with the use of quantiles and cut function (in ...
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### What is the null hypothesis in the definition of Sensitivity and Specificity?

I have hard time to understand that what is the null hypothesis in the definition of Sensitivity and Specificity here? I'm student of Statistics and from my little knowledge in this field I can see ...
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### Analysing grade distributions: difference in proportions across years

I have data on grades obtained in a course over three consecutive years. The grade distribution includes the number of students who received a fail, pass, credit, distinction and high distinction. I ...
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