Statistical Analysis Stack Exchange
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1500 questions
87
votes
5 answers

Cross-Validation in plain english?

How would you describe cross-validation to someone without a data analysis background?
Shane
  • 12,461
87
votes
3 answers

When to use generalized estimating equations vs. mixed effects models?

I have been quite happily using mixed effects models for a while now with longitudinal data. I wish I could fit AR relationships in lmer (I think I'm right that I can't do this?) but I don't think it's desperately important so I don't worry too…
Chris Beeley
  • 5,761
87
votes
1 answer

How to interpret coefficients in a Poisson regression?

How can I interpret the main effects (coefficients for dummy-coded factor) in a Poisson regression? Assume the following example: treatment <- factor(rep(c(1, 2), c(43, 41)), levels = c(1, 2), …
user734124
87
votes
7 answers

Is it meaningful to calculate Pearson or Spearman correlation between two Boolean vectors?

There are two Boolean vectors, which contain 0 and 1 only. If I calculate the Pearson or Spearman correlation, are they meaningful or reasonable?
Zhilong Jia
  • 1,045
87
votes
7 answers

Rules of thumb for minimum sample size for multiple regression

Within the context of a research proposal in the social sciences, I was asked the following question: I have always gone by 100 + m (where m is the number of predictors) when determining minimum sample size for multiple regression. Is…
Jeromy Anglim
  • 44,984
86
votes
10 answers

Regarding p-values, why 1% and 5%? Why not 6% or 10%?

Regarding p-values, I am wondering why $1$% and $5$% seem to be the gold standard for "statistical significance". Why not other values, like $6$% or $10$%? Is there a fundamental mathematical reason for this, or is this just a widely held…
Contango
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86
votes
7 answers

Line of best fit does not look like a good fit. Why?

Have a look at this Excel graph: The 'common sense' line-of-best-fit would appear be an almost vertical line straight through the center of the points (edited by hand in red). However the linear trend line as decided by Excel is the diagonal black…
ConanTheGerbil
  • 931
86
votes
4 answers

Reduce Classification Probability Threshold

I have a question regarding classification in general. Let $f$ be a classifier, which outputs a set of probabilities given some data D. Normally, one would say: well, if $P(c|D) > 0.5$, we will assign a class 1, otherwise 0 (let this be a binary…
sdgaw erzswer
  • 1,409
86
votes
7 answers

Using principal component analysis (PCA) for feature selection

I'm new to feature selection and I was wondering how you would use PCA to perform feature selection. Does PCA compute a relative score for each input variable that you can use to filter out noninformative input variables? Basically, I want to be…
Michael
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86
votes
2 answers

Bayes regression: how is it done in comparison to standard regression?

I got some questions about the Bayesian regression: Given a standard regression as $y = \beta_0 + \beta_1 x + \varepsilon$. If I want to change this into a Bayesian regression, do I need prior distributions both for $\beta_0$ and $\beta_1$ (or…
TinglTanglBob
  • 1,056
86
votes
5 answers

What is translation invariance in computer vision and convolutional neural network?

I don't have computer vision background, yet when I read some image processing and convolutional neural networks related articles and papers, I constantly face the term, translation invariance, or translation invariant. Or I read alot that the…
Hossein
  • 2,385
86
votes
5 answers

Please explain the waiting paradox

A few years ago I designed a radiation detector that works by measuring the interval between events rather than counting them. My assumption was, that when measuring non-contiguous samples, on average I would measure half of the actual interval.…
Stephen Sackett
  • 963
86
votes
5 answers

How exactly did statisticians agree to using (n-1) as the unbiased estimator for population variance without simulation?

The formula for computing variance has $(n-1)$ in the denominator: $s^2 = \frac{\sum_{i=1}^N (x_i - \bar{x})^2}{n-1}$ I've always wondered why. However, reading and watching a few good videos about "why" it is, it seems, $(n-1)$ is a good unbiased…
PhD
  • 14,627
85
votes
13 answers

Famous statistical wins and horror stories for teaching purposes

I am designing a one year program in data analysis with a local community college. The program aims to prepare students to handle basic tasks in data analysis, visualization and summarization, advanced Excel skills and R programming. I would like…
Placidia
  • 14,361
85
votes
2 answers

How does a simple logistic regression model achieve a 92% classification accuracy on MNIST?

Even though all the images in the MNIST dataset are centered, with a similar scale, and face up with no rotations, they have a significant handwriting variation that puzzles me how a linear model achieves such a high classification accuracy. As far…
Nitish Agarwal
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