Most Popular
1500 questions
35
votes
3 answers
Why could centering independent variables change the main effects with moderation?
I have a question related to multiple regression and interaction, inspired by this CV thread: Interaction term using centered variables hierarchical regression analysis? What variables should we center?
When checking for a moderation effect I do…
Marc Schubert
- 351
- 1
- 4
- 3
35
votes
6 answers
How do I calculate a weighted standard deviation? In Excel?
So, I have a data set of percentages like so:
100 / 10000 = 1% (0.01)
2 / 5 = 40% (0.4)
4 / 3 = 133% (1.3)
1000 / 2000 = 50% (0.5)
I want to find the standard deviation of the percentages, but weighted for their…
Yahel
- 555
35
votes
1 answer
Negative binomial regression question - is it a poor model?
I am reading a very interesting article by Sellers and Shmueli on regression models for count data. Near the beginning (p. 944) they cite McCullaugh and Nelder (1989) saying that negative binomial regression is unpopular and has a problematic…
Peter Flom
- 119,535
- 36
- 175
- 383
35
votes
2 answers
Likelihood ratio test in R
Suppose I am going to do a univariate logistic regression on several independent variables, like this:
mod.a <- glm(x ~ a, data=z, family=binominal("logistic"))
mod.b <- glm(x ~ b, data=z, family=binominal("logistic"))
I did a model comparison…
lokheart
- 3,199
- 9
- 40
- 49
35
votes
2 answers
lme and lmer comparison
I was wondering if anyone could enlighten me on the current differences between these two functions. I found the following question: How to choose nlme or lme4 R library for mixed effects models?, but that dates from a couple of years ago. That's a…
Hong Ooi
- 8,249
35
votes
4 answers
Why are lower p-values not more evidence against the null? Arguments from Johansson 2011
Johansson (2011) in "Hail the impossible: p-values, evidence, and likelihood" (here is also link to the journal) states that lower $p$-values are often considered as stronger evidence against the null. Johansson implies that people would consider…
luciano
- 14,269
35
votes
3 answers
Visualizing the intersections of many sets
Is there a visualization model that is good for showing the intersection overlap of many sets?
I am thinking something like Venn diagrams but that somehow might lend itself better to a larger number of sets such as 10 or more. Wikipedia does show…
Kyle Brandt
- 767
35
votes
3 answers
Why is the formula for standard error the way it is?
So just "why" is $SE = \frac{s}{\sqrt n}$ ? How should one interpret/articulate the reason of having $\sqrt n$ in the denominator. Why do we divide sample mean by the square root of the sample size, intuitively speaking? And how/why is it called…
PhD
- 14,627
35
votes
3 answers
What distribution does my data follow?
Let us say that I have 1000 components and I have been collecting data on how many times these log a failure and each time they logged a failure, I am also keeping track of how long it took my team to fix the problem. In short, I have been recording…
Legend
- 4,532
35
votes
5 answers
Can I trust ANOVA results for a non-normally distributed DV?
I have analyzed an experiment with a repeated measures ANOVA. The ANOVA is a 3x2x2x2x3 with 2 between-subject factors and 3 within (N = 189). Error rate is the dependent variable. The distribution of error rates has a skew of 3.64 and a kurtosis of…
Matt
- 741
35
votes
1 answer
Why do we do matching for causal inference vs regressing on confounders?
I'm new to the area of causal inference. From what I understand, one of the main concerns that causal inference tries to address is the effect of confounders!
For the sake of reference, let's denote the feature that we are interested in (a.k.a…
Ehsan Sh
- 515
- 5
- 7
35
votes
3 answers
Student t as mixture of gaussian
Using the student t-distribution with $k > 0$ degrees of freedom, location parameter $l$ and scale parameter $s$ having density
$$\frac{\Gamma \left(\frac{k+1}{2}\right)}{\Gamma\left(\frac{k}{2}\sqrt{k \pi s^2}\right)} \left\{ 1 + k^{-1}\left(…
Salih Ucan
- 535
35
votes
3 answers
What is the difference between EM and Gradient Ascent?
What is the difference between the algorithms EM (Expectation Maximization) and Gradient Ascent (or descent)? Is there any condition under which they are equivalent?
Aslan986
- 756
35
votes
3 answers
In caret what is the real difference between cv and repeatedcv?
This is similar to question Caret re-sampling methods, although that really never answered this part of the question in an agreed upon way.
caret's train function offers cv and repeatedcv. What is the difference in say…
Brian Feeny
- 511
35
votes
6 answers
What is the difference between logistic regression and neural networks?
How do we explain the difference between logistic regression and neural network to an audience that have no background in statistics?
user16789
- 796