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1500 questions
66
votes
1 answer
40,000 neuroscience papers might be wrong
I saw this article in the Economist about a seemingly devastating paper [1] casting doubt on "something like 40,000 published [fMRI] studies." The error, they say, is because of "erroneous statistical assumptions." I read the paper and see it's…
R Greg Stacey
- 2,302
66
votes
7 answers
How much to pay? A practical problem
This is not a home work question but real problem faced by our company.
Very recently (2 days ago) we ordered for manufacturing of 10000 product labels to a dealer. Dealer is independent person. He gets the labels manufactured from outside and…
Neeraj
- 2,320
66
votes
18 answers
Recommended books on experiment design?
What are the panel's recommendations for books on design of experiments?
Ideally, books should be still in print or available electronically, although that may not always be feasible. If you feel moved to add a few words on what's so good about the…
walkytalky
- 1,898
66
votes
5 answers
Correlations between continuous and categorical (nominal) variables
I would like to find the correlation between a continuous (dependent variable) and a categorical (nominal: gender, independent variable) variable. Continuous data is not normally distributed. Before, I had computed it using the Spearman's $\rho$.…
65
votes
8 answers
How can a distribution have infinite mean and variance?
It would be appreciated if the following examples could be given:
A distribution with infinite mean and infinite variance.
A distribution with infinite mean and finite variance.
A distribution with finite mean and infinite variance.
A distribution…
user1205901 - Слава Україні
- 12,873
65
votes
3 answers
Explain the xkcd jelly bean comic: What makes it funny?
I see that one time out of the twenty total tests they run, $p < 0.05$, so they wrongly assume that during one of the twenty tests, the result is significant ($0.05 = 1/20$).
xkcd jelly bean comic - "Significant"
Title: Significant
Hover text:…
DJG
- 713
65
votes
7 answers
How do I test that two continuous variables are independent?
Suppose I have a sample $(X_n,Y_n), n=1..N$ from the joint distribution of $X$ and $Y$. How do I test the hypothesis that $X$ and $Y$ are independent?
No assumption is made on the joint or marginal distribution laws of $X$ and $Y$ (least of all…
sds
- 2,236
65
votes
11 answers
How can I determine which of two sequences of coin flips is real and which is fake?
This is an interesting problem I came across. I'm attempting to write a Python program to get a solution to it; however, I'm not sure how to proceed. So far, I know that I would expect the counts of heads to follow a binomial, and length of runs (of…
Monolo Juan
- 793
65
votes
5 answers
Is every covariance matrix positive definite?
I guess the answer should be yes, but I still feel something is not right. There should be some general results in the literature, could anyone help me?
Jingjings
- 1,293
- 1
- 11
- 14
65
votes
1 answer
Can someone explain the concept of 'exchangeability'?
I see the concept of 'exchangeability' being used in different contexts (e.g., bayesian models) but I have never understood the term very well.
What does this concept mean?
Under what circumstances is this concept invoked and why?
sxv
- 845
65
votes
7 answers
Are residuals "predicted minus actual" or "actual minus predicted"
I've seen "residuals" defined variously as being either "predicted minus actual values" or "actual minus predicted values". For illustration purposes, to show that both formulas are widely used, compare the following Web searches:
residual…
Tripartio
- 2,176
65
votes
2 answers
A more definitive discussion of variable selection
Background
I'm doing clinical research in medicine and have taken several statistics courses. I've never published a paper using linear/logistic regression and would like to do variable selection correctly. Interpretability is important, so no fancy…
sharper_image
- 787
65
votes
8 answers
Effect of switching response and explanatory variable in simple linear regression
Let's say that there exists some "true" relationship between $y$ and $x$ such that $y = ax + b + \epsilon$, where $a$ and $b$ are constants and $\epsilon$ is i.i.d normal noise. When I randomly generate data from that R code: x <- 1:100; y <- ax + b…
Greg Aponte
- 753
65
votes
3 answers
Cross-Entropy or Log Likelihood in Output layer
I read this page:
http://neuralnetworksanddeeplearning.com/chap3.html
and it said that sigmoid output layer with cross-entropy is quite similiar with softmax output layer with log-likelihood.
what happen if I use sigmoid with log-likelihood or…
malioboro
- 991
64
votes
7 answers
What are alternatives of Gradient Descent?
Gradient Descent has a problem of getting stuck in Local Minima. We need to run gradient descent exponential times in order to find global minima.
Can anybody tell me about any alternatives of gradient descent as applied in neural network learning,…
Tropa
- 885