Statistical Analysis Stack Exchange
Statistical Analysis Stack Exchange

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1500 questions
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4 answers

Difference between Random Forest and Extremely Randomized Trees

I understood that Random Forest and Extremely Randomized Trees differ in the sense that the splits of the trees in the Random Forest are deterministic whereas they are random in the case of an Extremely Randomized Trees (to be more accurate, the…
RUser4512
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67
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3 answers

What is the variance of the weighted mixture of two gaussians?

Say I have two normal distributions A and B with means $\mu_A$ and $\mu_B$ and variances $\sigma_A$ and $\sigma_B$. I want to take a weighted mixture of these two distributions using weights $p$ and $q$ where $0\le p \le 1$ and $q = 1-p$. I know…
JoFrhwld
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67
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7 answers

Cost function of neural network is non-convex?

The cost function of neural network is $J(W,b)$, and it is claimed to be non-convex. I don't quite understand why it's that way, since as I see that it's quite similar to the cost function of logistic regression, right? If it is non-convex, so the…
avocado
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4 answers

Under what conditions should Likert scales be used as ordinal or interval data?

Many studies in the social sciences use Likert scales. When is it appropriate to use Likert data as ordinal and when is it appropriate to use it as interval data?
A Lion
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66
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4 answers

Perform feature normalization before or within model validation?

A common good practice in Machine Learning is to do feature normalization or data standardization of the predictor variables, that's it, center the data substracting the mean and normalize it dividing by the variance (or standard deviation too). For…
SkyWalker
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2 answers

What does having "constant variance" in a linear regression model mean?

What does having "constant variance" in the error term mean? As I see it, we have a data with one dependent variable and one independent variable. Constant variance is one of the assumptions of linear regression. I am wondering what homoscedasticity…
Mukul
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66
votes
9 answers

List of situations where a Bayesian approach is simpler, more practical, or more convenient

There have been many debates within statistics between Bayesians and frequentists. I generally find these rather off-putting (although I think it has died down). On the other hand, I've met several people who take an entirely pragmatic view of the…
gung - Reinstate Monica
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66
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12 answers

Why do neural networks need so many training examples to perform?

A human child at age 2 needs around 5 instances of a car to be able to identify it with reasonable accuracy regardless of color, make, etc. When my son was 2, he was able to identify trams and trains, even though he had seen just a few. Since he was…
Marcin
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66
votes
5 answers

Best practice when analysing pre-post treatment-control designs

Imagine the following common design: 100 participants are randomly allocated to either a treatment or a control group the dependent variable is numeric and measured pre- and post- treatment Three obvious options for analysing such data are: Test…
Jeromy Anglim
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66
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5 answers

Is adjusting p-values in a multiple regression for multiple comparisons a good idea?

Lets assume you are a social science researcher/econometrician trying to find relevant predictors of demand for a service. You have 2 outcome/dependent variables describing the demand (using the service yes/no, and the number of occasions). You have…
Mikael M
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66
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14 answers

If we fail to reject the null hypothesis in a large study, isn't it evidence for the null?

A basic limitation of null hypothesis significance testing is that it does not allow a researcher to gather evidence in favor of the null (Source) I see this claim repeated in multiple places, but I can't find justification for it. If we perform a…
bkoodaa
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66
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9 answers

Is this chart showing the likelihood of a terrorist attack statistically useful?

I'm seeing this image passed around a lot. I have a gut-feeling that the information provided this way is somehow incomplete or even erroneous, but I'm not well versed enough in statistics to respond. It makes me think of this xkcd comic, that even…
LCIII
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66
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8 answers

Is the R language reliable for the field of economics?

I am a graduate student in economics who recently converted to R from other very well-known statistical packages (I was using SPSS mainly). My little problem at the moment is that I am the only R user in my class. My classmates use Stata and Gauss…
SavedByJESUS
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66
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7 answers

Binary classification with strongly unbalanced classes

I have a data set in the form of (features, binary output 0 or 1), but 1 happens pretty rarely, so just by always predicting 0, I get accuracy between 70% and 90% (depending on the particular data I look at). The ML methods give me about the same…
LazyCat
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66
votes
5 answers

Backpropagation with Softmax / Cross Entropy

I'm trying to understand how backpropagation works for a softmax/cross-entropy output layer. The cross entropy error function is $$E(t,o)=-\sum_j t_j \log o_j$$ with $t$ and $o$ as the target and output at neuron $j$, respectively. The sum is over…
micha
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