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1500 questions
210
votes
3 answers
Generative vs. discriminative
I know that generative means "based on $P(x,y)$" and discriminative means "based on $P(y|x)$," but I'm confused on several points:
Wikipedia (+ many other hits on the web) classify things like SVMs and decision trees as being discriminative. But…
xyzzyrz
- 3,161
209
votes
4 answers
When should I use lasso vs ridge?
Say I want to estimate a large number of parameters, and I want to penalize some of them because I believe they should have little effect compared to the others. How do I decide what penalization scheme to use? When is ridge regression more…
Larry Wang
- 2,201
- 3
- 13
- 8
205
votes
8 answers
What intuitive explanation is there for the central limit theorem?
In several different contexts we invoke the central limit theorem to justify whatever statistical method we want to adopt (e.g., approximate the binomial distribution by a normal distribution). I understand the technical details as to why the…
user28
205
votes
4 answers
How to determine which distribution fits my data best?
I have a dataset and would like to figure out which distribution fits my data best.
I used the fitdistr() function to estimate the necessary parameters to describe the assumed distribution (i.e. Weibull, Cauchy, Normal). Using those parameters I…
tobibo
- 2,155
- 3
- 13
- 8
201
votes
6 answers
Training on the full dataset after cross-validation?
TL:DR: Is it ever a good idea to train an ML model on all the data available before shipping it to production? Put another way, is it ever ok to train on all data available and not check if the model overfits, or get a final read of the expected…
Amelio Vazquez-Reina
- 19,346
198
votes
5 answers
Why do we need sigma-algebras to define probability spaces?
We have a random experiment with different outcomes forming the sample space $\Omega,$ on which we look with interest at certain patterns, called events $\mathscr{F}.$ Sigma-algebras (or sigma-fields) are made up of events to which a probability…
Antoni Parellada
- 26,280
196
votes
3 answers
What is the difference between a consistent estimator and an unbiased estimator?
What is the difference between a consistent estimator and an unbiased estimator?
The precise technical definitions of these terms are fairly complicated, and it's difficult to get an intuitive feel for what they mean. I can imagine a good estimator,…
MathematicalOrchid
- 2,740
196
votes
13 answers
What is a data scientist?
Having recently graduated from my PhD program in statistics, I had for the last couple of months began searching for work in the field of statistics. Almost every company I considered had a job posting with a job title of "Data Scientist". In fact,…
RustyStatistician
- 1,989
194
votes
8 answers
What is the influence of C in SVMs with linear kernel?
I am currently using an SVM with a linear kernel to classify my data. There is
no error on the training set. I tried several values for the parameter $C$
($10^{-5}, \dots, 10^2$). This did not change the error on the test set.
Now I
wonder: is…
alfa
- 2,695
194
votes
10 answers
Why the sudden fascination with tensors?
I've noticed lately that a lot of people are developing tensor equivalents of many methods (tensor factorization, tensor kernels, tensors for topic modeling, etc) I'm wondering, why is the world suddenly fascinated with tensors? Are there recent…
Y. S.
- 1,277
193
votes
1 answer
Crossed vs nested random effects: how do they differ and how are they specified correctly in lme4?
Here is how I have understood nested vs. crossed random effects:
Nested random effects occur when a lower level factor appears only within a particular level of an upper level factor.
For example, pupils within classes at a fixed point in time.…
Joe King
- 3,805
191
votes
3 answers
How does Keras 'Embedding' layer work?
Need to understand the working of 'Embedding' layer in Keras library. I execute the following code in Python
import numpy as np
from keras.models import Sequential
from keras.layers import Embedding
model = Sequential()
model.add(Embedding(5, 2,…
prashanth
- 4,067
191
votes
80 answers
Statistics Jokes
Well, we've got favourite statistics quotes. What about statistics jokes?
Thylacoleo
- 5,399
- 5
- 26
- 33
188
votes
9 answers
How to summarize data by group in R?
I have R data frame like this:
age group
1 23.0883 1
2 25.8344 1
3 29.4648 1
4 32.7858 2
5 33.6372 1
6 34.9350 1
7 35.2115 2
8 35.2115 2
9 35.2115 2
10 36.7803 1
...
I need to get…
Yuriy Petrovskiy
- 4,139
188
votes
2 answers
How do I get the number of rows of a data.frame in R?
After reading a dataset:
dataset <- read.csv("forR.csv")
How can I get R to give me the number of cases it contains?
Also, will the returned value include of exclude cases omitted with na.omit(dataset)?
Tom Wright
- 2,171