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1500 questions
59
votes
4 answers
How to identify a bimodal distribution?
I understand that once we plot the values as a chart, we can identify a bimodal distribution by observing the twin-peaks, but how does one find it programmatically? (I am looking for an algorithm.)
venkasub
- 723
59
votes
7 answers
Graph for relationship between two ordinal variables
What is an appropriate graph to illustrate the relationship between two ordinal variables?
A few options I can think of:
Scatter plot with added random jitter to stop points hiding each other. Apparently a standard graphic - Minitab calls this an…
Silverfish
- 23,353
- 27
- 103
- 201
59
votes
4 answers
Multinomial logistic regression vs one-vs-rest binary logistic regression
Lets say we have a dependent variable $Y$ with few categories and set of independent variables.
What are the advantages of multinomial logistic regression over set of binary logistic regressions (i.e. one-vs-rest scheme)? By set of binary logistic…
Tomek Tarczynski
- 4,024
59
votes
2 answers
How can I change the title of a legend in ggplot2?
I have a plot I'm making in ggplot2 to summarize data that are from a 2 x 4 x 3 celled dataset. I have been able to make panels for the 2-leveled variable using facet_grid(. ~ Age) and to set the x and y axes using aes(x=4leveledVariable, y=DV). I…
russellpierce
- 18,599
59
votes
4 answers
Manually Calculating P value from t-value in t-test
I have a sample dataset with 31 values. I ran a two-tailed t-test using R to test if the true mean is equal to 10:
t.test(x=data, mu=10, conf.level=0.95)
Output:
t = 11.244, df = 30, p-value = 2.786e-12
alternative hypothesis: true mean is not…
herbps10
- 693
59
votes
3 answers
What are the values p, d, q, in ARIMA?
In the arima function in R, what does order(1, 0, 12) mean? What are the values that can be assigned to p, d, q, and what is the process to find those values?
kalyani
- 669
59
votes
5 answers
What is the difference between GARCH and ARMA?
I am confused. I don't understand the difference a ARMA and a GARCH process.. to me there are the same no ?
Here is the (G)ARCH(p, q) process
$$\sigma_t^2 =
\underbrace{
\underbrace{
\alpha_0
+ \sum_{i=1}^q \alpha_ir_{t-i}^2}
…
John
- 765
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- 10
59
votes
3 answers
Is it possible to do time-series clustering based on curve shape?
I have sales data for a series of outlets, and want to categorise them based on the shape of their curves over time. The data looks roughly like this (but obviously isn't random, and has some missing data):
n.quarters <- 100
n.stores <- 20
if…
fmark
- 4,977
59
votes
5 answers
Regression when the OLS residuals are not normally distributed
There are several threads on this site discussing how to determine if the OLS residuals are asymptotically normally distributed. Another way to evaluate the normality of the residuals with R code is provided in this excellent answer. This is another…
Robert Kubrick
- 4,528
59
votes
6 answers
Alternatives to logistic regression in R
I would like as many algorithms that perform the same task as logistic regression. That is algorithms/models that can give a prediction to a binary response (Y) with some explanatory variable (X).
I would be glad if after you name the algorithm,…
Tal Galili
- 21,541
59
votes
2 answers
What is the difference between a particle filter (sequential Monte Carlo) and a Kalman filter?
A particle filter and Kalman filter are both recursive Bayesian estimators. I often encounter Kalman filters in my field, but very rarely see the usage of a particle filter.
When would one be used over the other?
Shane
- 12,461
59
votes
3 answers
Logistic Regression: Scikit Learn vs Statsmodels
I am trying to understand why the output from logistic regression of these
two libraries gives different results.
I am using the dataset from UCLA idre tutorial, predicting admit based
on gre, gpa and rank. rank is treated as categorical variable,…
hurrikale
- 903
59
votes
3 answers
How does centering make a difference in PCA (for SVD and eigen decomposition)?
What difference does centering (or de-meaning) your data make for PCA? I've heard that it makes the maths easier or that it prevents the first PC from being dominated by the variables' means, but I feel like I haven't been able to firmly grasp the…
Zenit
- 1,846
59
votes
5 answers
Interpreting QQplot - Is there any rule of thumb to decide for non-normality?
I have read enough threads on QQplots here to understand that a QQplot can be more informative than other normality tests. However, I am inexperienced with interpreting QQplots. I googled a lot; I found a lot of graphs of non-normal QQplots, but no…
greymatter0
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- 12
58
votes
5 answers
Probability distribution for different probabilities
If I wanted to get the probability of 9 successes in 16 trials with each trial having a probability of 0.6 I could use a binomial distribution. What could I use if each of the 16 trials has a different probability of success?
Greg
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