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help > RE: design matrix for correlation analysis.
Jun 30, 2015 10:06 AM | Andrew Zalesky
RE: design matrix for correlation analysis.
Hi Juan,
If the F-test is replaced with a t-test, it might be useful to lower the statistic threshold. Remember the F=t^2. Therefore, if you use an F-stat threshold of 9, you should probably use a t-stat threshold of sqrt(9)=3 to make the two tests comparable.
Note however that F is two-sided whereas t is one-sided. So even if you sent the statistic threshold to match, there still may be differences in the connections that are found significant.This is expected.
Overall, I think you have just forgot to lower the statistic threshold when using a t-test compared to a F-test.
Andrew
Originally posted by Juan Pablo Princich:
If the F-test is replaced with a t-test, it might be useful to lower the statistic threshold. Remember the F=t^2. Therefore, if you use an F-stat threshold of 9, you should probably use a t-stat threshold of sqrt(9)=3 to make the two tests comparable.
Note however that F is two-sided whereas t is one-sided. So even if you sent the statistic threshold to match, there still may be differences in the connections that are found significant.This is expected.
Overall, I think you have just forgot to lower the statistic threshold when using a t-test compared to a F-test.
Andrew
Originally posted by Juan Pablo Princich:
Dear Professor ;
Will appreciate your comments related to a problem with a design similar to this example, using 5 predictors , F test [0 0 0 0 1] were i get a lot of connections differences for every node (p 0.033) but when i try a T test to define if the correlation is positive [0 0 0 0 1] or negative [0 0 0 0 -1] NBS is unable to detect any difference at all (not significant results).
Using the F test, NBS also detects correlations for the rest of the predictors , for the contrasts [0 1 0 0 0], [0 0 1 0 0] and for the [0 0 0 1 0], but ultimately a T test is only able to detect differences for the contrast [0 -1 0 0 0] and not for any of the others regressors.
Thanks for your time and precious help.
Juan P
Will appreciate your comments related to a problem with a design similar to this example, using 5 predictors , F test [0 0 0 0 1] were i get a lot of connections differences for every node (p 0.033) but when i try a T test to define if the correlation is positive [0 0 0 0 1] or negative [0 0 0 0 -1] NBS is unable to detect any difference at all (not significant results).
Using the F test, NBS also detects correlations for the rest of the predictors , for the contrasts [0 1 0 0 0], [0 0 1 0 0] and for the [0 0 0 1 0], but ultimately a T test is only able to detect differences for the contrast [0 -1 0 0 0] and not for any of the others regressors.
Thanks for your time and precious help.
Juan P
Threaded View
| Title | Author | Date |
|---|---|---|
| Youngmin Huh | Jul 9, 2014 | |
| Andrew Zalesky | Jul 9, 2014 | |
| Juan Pablo Princich | Jun 28, 2015 | |
| Andrew Zalesky | Jun 30, 2015 | |
| Youngmin Huh | Jul 11, 2014 | |