spm1d

Multivariate post hoc analysis

Post hoc analyses are currently in development.

As a rule-of-thumb, NEVER report post hoc results which disagree with the main test results. If the results disagree, the post hoc procedures are too simple.

If you report post hoc results for spm1d analyses please explicitly highlight the limitations described in this document.

Warning

Current post hoc procedures in spm1d are likely too simple.

The example belowe uses a simple Bonferroni correction, but this assumes that the post hoc tests are independent, which is usually not the case, especially for multivariate data.

Danger

Current post hoc procedures in spm1d are generally not valid.

They are not valid because they involve separate smoothness assessments for each post hoc test.

Although the resulting errors are expected to be small, we cannot guarantee validity.

Suggestions for conducting post hoc analyses for multivariate tests:

  • For each post hoc test use a Bonferroni correction.
  • For Hotelling’s T2 tests conduct separate t tests on each vector component, but acknowledge that this neglects vector component covariance.
  • For CCA conduct separate regression tests on each vector component, but acknowledge that this neglects vector component covariance.
  • For MANOVA conduct separate Hotelling’s T2 tests on each pair of groups, and if those tests reach significance then conduct additional post hoc t tests on each vector component, but acknowledge that this neglects vector component covariance.