# How does SPSS compute the Bonferroni adjusted alpha used in their >2x2 Chi-square tests?

4 messages
Open this post in threaded view
|
Report Content as Inappropriate

## How does SPSS compute the Bonferroni adjusted alpha used in their >2x2 Chi-square tests?

 My question concerns how SPSS v22 does Bonferroni corrections for chi-square tests on contingency tables > 2x2 (nominal data). For example when doing the post-hoc pair-wise comparisons between the 4 groups (in columns), are the adjustments based on just the row or the whole matrix? For the former, the adjusted alpha level (threshold) would be 0.0083, (.05/6); for the latter it would seem to be .00167 (.05/30). Which are they using to declare that a p-value is significant, while preserving the experiment-wise alpha of 0.05? Their documentation is unclear on this issue.
Open this post in threaded view
|
Report Content as Inappropriate

## Re: How does SPSS compute the Bonferroni adjusted alpha used in their >2x2 Chi-square tests?

 You can find the adjustment formula in the Algorithms documentation under CROSSTABS.  It is based on the subtable in the column proportions test.On Thu, Oct 13, 2016 at 8:39 AM, Emet Schneiderman wrote:My question concerns how SPSS v22 does Bonferroni corrections for chi-square tests on contingency tables > 2x2 (nominal data). For example when doing the post-hoc pair-wise comparisons between the 4 groups (in columns), are the adjustments based on just the row or the whole matrix? For the former, the adjusted alpha level (threshold) would be 0.0083, (.05/6); for the latter it would seem to be .00167 (.05/30). Which are they using to declare that a p-value is significant, while preserving the experiment-wise alpha of 0.05? Their documentation is unclear on this issue. -- View this message in context: http://spssx-discussion.1045642.n5.nabble.com/How-does-SPSS-compute-the-Bonferroni-adjusted-alpha-used-in-their-2x2-Chi-square-tests-tp5733251.html Sent from the SPSSX Discussion mailing list archive at Nabble.com. ===================== To manage your subscription to SPSSX-L, send a message to [hidden email] (not to SPSSX-L), with no body text except the command. To leave the list, send the command SIGNOFF SPSSX-L For a list of commands to manage subscriptions, send the command INFO REFCARD -- Jon K Peck[hidden email] ===================== To manage your subscription to SPSSX-L, send a message to [hidden email] (not to SPSSX-L), with no body text except the command. To leave the list, send the command SIGNOFF SPSSX-L For a list of commands to manage subscriptions, send the command INFO REFCARD
Open this post in threaded view
|
Report Content as Inappropriate

## Re: How does SPSS compute the Bonferroni adjusted alpha used in their >2x2 Chi-square tests?

 You can find the adjustment formula in the Algorithms documentation under CROSSTABS.  It is based on the subtable in the column proportions test. Jon - Thanks for pointing me to the documentation.  If I understand it correctly, the Bonferroni corrections are computed on a row by row basis, and do not account for the total number of rows in the contingency table (i.e., treated as independent). For example with a 6x4 contingency table (6 response levels in the rows and 4 groups in columns),  there are 6 possible pairwise comparisons per row, so the adjusted alpha level (threshold) would be 0.00833, (.05/6).  Is this your understanding?