Hi,
I'm trying to do a cross-group comparison, where I compare 5 treatment groups (a control group and 4 experimental groups) in terms of a characteristic of the block in which the participants of each group reside (proportion of white residents)
Given that I'm comparing 5 groups, I used a oneway anova with the Bonferroni procedure (syntax and output below).
I'm struggling to understand why the F-test suggests that there is a signficant difference in the mean of the proportion of white residents between the 5 treatment groups, while the p-values of the group-to-group comparison do not suggest that there is a significant difference in any of the pairwise group-to-group comparisons (C and T1, T1 and T2, C and T2, etc.). Given that the F-test suggests that there is a significant difference between groups, I would have expected that to be driven by differences between two pairs of groups or more. Does anyone know how to interpret this or whether I'm misinterpeting the output?
Thank you!
I'm trying to do a cross-group comparison, where I compare 5 treatment groups (a control group and 4 experimental groups) in terms of a characteristic of the block in which the participants of each group reside (proportion of white residents)
Given that I'm comparing 5 groups, I used a oneway anova with the Bonferroni procedure (syntax and output below).
I'm struggling to understand why the F-test suggests that there is a signficant difference in the mean of the proportion of white residents between the 5 treatment groups, while the p-values of the group-to-group comparison do not suggest that there is a significant difference in any of the pairwise group-to-group comparisons (C and T1, T1 and T2, C and T2, etc.). Given that the F-test suggests that there is a significant difference between groups, I would have expected that to be driven by differences between two pairs of groups or more. Does anyone know how to interpret this or whether I'm misinterpeting the output?
Thank you!
Code:
oneway perc_white treatment, bonferroni
Analysis of variance
Source SS df MS F Prob > F
------------------------------------------------------------------------
Between groups 1.16692792 4 .29173198 2.52 0.0399
Within groups 130.64936 1127 .115926672
------------------------------------------------------------------------
Total 131.816287 1131 .116548442
Bartlett's equal-variances test: chi2(4) = 2.1741 Prob>chi2 = 0.704
Comparison of perc_white by treatment
(Bonferroni)
Row Mean-|
Col Mean | C T1 T2_AT2 T2_AT3
---------+--------------------------------------------
T1 | -.060074
| 0.687
|
T2_AT2 | .004283 .064357
| 1.000 0.464
|
T2_AT3 | -.039424 .02065 -.043707
| 1.000 1.000 1.000
|
T3_NA | -.078697 -.018623 -.08298 -.039273
| 0.174 1.000 0.105 1.000
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