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Thread: ANOVA not significant but Tukey is

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    ANOVA not significant but Tukey is




    I'm still new to stats and would like to know if the results below indicate significance, or at least a trend. Being compared are three independent treatment groups with values from different participants. While an ANOVA does not indicate significance, a Tukey's post-hoc test (indicated below in bold) as well as a t-test between group A and B does.

    Graphpad Prism
    One-way analysis of variance
    P value 0.0572
    P value summary ns
    Are means signif. different? (P < 0.05) No
    Number of groups 3
    F 3.002
    R squared 0.09096

    Bartlett's test for equal variances
    Bartlett's statistic (corrected) 13.42
    P value 0.0012
    P value summary **
    Do the variances differ signif. (P < 0.05) Yes

    ANOVA Table SS df MS
    Treatment (between columns) 201200000 2 100600000
    Residual (within columns) 2011000000 60 33510000
    Total 2212000000 62

    Tukey's Test Mean Diff. q P < 0.05? Summary 95% CI of diff
    A vs B -4265 3.408 Yes * -8519 to -11.32
    A vs C -1290 1.031 No ns -5544 to 2964
    B vs C 2976 2.299 No ns -1424 to 7375

  2. #2
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    Re: ANOVA not significant but Tukey is


    Bartlett's test for equal variances
    Bartlett's statistic (corrected) 13.42
    P value 0.0012
    P value summary **
    Do the variances differ signif. (P < 0.05) Yes
    It looks like the variances may be quite different, you may want to consider performing a version of ANOVA to account for this, such as Welch's.

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