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ANOVA, post hoc tests, F statistic and p values.

  • 25-09-2009 3:29am
    #1
    tech77
    Closed Accounts Posts: 2,736 ✭✭✭


    Hi.
    Say i do a one-way ANOVA looking at the difference between 4 treatment groups (4 levels of a factor).
    I get a p value of <0.05. OK that's significant.

    But let's say only one pair of the 4 treatment groups are different from each other on the post-hoc Newman-Keuls test.

    Just wanna check what that means:
    Does that mean that the significant difference between treatments really only applies to that pair and the rest are not different.

    So for the significantly different pair, i can report F=whatever, P<0.05.

    But if i wanted to report the result of one of the other pairs i couldn't say p<0.05. I'm guessing then that i can't report the F statistic either for these pairs as that is the "tethered" to the significant p value isn't it- (which in turn of course is only relevant to the significant pair).

    So is there anything (non-significant F or p values etc) that i could report about the non-significant pairs.

    Also, i'm trying to do a 2 way ANOVA on a couple of stats packages (minitab, GraphPadPrism) but because of one or two missing data points/slightly unequal cell sizes, they can't do it (useless pieces of crap :P ).
    Instead of doing a 2 way ANOVA, can you just do a separate one-way ANOVA for each of the 2 factors. I know you wouldn't get the interaction statistic but otherwise would it be OK?
    I'm guessing not. :)

    Any help would be great thanks. :)


Comments

  • #2
    Victor
    Registered Users, Registered Users 2 Posts: 78,644 ✭✭✭✭Victor


    tech77 wrote: »
    So is there anything (non-significant F or p values etc) that i could report about the non-significant pairs.
    You can report that they are non-significant (whether marginal or not), stating the usual stats.


  • #3
    tech77
    Closed Accounts Posts: 2,736 ✭✭✭tech77


    Victor wrote: »
    You can report that they are non-significant (whether marginal or not), stating the usual stats.

    Yeah, but what are the usual stats for them.

    They don't seem to have a p value (the p value of <0.05 refers to the significant pair only) and i don't think the F value refers to them either, does it?

    What are the stats that refer to a non-significant pair like this?

    is it the q value- that's something i've seen mentioned opposite the non-sig stuff.

    Thanks.


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