Re: [R] generating a paired t-test with multiple levels of a factor

From: Peter Dalgaard <p.dalgaard_at_biostat.ku.dk>
Date: Thu, 27 Mar 2008 23:14:52 +0100

Michael A. Miller wrote:
>>>>>> "James" == James Root <jcroot@gmail.com> writes:
>>>>>>
>
> > Is there a way to run all paired t-tests where a paired
> > t-test is run for every possible combination?
>
> Sounds like pairwise.t.test is the sort of thing you are looking
> for...
>
>
Yes, except that it was designed for independent samples t-tests, so you need to be careful about not mixing up the pairs. This appears to do the trick:

> pairwise.t.test(a,col(a),paired=T,pool=F,p.adj="none")

        Pairwise comparisons using t tests with non-pooled SD

data: a and col(a)

  1       2       3       4       5       6      
2 1.4e-08 -       -       -       -       -      
3 1.2e-06 0.65530 -       -       -       -      
4 1.7e-07 0.05903 0.09535 -       -       -      
5 6.1e-08 0.02352 0.17532 0.53276 -       -      
6 0.00355 0.29816 0.10283 0.04843 0.07627 - 7 0.00077 0.14419 0.06035 0.00691 0.02340 0.51667 P value adjustment method: none

> a

    c0 c3 c6 c9 c12 c18 c24
24 150 122 103 109 103 87 109
25 173 127 117 124 143 123 144
26 191 174 165 160 177 184 NA
27 191 159 157 161 150 187 215
28 230 150 144 153 125 124 152
29 145 134 167 141 112 212 194
30 128 92 89 78 83 78 80
31 102 86 80 76 82 79 68
32 180 124 116 117 124 NA NA
33 153 96 97 96 93 156 110
34 115 79 79 79 73 69 72
35 150 113 124 102 100 109 101
36 182 147 156 79 135 NA 162
37 175 146 157 140 143 158 162
38 146 86 81 80 87 89 95
39 92 80 95 95 86 119 NA
40 228 177 185 181 190 182 192
41 178 119 107 NA 102 110 94
42 213 185 152 142 158 178 194
43 161 107 104 107 NA 118 129

> Mike
>
> ______________________________________________
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>

-- 
   O__  ---- Peter Dalgaard             ุster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
 (*) \(*) -- University of Copenhagen   Denmark      Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalgaard_at_biostat.ku.dk)              FAX: (+45) 35327907

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Received on Thu 27 Mar 2008 - 22:19:05 GMT

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