st: Re: Re: Repeated Measures ANOVA: contrasts

["Joseph Coveney" <stajc2@gmail.com>]

David C Airey wrote:

I didn't read far enough in the help file! Page 362 and beyond
for -contrast- has examples with evaluated fractions like
`=1/3' in the linear combination.

--------------------------------------------------------------------------------

I didn't read that far either.  Anyway, if there is substantial autocorrelation,
and if the difference between the average of the first two observations and the
following three is of primary scientific  interest, then the original poster
would perhaps be better off just computing the averages for each volunteer and
performing a paired t-test.  -manova- and -manovatest- (or -contrast-) are out,
with eight volunteers and seven intervals.

Joseph Coveney

. set seed `=date("2014-02-02", "YMD")'

. 
. program define simem, rclass
  1.     version 12.1
  2.     syntax
  3. 
.     drop _all
  4.         set obs 8
  5.     generate byte pid = _n
  6.     generate double fmt1 = rnormal()
  7.     forvalues i = 2/7 {
  8.         generate double fmt`i' = 0.5 * fmt`=`i'-1' + ///
>             sqrt(0.75) * rnormal()
  9.     }
 10.     tempvar a b
 11.     generate double `a' = (fmt1 + fmt2) / 2
 12.     generate double `b' = (fmt3 + fmt4 + fmt5) / 3
 13.     ttest `a' = `b'
 14.     tempname p
 15.     scalar define `p' = r(p)
 16.     drop `a' `b'
 17.     quietly reshape long fmt, i(pid) j(time)
 18.     xtreg fmt i.time, i(pid) fe
 19.     test (1.time + 2.time) / 2 = (3.time + 4.time + 5.time) / 3
 20.     return scalar l = r(p)
 21.     return scalar t = `p'
 22. end

. 
. simulate t = r(t) l = r(l), reps(10000) nodots: simem

      command:  simem
            t:  r(t)
            l:  r(l)


. 
. foreach var of varlist l t {
  2.         generate byte pos_`var' = `var' < 0.05
  3. }

. 
. summarize pos_*

    Variable |       Obs        Mean    Std. Dev.       Min        Max
-------------+--------------------------------------------------------
       pos_l |     10000        .105    .3065687          0          1
       pos_t |     10000       .0511    .2202127          0          1

. 
. exit

end of do-file

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