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From |
"RAMPL Linn" <Linn.RAMPL@insead.edu> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
Re: Re: st: How to graph means with correct SE after repeated ANOVA? |

Date |
Fri, 26 Mar 2010 15:04:52 +0100 |

ANOVA? >I am trying to graph the means of a 2-way REPEATED ANOVA in bar charts >and would like to include the correct standard errors. > >Here is how I would do this in a BETWEEN subject 2-way ANOVA: >Linn- >I can see where your going with your code but I think there is an >easier way using -xtmixed- and -margins-. You can use -margins- to >obtain the adjusted cell means along with their standard errors. We >have a web page which covers graphing but not specifically for >repeated measures: >http://www.ats.ucla.edu/stat/stata/faq/mar_graph/margins_graph.htm >Phil Dear Phil and Dave, THANK you so much for your advices. In particularly the URL you gave me, Phil, helped a lot. Since the homepage only provides the information how to graph a dot-chart, here's what I did to graph a bar chart for a 2-way mixed ANOVA including the SE: ------------------------------------------------------------------------ - **** Repeated 2-way anova * Y = diff_rate * subject (repeated) = matlab_file * X1 = trial_2 (0, 1) * X2 = frequency (0, 1) anova diff_rate matlab_file trial_2 / matlab_file#trial_2 frequency / matlab_file#frequency trial_2#frequency, repeated(trial_2 frequency) *marginal means including 95% confidence interval margins trial_2#frequency, asbalanced emptycells(reweight) *saving information from marginal means in matrices matrix b=r(b)' //matrix including means of diff_rate for trial_2 (0, 1) matrix prg=(0\1)#(1\1) /* # is the kronecker product operator */ matrix list prg matrix low=(1\1)#(0\1) /* # is the kronecker product operator */ matrix list low matrix c=prg,low,b matrix list c svmat c, names(c) list c1-c3 in 1/4 matrix v=r(V) matrix v=v[1...,1...] matrix list v matrix se=vecdiag(cholesky(diag(vecdiag(v))))' matrix list se matrix d=b,se matrix list d svmat d, names(d) generate ul = d1 + 1.96*d2 generate ll = d1 - 1.96*d2 list d1-ll in 1/4 * Build a two-way bar graph generate group_trial_2_frequency = . replace group_trial_2_frequency = 0 in 1 replace group_trial_2_frequency = 1 in 2 replace group_trial_2_frequency = 3 in 3 replace group_trial_2_frequency = 4 in 4 twoway (bar d1 group_trial_2_frequency if c2 == 0, color(gs2)) (bar d1 group_trial_2_frequency if c2 == 1, color(gs11)) (rcap ul ll group_trial_2_frequency, blcolor(gs1)) ------------------------------------------------------------------------ - So this finally worked out, thank you so much. However, I am not sure how the "margins" command works after a repeated anova command, since STANDARD ERRORS reported in one group ARE EXACTLY THE SAME: ----------------------------------------------------------------------- | Delta-method | Margin Std. Err. z P>|z| [95% Conf. Interval] -------------+--------------------------------------------------------- trial_2 | 0 | 1.282051 .1263909 10.14 0.000 1.03433 1.529773 1 | -.5940171 .1263909 -4.70 0.000 -.8417386 -.3462956 frequency | 0 | .4679487 .1263909 3.70 0.000 .2202272 .7156702 1 | .2200855 .1263909 1.74 0.082 -.027636 .467807 trial_2#| frequency | 0 0 | 1.435897 .1787437 8.03 0.000 1.085566 1.786229 0 1 | 1.128205 .1787437 6.31 0.000 .777874 1.478536 1 0 | -.5 .1787437 -2.80 0.005 -.8503311 -.1496689 1 1 | -.6880342 .1787437 -3.85 0.000 -1.038365 -.3377031 ----------------------------------------------------------------------- I looked up http://www.ats.ucla.edu/stat/stata/faq/margins_nested1.htm where you see a similar situation for the SE. WHY ARE THE SE exactly the SAME? In particular, the consequence is, that the confidence intervals in one group have the same range (i.e. the same absolute difference). Is this a mistake or correct? If this is correct then graphing confidence intervals in this case would not make a lot of sense...! Thank you so much for any advice! Best Linn * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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