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From |
Joerg Luedicke <joerg.luedicke@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Sample size calculations |

Date |
Thu, 14 Mar 2013 11:13:02 -0400 |

As Nick said, it does not seem to be quite clear what exactly you would like to do. Are the data that you have some kind of pilot data and you are planning a larger study? In any case, your input information is not sufficient: a) The effect sizes you mention are meaningless without knowing anything about the variance of your outcome measure. That is why people often use some flavor of standardized effect sizes. Simply put, if your outcome variance (or better yet: the variance of the Gaussian error in your assumed linear model) is very large, then an effect of 7 might be quite small, whereas if the variance in the outcome is small, 7 might be quite large. b) You don't say what exactly these effects are. Are these differences between certain ethnic groups? Differences to some reference values? c) What do you mean with "parameter p"? In any case, stuff like this is probably best done with a bunch of simulations. Perhaps have a look at Al Feiveson's article: http://www.stata-journal.com/article.html?article=st0010 and go from there. Joerg On Thu, Mar 14, 2013 at 10:01 AM, Amal Khanolkar <Amal.Khanolkar@ki.se> wrote: > Hi, > > I plan to run a set of multivariate linear regressions models which will help analyze ethnic differences in my outcome of interest. > > regress Y i.ethnicity age i.education height bmi bloodpressure > > I have 14 different ethnic groups. > > As some of my ethnic groups are fairly small I would like to calculate the sample size needed for each of the fourteen ethnic groups. I have a rough idea of the expected effect or parameter p in each ethnic group. > > I've only calculated sample sizes for a two group comparison using the sampsi command in Stata. > > Does anyone know how I could go about testing expected sample sizes for several categories of the exposure variable? > > I would set other parameters needed to calculate sample size as follows: alpha=0.05, power (0.90), expected effect for most ethnic groups varies between -2.85 to -7.65 > > Thanks & regards > > Amal > > > > > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/faqs/resources/statalist-faq/ > * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/

**References**:**st: Sample size calculations***From:*Amal Khanolkar <Amal.Khanolkar@ki.se>

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