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From |
"Nick Cox" <n.j.cox@durham.ac.uk> |

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

Subject |
RE: st: Difference of means and t-test |

Date |
Mon, 14 Jun 2010 20:25:07 +0100 |

I don't think our views are contradictory. It is clearly true that you can get results from summary statistics alone. But erecting fake Gaussians with those summaries is not equivalent to reconstructing the original data. That is my point, and no more. It is akin to arguments at a higher level about "sufficient statistics". If something is normal, then it is sufficient to know mean and sd, but there isn't a reverse argument. Nick n.j.cox@durham.ac.uk Richard Williams At 11:19 AM 6/14/2010, Nick Cox wrote: >-- except that will surely overstate the strength of the conclusions, in >so far as the real distributions are unlikely to be exactly Gaussian. I don't believe that is correct. You can often get by with only having the summary statistics, which is why things like ttesti work. Consider the following example (probably clunkier than necessary but functional): First i use the real data to compute an anova. Then, using the reported Ns, means, and standard deviations, I create 4 fake data sets, append them together, and run the anova again. Results are identical. There is obviously no reason to do this if you have the real data, but stuff like this may be handy if you only have published results to go by. use "http://www.indiana.edu/~jslsoc/stata/spex_data/ordwarm2.dta";, clear oneway age warm, t corr2data age, n(297) mean(50.468013) sd(16.627471) clear gen warm = 1 save warm1 corr2data age, n(723) mean(48.255878) sd(17.365776) clear gen warm = 2 save warm2 corr2data age, n(856) mean(42.23715) sd(16.329103) clear gen warm = 3 save warm3 corr2data age, n(417) mean(40.776978) sd(14.480446) clear gen warm = 4 save warm4 clear all append using warm1 warm2 warm3 warm4 oneway age warm, t Pages 8-10 of the following handout show how you can do OLS regression when you only have the means, standard deviations and correlations available to you. (It also shows you what you can't legitimately do): http://www.nd.edu/~rwilliam/stats1/OLS-Stata9.pdf * * 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/

**References**:**st: Difference of means and t-test***From:*mmolina@uniroma3.it

**Re: st: Difference of means and t-test***From:*Richard Williams <richardwilliams.ndu@gmail.com>

**RE: st: Difference of means and t-test***From:*"Nick Cox" <n.j.cox@durham.ac.uk>

**RE: st: Difference of means and t-test***From:*Richard Williams <richardwilliams.ndu@gmail.com>

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