Statistics Help @ Talk Stats Forum - Biostatistics
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Epidemiology and biostatistics, public health research. GLM, logistic regression, survival analysis, clinical trials.enThu, 02 Jul 2015 09:28:06 GMTvBulletin60http://www.talkstats.com/images/misc/rss.pngStatistics Help @ Talk Stats Forum - Biostatistics
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Incongruity between t-test and 2x2 repeated measures ANOVA/gain scores t-test/ANCOVA
http://www.talkstats.com/showthread.php/61454-Incongruity-between-t-test-and-2x2-repeated-measures-ANOVA-gain-scores-t-test-ANCOVA?goto=newpost
Wed, 01 Jul 2015 15:54:45 GMTHi,
it's the first time I post here. Forgive me if my English is not always correct.
I want to ask about an incongruity I found when analyzing data from a randomized controlled trial.
I briefly explain the study: pre-post study to assess the efficacy of an intervention in promoting physical fitness; 1 intervention group and 1 control group; physical fitness assessed pre and post the intervention period, for both groups.

Now let's come to the problem:
- running a t-test for intervention group (pre VS post) I found statistically significant difference.
- running a t-test for control group (pre VS post) I did not find statistically significant difference.
So, I could say intervention improved physical fitness, while in control group there were no significant changes in physical fitness.
- but, when running a 2x2 (group x time) repeated measures ANOVA I didn't find any significant difference; the same happened trying to compare gain scores (pre-post change scores) of the 2 groups with a t-test, or when running an ANCOVA on post-scores using pre-scores as covariate.

Can someone explain this to me? Should I consider the results from rm-ANOVA, gain scores t-test and ANCOVA, since the changes in control group were not significant at first while those in the intervention group where significant?
Thanks everyone!
]]>BiostatisticsArtanishttp://www.talkstats.com/showthread.php/61454-Incongruity-between-t-test-and-2x2-repeated-measures-ANOVA-gain-scores-t-test-ANCOVAHow do I chose between sensitivity/specificity and PPV/NPV?
http://www.talkstats.com/showthread.php/61421-How-do-I-chose-between-sensitivity-specificity-and-PPV-NPV?goto=newpost
Mon, 29 Jun 2015 16:56:19 GMTI have just finished a validation study, where two specialists used the available information to classify patients according to their diseases status...I have just finished a validation study, where two specialists used the available information to classify patients according to their diseases status as true cases and no cases. I have confirmed diagnoses for a sample of those patients and I now want to see how successfully the specialists evaluated the disease status of those patients.

I tried to find it out myself but I still don't fully understand the difference between sensitivity and PPV resp. specificity and NPV. Which of those values are relevant for my analysis? Is it necessary to present all four values or is it enough to just present the PPV and NPV?

Thank you for your help! This is probably a really basic question but I did not really find an answer to it myself.
]]>Biostatisticsmarsh_randyhttp://www.talkstats.com/showthread.php/61421-How-do-I-chose-between-sensitivity-specificity-and-PPV-NPV