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SelarDorr t1_j7ilxie wrote

Reply to comment by SaltZookeepergame691 in Analysis showed that 65.6% of women who took extra Vitamin D gave birth naturally. The study analysed results from the MAVIDOS trial which involved 965 women being randomly allocated an extra 1,000 International Units (IU) per day of vitamin D during their pregnancy or a placebo. by Wagamaga

i dont see that as a major caveat. you can have a primary study with multiple secondary outcomes, in which the results of the secondary outcomes are just as meaningful as a study in which those outcomes are the primary.

the results of this analysis are still of a randomized double blind placebo controlled trial that directly compared the treatment group to the placebo group for the outcome in question. the fact that these results were not the primary focus of the study does not change its significance.

if it were a case where sample selection for the primary outcome somehow added a confounder for some of the secondaries, i see an argument there. but as far as i can tell, this wasn't the case here.

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leplen t1_j7io778 wrote

Eh, the more secondary outcomes you allow the more you run the risk of multiple comparisons. If the p-valur is low enough I'm fine with it, but otherwise you get into green jelly beans cause acne territory.

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SaltZookeepergame691 t1_j7jdudj wrote

If you don’t have any hypothesis before you do the trial to statistically “test” (ie through null hypothesis testing) any significant result (regardless of multiple comparisons control) you generate is - by definition - hypothesis generating.

I don’t mean that the trial itself isn’t robust. It is. But the finding is not enough on its own to say “this is real”.

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SelarDorr t1_j7kbdrz wrote

the hypothesis exists when you decide what your secondaries are.

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SaltZookeepergame691 t1_j7kcgnv wrote

This is a post hoc analysis. This was NOT a named secondary! It explicitly says so in the paper, and it’s why I explicitly said it was a post hoc analysis…

For your info, from the reg record:

>Primary outcome measure

>Neonatal whole body bone area, bone mineral content and bone mineral density assessed by dual energy x-ray absorptiometry (DXA) within 10 days of birth.

>Secondary outcome measures

>1. Neonatal and childhood anthropometry and body composition (weight, length and skinfold thickness measurements), assessed within 48 hours of birth

>2. Women's attitude to pregnancy vitamin D supplementation (qualitative study; assessed in main study only). Methodology and timepoints of assessment not yet defined as of 03/03/2008

>3. Childhood bone mass at 4 years

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