Comments on Can pregnant women intuit the sex of their children?

By: Akhila

2015-09-28T05:55:08Z

It’s a wonder to observe that the distribution became a normal one. Awaited follow-up study

By: JG42

2015-04-19T03:41:06Z

I have to be cynical and think that a few of the women had access to ultrasound data beforehand and used that as a guess. That said, I would love to see a follow up study.

By: Matt Asher

2015-03-09T00:43:17Z

Skepticism is always warranted. Here’s want Shamas told me about publishing:

“Our study was not published in a peer-review journal because I had intended to do a follow-up study that would serve to replicate and extend these findings. In the meantime, the birth center was sold and the director who had been amenable to our research left her position; the graduate student transferred to another program; and my own career interests took me in other directions.”

By: Dean Eckles

2015-03-07T05:22:22Z

Where can I find a fuller report on this study (eg the journal article or such)?

By: Dean Eckles

2015-03-07T05:21:06Z

Do you have a link to the actual study? The link seems to just be an old USA today article. And Google Scholar doesn’t turn much up:
http://scholar.google.com/scholar?q=author%3AAmanda-Dawson+author%3Avictor-shamas&btnG=&hl=en&as_sdt=0%2C33

Makes me a bit more skeptical there isn’t anything else to the study design.

By: Aidan

2014-12-15T18:41:32Z

Great read!

By: Tom

2014-12-15T01:39:16Z

I love the use of the blogosphere for keeping journalists honest. Thank you!

The biological mechanism is only one item in the Bradford Hill Criteria (http://en.wikipedia.org/wiki/Bradford_Hill_criteria). I know there are plenty of treatments we don’t entirely understand the mechanics of but are strongly recommended. And I’m not even a doctor! Take tuberculosis treatment for example. Why does WHO recommend 6 months? Why don’t the drugs kill off everything in 6 weeks? Why not 10 months? We don’t know how those little bugs hide and elude the drugs, but we do know relapse rates climb quickly for less than 6 months treatment. We’ll figure out why someday, but we’re confident to act accordingly in the meantime.

@Victor Shamas, you can have 4 more datapoints for your hypothesis generation. 🙂 My wife and I predicted the sex on all 4 of our children (2 boys, 2 girls) before even the first ultrasound. It’s actually quite easy. She vomits about 100x as frequently with a girl as with a boy.

By: Victor Shamas

2014-12-12T16:00:28Z

Thanks, Matt, for a wonderful blog. We often see in science that people hold findings to a much higher standard when those findings do not fit their conceptual framework.

When Amanda and I presented our initial findings in a departmental colloquium here at the University of Arizona, a visiting neuropsychologist objected, arguing that our findings could have been due to chance. I found it pretty amusing given that he had made his career on the study of a phenomenon called blindsight, which is based on the observation of an occurrence 59% of the time (compared to chance, which is 50%). Our effect size was over 70%, and there was no question about statistical significance.

As you point out, there are ALWAYS methodological issues that can be raised with any study. We researchers try to do the best we can in designing our studies, but as far as I know, the perfect research study has yet to be designed. There is always more to know and questions to be answered. The most beautiful thing in science is the power of replicability. If you doubt what we did, you can run your own experiment. In this case, I have the original survey and would more than welcome someone to replicate our now 16-year-old findings.

Then there is the question of mechanism to be addressed. If in fact these women did have accurate intuitions concerning the sex of their unborn children, what was the basis of those intuitions? I don’t have a definitive answer to that question but am more than happy to offer my speculation, which is perfectly legitimate with respect to the scientific process. After all, this type of speculation is how new hypotheses are generated.

By: Adam

2014-12-12T13:11:57Z

One of my arguments is that you need to specify your significance before any analysis, and then give a binary accept/reject result. One problem with using the magnitude of the p-value to identify significance is that people will tend to make comparisons using them. If the NFL conducted two experiments (one with the AFC and one with the NFC) and found the significance level was 0.03 for the AFC and 0.0001 for the NFC, would you say we should choose the NFC coin? Is the AFC coin, if repeated, capable of producing 0.0001 significance?

The biggest danger is in comparing p-values. If you had a regression model with 10 variables and examined p-values, why not just turn it into a linear regression with the single highest p-value?

By: Matt Asher

2014-12-12T12:54:47Z

Hi Adam! Perhaps because I’m not a “p-value purist”, I find the idea that a smaller p-value doesn’t increase confidence intriguing, but hard to understand. Imagine you were hired by the NFL to test whether their super-bowl coin is fair. You have time for 20 tosses, then you have to make a recommendation about whether they should replace the coin. Wouldn’t you feel more confident telling the league to replace their coin if the results landed well into the (pardon me) tails of the distribution? What if replacing the coin is expensive and complicated, is your pre-chosen significance level the cutoff and the exact value irrelevant?