tag:blogger.com,1999:blog-3724376948636627084.post5880929653469786199..comments2024-03-20T21:38:10.502+00:00Comments on Science matters: Ascertainment BiasBobTheScientisthttp://www.blogger.com/profile/02038631019672961663noreply@blogger.comBlogger4125tag:blogger.com,1999:blog-3724376948636627084.post-1072221830418315542021-08-04T14:33:46.290+01:002021-08-04T14:33:46.290+01:00Thanks for all that Steve. It's a bit like all...Thanks for all that Steve. It's a bit like all the data about "all humanity" which is just the responses of WEIRD undergraduates who happen to take psych and economics classes when the profs are getting the chains jangled for more research outputs.BobTheScientisthttps://www.blogger.com/profile/02038631019672961663noreply@blogger.comtag:blogger.com,1999:blog-3724376948636627084.post-72215033180935900732021-08-04T14:19:20.183+01:002021-08-04T14:19:20.183+01:00... and while I'm at it. The first PhD student...... and while I'm at it. The first PhD student of the late great population geneticist Theodosius Dobzhnasky was Chinese. He returned to China at the beginning of the Sino-Japanese War, and was assigned to do medical checkups of army recruits. Thinking to make the checkups do double duty, he also asked about 'tongue rolling', the archetypal ability to roll the tongue into a 'U' shape which at the time was considered a simple Mendelian trait. Oddly, recruits were 'rollers' at a much lower rate than in other populations examined, and he thought he had something. The Ascertainment Bias was realized only years later: recruits, being asked if they could roll their tongues, thought that inability to do so would make them unfit for military service (like flat feet), so they lied. More recent counts show that Han Chinese show typical incidence; the trait is now known not be a simple Mendelian character.Steve Chttps://www.blogger.com/profile/07895546822943275299noreply@blogger.comtag:blogger.com,1999:blog-3724376948636627084.post-20967011065340847132021-08-04T14:04:14.805+01:002021-08-04T14:04:14.805+01:00Reviewing this while going through old email: the ...Reviewing this while going through old email: the other means to overcome the classroom mechanics is simply to come prepared with a set of "data" that demonstrates the point (if this makes you squeamish, use last year's data) and appear to do the calculations cold, while having the answers available. NB: after years of student's apparently drinking the reagents for the PCR lab, I have shifted to having each component of the rxn mix be colored H20. Use indicators if you like. Put the tubes in a PCR machine adjusted to do 10 turbo cycles in 30 min, so that everyone can observed the temperature shifts, then whisk the results to another room and replace with pre-dispensed size markers. Students run these out in gels. Announce one of the bands as the PCR product, and have students estimate size from the remainder. Change the band chosen from lab to lab, or year to year. [You can of course pre-prepare an actual PCR amplification product, and run it in combination with or parallel to the size markers].<br /><br />Steve CSteve Chttps://www.blogger.com/profile/07895546822943275299noreply@blogger.comtag:blogger.com,1999:blog-3724376948636627084.post-73678470028973565352014-02-06T14:39:54.703+00:002014-02-06T14:39:54.703+00:00Nice data set. Classroom mechanics intrude.
(1) ...Nice data set. Classroom mechanics intrude. <br /><br />(1) The sex ratio in most intro biology classrooms will be biased towards women, often strongly. This biases the expected end result, that total numbers of male and females sibs should be 1:1. [You didn't mention the sex ratio in your 25 students].<br /><br />(2) In a large lecture hall, toting up sibships for 100+ students is tedious. So, ask all women to stand, take a count, then ask all women with brothers to sit. Repeat head count, ask all women with sisters to sit, then count all remaining standees, who are female only-children. The AB point is made swiftly and intuitively, semi-quantitatively, and participatively. <br /><br />(3) Fisher's math applies to the primary sex ratio (at conception, or birth), and bright lads and lasses will observe that there are more old ladies than old men. But it always corrects itself in the next generation.<br /><br />(4) Newfoundland has a history of Irish Catholic and English Protestant settlement, the former with large families and the latter with small. This persists (you will be quizzed by parents of your date on this point). Protestants *tend* to stop after a first-born boy, less so after a girl, Catholics just keep on going. The advanced student may model sex ratio with a 1:1 birth expectation, and full stop after the first boy.<br /><br />Steve C. (Memorial U: three-generation ex William from Co Fermanagh. See if you can guess)Unknownhttps://www.blogger.com/profile/05436036803789868645noreply@blogger.com