Why Gene Studies Use Such Tiny P-Values
Take the reading one piece at a time. For each piece: read it once, underline the sentence that says what happens, then look up any word in the list. Tap a word to see its definition.
Piece 1 of 2
A p-value of 0.05 means: if there were truly no effect, you would still see a result this striking about 1 time in 20 by chance alone. Run 1 test at p < 0.05 and you face about a 5 percent chance of a false alarm, which is tolerable. Run 20 tests, all with no real effect, and on average 1 of them crosses p < 0.05 anyway. Run 1,000,000 tests (a GWAS-sized scan), all with no real effect, and on average about 50,000 cross p < 0.05 by chance. This is the multiple-testing logic the synthesis dossier names as the central enemy of genetic studies [DOI:10.1002/bdr2.2216].
Piece 2 of 2
A genome-wide association study of nonsyndromic cleft in Europeans scanned across the genome and reported its top signals only when they cleared the standard bar of p < 5 x 10^-8 (that is 0.00000005), not 0.05 [PMID:31817908, DOI:10.3390/genes10121023]. Hits that did not clear that bar were treated as not yet trustworthy, and the strongest believable signals were expected to repeat in a second independent group before the field accepted them.
Reading the Research
- Skim the title and abstract first to get the gist.
- Circle the one sentence that states the main claim.
- Box the evidence the authors give for that claim.
- Mark one sentence that confuses you, and move on.
Now put it together: In one or two sentences, say what this whole reading is telling you about Mateo. Then go back to the lesson and fill in the guided notes.