You people are writing my posts for me. On my recent post about descriptive vs. hypothesis driven research commenter Whimple picked up what I thought was a fairly dead thread… and said (among other things)…
“Is the difference between a descriptive hypothesis and a mechanistic hypothesis that the mechanistic hypothesis is falsifiable?”
Regular and thoughtful commenter DSKS replies…
A hypothesis must be falsifiable period, whether broad and weakly-focused (omics, “fishing expeditions” and so forth) or narrow and explicit. I think the latter is what is often referred to as “mechanistic” science, even though all science is ultimately directed towards establishing cause.
I think the current brouhaha about “descriptive science” conflates two separate issues best described by the following examples:
1) The serendipitous discovery: The investigator is testing her prediction that Treatment A will increase Variable X. During analysis, however, she discovers a trend indicating that Treatment A also appears to have changed Variable Y.
2) The fishing expedition: The investigator enters a fledgling research field regarding a new disease for which little is known of the cause. He proposes to do a genetic screen to see whether the disease is simply a result of a genetic defect. He finds that expression of genes X, Y and Z is deficient in all patients with the disease, but no patients in the control group.
(1) is hypothesis-free and (2) is hypothesis-driven. Both are clearly hypothesis-generating. Under current standards, (1) cannot be published without at least designing new experiments to test the hypothesis that Treatment A affects Variable Y (only on this subsequent data can statistics be applied; assessments of probability post hoc are invalid). (2) Satisfies the hypothetico-deductive model completely, and the issue determining publication will be the impact of the work and the reliability of the methodology.
Very clever that. But here are the random things that bug me about these two types of hypotheses. In the case of #1, will the investigator notice the unexpected effect if it is not within their hypothesis? I’d love to think that we always do- but do we bias ourselves in what we look at during the experiment that we are using to test a narrow mechanistic hypothesis. Is the investigator in case 1 likely to notice the unexpected effect OUTSIDE the proposed hypothesis… can, and do, we bias ourselves by this kind of thinking?
Second- still in regard to #1- how likely is it that the investigator does what DSKS proposes (design new experiments to test a new hypothesis)… and doesn’t just ‘adjust’ the original hypothesis and hammer out a paper. I’d love to think that’s not the way things work… but am I hopelessly naive?
And finally- on #2- As DSKS points out screens ARE hypothesis driven, just not the same flavor of hypothesis used in case #1… and maybe better… since it would be tough to bias the screen by having an idea of the outcome in your head in advance. Of course, screens can be screwed up too- and I’m not meaning to suggest that they are completely without bias… surely not… you get what you ask for in a screen.