Gather round ye endogeneity taliban, for the people have been lead astray. They have listened to the psychologists and erected false idols, replacing their devotion to RCTs and quasi experimental methods with worship for panel data models - forgetting entirely their duty to have a real identification strategy.

A summary of the problem: a psych metanalysis of the literature on how spanking affects children was recently published. While it dutifully has a "oh yeah, btw, none of this is causal" tossed into its conclusion, it doesn't truly understand just how squonked that literature really is. You see, the paper realize that it's no good that 70% (exactly) of the literature it surveys is cross sectional. But then it notes that the longitudinal studies also see similar effects, proudly reminding us that longitudinal studies have "strong" research designs because the spanking temporally precedes the outcomes measured in the study. The 4 experimental studies in that metanalysis find weaker results on the effect of spanking, and are all profoundly limited. Naturally, the psych people employ no quasi experimental methods.

Oh boy. Look. It's not enough to have a one liner about how maybe parents that spank their kids are different from parents that don't. That's not an incidental issue that probably averages out to 0. If parental investment in children is negatively associated with being the kind of parent that spanks children, you get a negative effect of spanking on child outcomes unrelated to the actual spanking itself. Even if your study is using within family variation, parents may invest less in trouble maker kids that they spank. Even if your study does a difference in difference looking at (trouble maker vs non trouble maker) child outcomes in spanking vs non spanking families, you still have the problem that spanking parents may be differentially less able to parent trouble maker children - perhaps due to their own lack of the additional economic or cognitive resources required to do so. (Not that the psych literature did this. Think of this part as an R1 of their future literature.)

So, what do we have? A literature on the effect of spanking that is hopelessly bogged down in the swamps of endogeneity. A metanalysis of that literature that technically admits this, but doesn't take that seriously.

And of course, an army of r/science redditors + journalists aggressively interpreting these correlations as causal. Some people are wise enough to asterisk this with correlation vs causation type boilerplate, and some even seem to really understand that issue. But for every post like that, there's another post that says "Yeah but it's a metanalysis so it must be right" (garbage in, gold out) or - worse - "Yeah, but it's confirmed by panel studies - the spanking happens first, so it isn't reverse causality and we're good" (endogeneity don't real).

Oh well, let's be constructive for a moment. How would an empirical micro economist address this? What sorts of variation might we try to use? Things we might try include looking for an effect via assignment to teachers that do or do not spank their students (where and when this was legal). You might exploit variation induced by laws banning spanking in schools. Another might try to exploit assignment in the foster care system to foster parents that do or do not spank. Going forward, you could run experiments trying to persuade randomly chosen parents to stop spanking. Maybe you can find natural experiment versions of this in the past, where perhaps there were such persuasion campaigns via public TV or something. None of these study ideas are perfect. They don't solve every issue. But at least their identification strategy is better than "spanking happened before the outcome variable, so we're probably ok".

Author's disclosure: I do not know anything about what spanking really does. I do not care what it really does. I profoundly hope that anyone that believes they know the true effect of spanking does not share that alleged wisdom in this thread.

Tldr: repent to the true faith, as detailed literally in the text of Mostly Harmless Econometrics.