> But I doubt the impacts of rent control would appear in the market this quickly, it'd take years for the market signals to be measurable.

Hard disagree. Rational investors have no problem whatsoever projecting the impact to future cash flows and adjusting the amount they're willing to pay now. That's like saying the stock market wouldn't respond quickly to changes in next year's tax law.

You probably won't see new commencement of building projects, but it probably doesn't mean ongoing projects would be scrapped...

And these things have a lead time of years

> Rational investors have no problem whatsoever projecting the impact to future cash flows and adjusting the amount they're willing to pay now.

That's not accounting for the time value of money.

Suppose you have a rental unit and before rent control you were planning to rent it out. That now has far less attractive returns and it suddenly makes more sense to sell it as a condo to an occupant rather than keeping it to rent it out. Likewise, other prospective landlords no longer want to buy it at the previous market price (returns went down and they can invest in stocks or housing in some other city instead), so the short-term effect is to increase the number of property sellers and decrease the number of buyers. Short-term, property values going down is the expected thing.

But construction going down is also the expected thing, for the same reason. If property values are lower then the number of viable construction projects is lower and less construction happens.

The lack of construction then continues until rents, even after rent control, are high enough to justify more construction, i.e. are even higher than they were originally, because now to justify the same investment as before you need the current rent to be high enough to account for the inability to increase it later. And with less construction happening, that's the natural result in a growing area. More people have to bid on the same number of units, rents go up. So the short-term effect is lower real estate prices, the long-term effect is higher.

Now you say, if we expect real estate costs to be higher later, why don't investors take advantage? Which is the "time value of money" issue. If you invest there now because the prices will be high later, what do you do with the property in the meantime? If you don't rent it out, paying $1 today to get $1 in ten or twenty years is dumb, so you only buy if the current price is at a discount. If you do rent it out, then you'd be stuck trying to sell a building with a rent-controlled tenant, which isn't worth as much as the same building as empty as you bought it which you could sell as condos or rent out at current rents instead of price controlled ones, and then you still need a discount. And so the current seller has to provide a discount even if the real estate costs will be higher in a few years.

The stock market has liquidity, fungibility, low transaction costs, etc etc. https://jlcollinsnh.com/2013/05/29/why-your-house-is-a-terri...

I think you're wildly overestimating the rationality of investors.

In a highly liquid commodity market full of professional traders, I'd agree. But the housing market isn't that liquid over 9 months and there are a lot of small timers. It seems more likely there'd be some sort of initial wobble as sophisticated participants reposition, then a period of calm, then the actual impacts set in over a few years.

It might not happen that way - someone does need to check - but at 9 months I wouldn't read much in to this study. The physical market would still be reorganising and it seems entirely possible that the eventual impacts are just different than what this study suggests. I'd want a period of more like 5 years to be confident that the data had given everyone in the market enough time to feel the impacts of artificially low rents and reposition appropriately.

Except the housing market, especially the rental market, is still significantly driven by small rental property owners and is a significant source of generational wealth transfer.

Starting with the assumption that all or even most investors / actors are rational is a continuing pox on both economic scholarship and societal thinking

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