Pornography actress productivity

Certain research article titles can make you wonder, "how...?". For example, take this 2017 article by Shinn-Shyr Wang (National Chengchi University, in Taiwan) and Li-Chen Chou (Wenzhou Business College, in China), published in the journal Applied Economics Letters (sorry, I don't see an ungated version), and entitled "The determinants of pornography actress production". It certainly made me wonder, how did they collect the data for that?

It turn out that it wasn't as dodgy as you might first imagine. Wang and Chou used data between 2002 and 2013:

...released by the Japanese ‘Digital Media Mart’, which on a regular basis collects data regarding videos and personal information of the Japanese AV actresses.

Essentially, the study tests whether actresses' physical appearance (proxied by cup size and whether they a side job [*] as a model or entertainer outside the pornography industry), and engagement in risky sex, affect the number of movies the actresses appear in. They find that:

...the later an actress commences her career, the fewer video shots she produces. Cup sizes and experiences as models or entertainers have positive effects on the number of video shots... having acted in risky sex videos could increase the production of an AV actress by more than 60%, which implies that, if the actress is willing to perform risky sex, her production may be significantly increased.

I'm unconvinced by their proxies for physical appearance, and a more interesting study would have addressed this by rating the actresses appearance directly (and no, that wouldn't necessitate the researchers watching loads of porn). The finding in relation to risky sex might be the result of an upward-sloping supply curve (there may be greater demand for riskier sex, so riskier sex attracts higher pay, so the actress works more), but of course there would also be a compensating differential to overcome as well (since riskier sex is probably a negative characteristic of the work, the actress would want to be paid more to compensate them for engaging in it). It would be more interesting to know the results in relation to earnings, rather than production, but I suspect that data is particularly difficult to obtain.

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[*] It seems to me that the pornography might well be the side job, and the modelling or entertainment the main job.