Yeah, but a few paragraphs later, we have this:

"According to Lokeshwar, potential causes for these declines could be increased obesity/BMI, assay variations, diet/phytoestrogens, declined exercise and physical activity, fat percentage, marijuana use, and environmental toxins."

My personal, totally unsupported hypothesis: society is simply kinder and gentler now. As evidenced by the high testosterone in prison populations, this hormone responds to environmental threats of potential violence.

> My personal, totally unsupported hypothesis: society is simply kinder and gentler now.

Loved reading that. I don't know if it's true, but I hope so.

It's probably not the case that testosterone being lower is a result of society being kinder and gentler, but that society is kinder and gentler as a result of the lower testosterone.

Well, there might be a positive feedback loop factor implied, even if other factors might affect the rise of kinder society and the decrease of testosterone.

That’s funny as the first time I heard about feedback loop was in college biology courses, when we were taught how women hormones interactions are modelizable.

I didn't read it in the former way personally. Your sentence confused me at first with that assumption for you to disprove.

I see that and I'm glad they included it, but ...

Was 1999-2000 that golden age when we all threshed the fields by hand and steered the plows on foot ?

I remember people being quite sedentary and obese then and I don't know that an activity comparison to 1999-2000 has any utility ...

EDIT: OK, I am thinking about this backwards - if, as I suggest, people were just as sedentary in the first period as they are in the second, then the T drop begs a different explanation. As you suggest, they also corrected for age.

So, perhaps, my instinct is wrong. I would still look very closely at the (adjusted, corrected) physical activity before drawing any other conclusions ...

1999-2000 is a period in the past when they had measurements.

I mean ideally they'd have huge numbers of testosterone samples from all of human history, but what are they going to do?

it's a reference point? The article isn't comparing to some platonic ideal of what men's testosterone levels should be...it's just pointing out a statistically significant decrease in those levels over a period of 20 years

There is something double strange about the p values.For the main effect, the broad based decline, p < 0.0001. But for the result for men at "normal" weight, 18.5 < BMI < 24.9, the p value is given as p< 0.05.

The first strangeness is that this hints at a much weaker effect. The second strangeness is reporting the p value rather than the effect size. I clicked the link to a pdf at the bottom of the article, but it is not the paper. shrug