惊人趋势背后的测量、样本与因果难题
A reported halving of average testosterone over five decades sounds like a single, sweeping biological fact. In practice, a population trend is assembled from measurements taken from different cohorts, often with changing assays, sampling frames and health profiles.
Researchers can adjust statistically for age or body composition, but adjustment cannot automatically identify a cause. Medication use, environmental exposure, chronic illness, sleep, smoking and selection into a study may shift together across generations.
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