Can rodent longevity studies be both short and powerful?

Abstract

Many rodent experiments have assessed effects of diets, drugs, genes, and other factors on life span. A challenge with such experiments is their long duration, typically over 3.5 years given rodent life spans, thus requiring significant time costs until answers are obtained. We collected longevity data from 15 rodent studies and artificially truncated them at 2 years to assess the extent to which one will obtain the same answer regarding mortality effects. When truncated, the point estimates were not significantly different in any study, implying that in most cases, truncated studies yield similar estimates. The median ratio of variances of coefficients for truncated to full-length studies was 3.4, implying that truncated studies with roughly 3.4 times as many rodents will often have equivalent or greater power. Cost calculations suggest that shorter studies will be more expensive but perhaps not so much to not be worth the reduced time.

Figure 1.

Ratios of variance in effect estimates in truncated versus full life-span studies as a function of proportion of animals dying in truncated study. *The curved line represents a least squares second order polynomial fitted to the data. ** The numbers on the left side of the y-axis represent the log scale, whereas the numbers on the right side of the y-axis represent the absolute scale.