For each probe, a linear-spline model of expression across age was fit with a single change point. The change point was allowed to vary across the entire age range, and the change point that produced the lowest meansquared error was selected as the expression turning point for that probe. Data within the first and last decade of the range interrogated (0–10 and 70–80 years) were excluded to avoid edge effects (n = 7,272 probes). See Fig. 1b (grey histogram).
