Fig. 4: Linear relationships between measured mean oxygen saturation values and each of three independent variables exhibiting the strongest correlation with these metrics.
From: Pulse oximetry values from 33,080 participants in the Apple Heart & Movement Study
a–c (top row) correspond to mean daytime SpO2. d–f (bottom row) correspond to mean nocturnal SpO2. Independent variables consist of: a, d age, b, e body mass index, c, f home altitude. Each plot presents a 2-dimensional histogram of values from all 33,080 subjects in evenly spaced hexagonal bins, with the color density corresponding to log-scaled bin counts for visual clarity. In each plot, the overlaid red line represents the simple univariate linear regression fit using the independent variable shown on the x-axis. The listed slope and Pearson correlation coefficient correspond to the same univariate linear fit.
