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Latent construct structural equation modeling of the relations among age, self-rated health, and speed was conducted with two samples, each containing 372 adults between 18 and 87 years of age. The major results were confirmed in both samples. Self-rated health, sensory-motor speed, perceptual speed, and reaction time speed all decreased as age increased, but health only partially mediated the relationship between age and speed. There were direct effects of age on all types of speed in addition to the indirect effects of age on speed through the self-rated health measures, and there were direct effects of age on perceptual speed in addition to the indirect effects through sensory-motor speed.
Earles et al. (Sun,) studied this question.