If each of the following measurements were to be taken on a group of 50 college students (once only for each student), it is unlikely that all 50 of them would yield the same value. In other words, there would be variability in the measurements. In each case, explain whether their values are likely to differ because of natural variability across time, natural variability across individuals, measurement error, or some combi­nation of these three causes.
a. Systolic blood pressure
b. Time on the student’s watch when the actual time is 12 noon