Which one of the following statements is true about the dispersion of the distribution of sample means?
a) The dispersion of the distribution of sample means is always equal to the dispersion of the population.
b) The dispersion of the distribution of sample means tends to decrease as the sample size increases.
c) The dispersion of the distribution of sample means is independent of the variability of the population.
d) The dispersion of the distribution of sample means is always greater than the dispersion of the population.