This piece assesses common ways states have combined data over the subgroup - grade level - year level to increase effective sample size and statistical reliability. (educationnext.org)
We then approximate this distribution with a binomial distribution by fitting the mean and the variance of the binomial distribution to the bootstrapped distribution, yielding an effective sample size of 18.4 individuals. (academic.oup.com)
However, geophysical data are often autocorrelated, which has the effect of reducing the effective sample size of the data. (nap.edu)