This document discusses interval estimation and estimation of proportions from sample data. It defines an interval estimate as a range of values (L1 to L2) that is likely to contain the true population parameter. A 100(1-α)% confidence interval is an interval where the probability of the parameter falling within the interval is 1-α. For large samples where the population variance is known, the confidence interval for the mean is calculated. For small samples or unknown variance, approximations are used. Estimation of a population proportion p is discussed, where the sample proportion p=X/n is an unbiased estimator of p. For large samples, a normal approximation can be used to construct a confidence interval for p. Sample size determination is