# Lesson 34: Sample Size

### Introduction

So far, in this section, we have focused on using a random sample of size *n* to find an interval estimate for a variety of population parameters, including a mean *μ*, a proportion *p*, and a standard deviation *σ*. In none of our discussions did we talk about how large a sample should be in order to ensure that the interval estimate we obtain is narrow enough to be worthwhile. That's what we'll do in this lesson! Specifically, we'll:

- derive a formula for the sample size,
*n*, necessary for estimating the population mean*μ* - derive a formula for the sample size,
*n*, necessary for estimating a proportion*p*for a large population - derive a formula for the sample size,
*n*, necessary for estimating a proportion*p*for a small, finite population

The methods that we use here in deriving the formulas could be easily applied to the estimation of other population parameters as well.