Question

We want to sample from a single book, the number of words in a sentence. It is decided that only 20 sentences will be selected and for each one selected, the number of words in that sentence will be counted and recorded. What is the population? What is the sample?

Answer 1

We are selecting 20 sentences from a single book. Hence the sample is those 20 sentences.

Also, sampling is done from a single book, so the population is all the sentences printed in that book.

It might be confusing to some people that the number of words is counted so they must be sample and all words in book should be population. But on looking carefully, we are given the number of selected sentences too, that also indicate this to be the sample. Counting of words in sentences may be for purposes such as the average number of words in a sentence or number of words starting with a vowel in a sentence etc.

This is similar to sampling a group of people(Sentences) from population and measure their statistics like height, weight, temperature etc.(no. of words) to estimate parameters of the population.