A population consists of all the items that is being considered. That is, every item is considered.

A census is a survey of all the items in the population. That is, every item in the population is surveyed.

A sample is a survey of part of the population.

In a random sample, each item in the population has an equal chance of being selected for inclusion in the survey.


1. The table below shows the number of students in each year group.

Year GroupNumber
Year 7240
Year 7240
Year 8252
Year 9235
Year 10225
Year 11240
Year 12165
Year 13155

A survey is taken of the students in Year 11. If 20% of these students need to be sampled, how many students should be included in the survey?

Answer: 48

Select the Year 11 group of 240 students. 240 x 20% = 48 students.

2. A survey is to be taken of the students in the school, above. The survey interviews 20 students outside the Sixth Form Common Room. Indicate two issues with the survey.

Answer: 1. Interviews are likely to pick up too many sixth-formers because of where it takes place.

2. 20 students out of 1752 is not a sample of a reasonable size.