# What is Sampling?

Suppose that you would like to know the average height of the human population. It is impossible to know this because you cannot know the height of every living human being and therefore you cannot calculate its mean. Click here to see the Average Human Height Worldwide. How is it possible to know this information?

Instead of measuring the height of every human being in a given country, we measure the height of a sample taken from that country. If the sample is chosen well, then the sample represents the entire population and any calculations based on the sample can be said for the whole population – this is called **inference**.

# Terminology

Population – …

Census – …

Sample – …

# Methods of Sampling

## Simple Random Sampling

Simple random sampling is a particular kind of random sampling whereby each member has an EQUAL chance of being selected.

## Stratified Sampling

a sampling technique whereby the population is divided into strata according to given criteria and the sample that is chosen preserves the strata proportions.

## Systematic Sampling

a sampling technique where the sampling starting point is chosen randomly and the rest of the sample is chosen periodically thereafter.

## Quota Sampling

similar to stratified sampling but researchers may select the units they require from the given strata.

## Opportunity Sampling

or convenience sampling, is obtained when members from a given population are willing to participate in the investigation, such as a survey.

Once you have taken a sample from a given population, you would then analyse that data you have collected and gather statistics. How you present data and interpret your findings is very important – see Data Representation & Interpretation.