# Sampling

## Sampling Revision

**Sampling**

**Sampling** is a technique where instead of taking data from the whole **population**, we take data from a small percentage of the population. This can be then used to make **conclusions** on the whole population.

**Random Sampling**

**Sampling** is a useful technique when you need information from a large **population**. It is not efficient and sometimes impossible to take data from every single organism in a **population**, and so **sampling** is a useful approach.

It is vital that sampling is **random**. The data from the sample will be used to make conclusions about the overall population, so the sample cannot have any bias.

**Sampling an Area**

Sometimes you might need to sample parts of an area, rather than looking at the entire thing. For example, you might want to look at the **population size** of daisies in a field.

The most fair and non-biased way to do this is to grid out your area into smaller segments. Label these segments and use a **random number generator** to generate coordinates, from which you will take your samples.

More information about using quadrats and transects in sampling can be found **here.**

**Sampling a Population**

Say you wanted to find out some information about the population of your town, perhaps what shoe size they are. It would be **inefficient** and **time-consuming** to ask every single person in the UK what shoe size they are. Therefore we could pick a smaller **sample** size of this **population**, and ask them.

It is again vital that this sampling is completely **random**, to ensure there is **no bias** when selecting the sample.

**Sampling **is often used for **healthcare **purposes, like research into genetic diseases for example. It can also be used to select people for drug testing. More information about drug testing can be found **here**.

## Sampling Example Questions

**Question 1**: Why must a sample be random?

**[1 mark]**

A sample must be random because this **eliminates any bias**.

**Question 2:** Describe a method that could be used to take samples from an area.

**[2 marks]**

The area should be **gridded out with coordinates**, and then a **random number generator** should be used to make some coordinates for the samples.

**Question 3: **A student wants to sample a field to help estimate the size of the daisy population. State what is wrong with the following sampling set up, and give one reason why. The areas the student has chosen to sample are in blue.

**[2 marks]**

The samples are all **close to each other**.

This might be because the student **hasn’t used a random number generator**.