Sampling Techniques

What is sampling?

When completing fieldwork it would be ideal is we could sample the full area / population. However, often there is not time to do this. Therefore, data is gathered on a small part of the whole population or area and use it to inform what the full picture is like.

Why sample?

There is not enough time, energy, money, labour/man power, equipment etc to measure every single item or site within the sampling area.

Stratified Sampling

If it’s known that there are different groups or classes in a population, such as different rock types in an area, or different ethnic groups in a city, it is possible to make sure a representative sample is included in a survey. For example, if different rock types are evidence along a coastal stretch then then the area could be divided up into areas of differing geology. In each of these areas a sample could be taken.

 

Systematic Sampling

Using random numbers can be very time consuming. Systematic sampling is much easier and simpler. Systematic sampling involves choosing items at regular intervals e.g. completing a beach transect every 20 metres or interviewing every tenth person.

Random Sampling

Least biased of all techniques

Each member of the population has an equal choice of being selected

Can be obtained by random number tables

Excel has a function to produce a random number:

=RAND()

=INT(250*RAND())+1