Do you remember what sampling methods can be used in A2/A-level Biology?
Random Sampling
- In this technique, every member of the total population has an equal chance of being selected and the selection of one member does not affect the probability of selection of another member.
- A sample can be obtained using random numbers.
- This is the most accurate method as it has no bias.
- There are 3 alternative ways of using random numbers to sample areal distributions: random point, random line and random area.
(1) Point – a grid is superimposed over the area of the map to be sampled and points are then identified using random number table and plotted on the map.
(2) Line – random numbers are used to obtain 2 end points which are then joined by a line, which uses the same 8 random points.
(3) Area – areas of constant size are obtained using random numbers.
Systematic Sampling
- This is a sample in which values are selected in a regular way, e.g. choosing every 10th person on a list.
- It can be operated using individual points, lines or areas.
- This is quicker and easier to use, although some bias or selection is involved.
- It may either overstress or miss an underlying pattern.
(1) Point – this can show changes over distance.
(2) Line – may be used to choose a series of equally spaced transects across an area of land.
(3) Area – used for land-use sampling, to show change with distance or through time.
Stratified Sampling
- In this method, the population is divided into categories and sampled within each.
- Once the groups have been determined, they can be sampled either randomly or systematically.
(1) Stratified systematic – very useful, in many situations, e.g. political opinion polls.
(2) Stratified random – can be used to cover a wide range of data, both in interviewing and in fieldwork and map work.
That's the end of the topic!
Drafted by Bonnie (Biology)