Types of sampling

Types of sampling

1. simple random sampling:

   • Every item in the population has an equal chance of being chosen you could assign a number to each item and then use random number tables, a calculator or computer to choose a random sample. ignoring duplicate numbers. you could also pull names from a hat.
   • The method is more suited to a relatively small populations where a complete list of the population to chose a sample from, exists.

2. Systematic sampling:

   • A regular pattern is used to choose a sample. Every item is listed, starting point is randomly chosen and then every Nth item is chosen.
   • This is a quicker method to select a (random) sample, but may be unrepresentative if a pattern exists in the list.
   • E.G. male + female class - everyone is put inn alphabetical order and every 6th person is selected starting with the 3rd student
     • every 6th student may be a girl

3. stratified sampling:

   • the population is divided in to categories (strata) by age, gender, social class... and then a random sample is chosen from each category. The size of each sample is in proportion to the size of each category within the population.

4. Quota sampling:

   • The population is divided in t o groups. A given number (quota) is surveyed for each group.
   • This type of sampling is not random but is cheep to carry out and can be done quickly.

5. Convenience sampling:

   • the most convenient sample is chosen which, for s sample size of 60, could be the first 60 people you meet.
   • It is highly likely that this sample would be biased and unrepresentitive

6. Opinion polls;

   • large scale opinion polls often use a combination of cluster + quota sampling
   • the sample size may be large, but is often based on a very small proportion of the population.
   • the criteria of selection of sample could be geographical area, age...
   • E.G. the accurate estimation of general elections for the government
   • A major disadvantage of conclusions drawn from opinion polls is that they change over time.

7. Cluster sampling:

   • the population is divided into groups/clusters. A random sample of clusters is chosen and every item in the cluster is surveyed.
   • a large number of small clusters maximise the chance of the sample being representative.
   • the method is used by biologists to study different plants