Sampling Methods

Sampling Methods

1. Random Sampling

   • Every member of a population has an equal chance of being selected. eg. using random number tables.
     • Large population is time consuming as list has to be created.
     • Large sample, best chance of unbiased representative.

2. Stratified Sampling

   • Dividing the target population into important subcategories. Selecting members in proportion that they occur in the population.
     • Sample is representative of the population.
     • Can be time consuming as subcategories have to be created. Usually has to be combined with random sampling.

3. Volunteer Sampling

   • Individuals who have chosen to be involved with the study. eg. responding to an advert.
     • Convenient and ethical if it leads to informed consent.
     • Unrepresentative. eg. daytime advert wont attract full-time workers.

4. Opportunity Sampling

   • Simply selecting those people that are available at the time. eg. in cafes
     • Quick, convenient and economical. Most common type of sampling.
     • Very unrepresentative samples and often biased by the researcher who will unconsciously choose people who are helpful.

5. Systematic Sampling

   • People are selected at fixed intervals from the target population. eg. select every 20th person from a list of 1000 to get a sample of 50.
     • Generally representative. Avoids researcher bias and the biases of volunteer samples.
     • Some people may be excluded if the list is incomplete.

6. Quota Sampling

   • Researcher works out what categories they want to represent - for example might set a quota for the number of boys and the number of girls in your sample for example 40% boys and 60% girls. Then takes an opportunity sample of people who are available, and whenthere is 40% boys stop recruiting males.
     • Helps to ensure small minority groups are represented within a sample.
     • It does not always result in a representative sample as proportions of small groups are distorted. It must be combined with another method.