1.3 Non-random Sampling

Question 1

What is a quota

Answer 1

Population divided into groups according to characteristics

A quota of items in each group is set to try & reflect the group’s proportion in the whole population (quotas are calculated in same way as stratified sampling)

Interviewer selects the actual sampling units until the quotas are reached
(once a quota is full, ignore subsequent sampling units that also meet the characteristic)

Question 2

Advantage of a quota

Answer 2

• Allows the sample to be representative of population
• No sampling frame required, which can be difficult or impossible to obtain in some situations
• Relatively quick, easy & inexpensive to administer

Question 3

Disadvantages of a quota

Answer 3

• Non-random so likely to be biased
• Population must be divided into groups, which can be costly or inaccurate
• Can depend on knowledge/expertise of researcher

Question 4

What is opportunity/convenience sampling

Answer 4

Participants are selected based on thier availability & accessibility to the researcher. In this method, the researcher chooses individuals who are available at the time, rather than selecting them at random or based on any specific characteristics of the population

eg. researcher might choose participants walking by in a public space or students in particular class

Question 5

Advantage of opportunity sampling

Answer 5

• No sampling frame required, which can be difficult or impossible to obtain in some situations
• Easy & inexpensive to administer

Question 6

Disadvantages of opportunity sampling

Answer 6

• Non-random so likely to be biased
• Unlikely to provide a representative sample
• Highly dependent on individual researcher

Question 7

Full marks layout for quota questions

Answer 7

• Add up all elements to create total pop ___ + ___ + ___ = P
• 1st element/P all multiplied by sample asked for
  repeat for all elements
• The researcher selects and [context of Q] the [items] until the quotas of ___ [trout eg], ___ [bass], ___ [pike] have been filled. Ignore any subsequent [items] once a quota is full