Sampling Advantages and Disadvantages

Question 1

Random Sampling

Answer 1

Assign a number to every member of the population. Use a random selection method to pick a number. Ignore repeats.

Advantages - Representative (everyone has equal chance to be picked)
Unbiased

Disadvantages - Needs a full list of population.
Not always convenient as it can be time consuming and expensive.
Needs a large sample.

Question 2

Stratified Sampling

Answer 2

Split the population into groups.
Use formula sample = strata/total x sample size.
Use random sampling within strata.

Advantages - Sample is in proportion to population
Best used for populations with groups of equal sizes (such as school year groups)

Disadvantages - Time consuming

Question 3

Systematic Sampling

Answer 3

Divide your population size by sample size to calculate intervals (e.g. 400/40 = 10 so split into 10s)
Use random sampling to generate a starting point. e.g. 7
select every 10th item AFTER the 7th person. So 7th, 17th, 27th etc

Advantages - population is evenly sampled
Can be carried out by machine
Sample is easy to select

Disadvantages - not strictly random as some members cannot be chosen.

Question 4

Cluster Sampling

Answer 4

Divide the population into natural grups, groups are chosen at random and every member of the group are sampled.

Advantages - economically efficient
Can be representative if lots of small clusters are sampled

Disadvantages - High Sampling error
Clusters may not be representative of the population and may lead to a biased sample

Question 5

Quota Sampling

Answer 5

Group population by characteristics (e.g. gender and age)
Select quota for each group (e.g. 30 men under, 40 women under 30)
Obtain sample by finding members of each group until quota is met

Advantages - quick to use
Cheap
Do not need sample frame or full list of the population

Disadvantages - NOT RANDOM The interviewer is choosing the participants and therefore it is biased. So each person doesn’t have equal chance to be selected.

Question 6

Opportunity Sampling

Answer 6

Using people/items that are available at the time. E.g. Interviewing the first 10 people you see on a Monday morning

Advantages - Quick, cheap and easy

Disadvantages - Not Random - The sample has not be collected fairly so may not be representative of hte population. Every member doesn’t have equal chance to be selected.

Question 7

Judgement Sampling

Answer 7

When researcher uses their own judgement to select a sample, they think will represent the population. E.g. A teacher

Advantages - easy, quick

Disadvantages - NOT RANDOM
Quality of sample depends on the person selecting the sample.