Sampling

Question 1

What is simple random sampling? What are disadvantages and advantages?

Answer 1

A simple random sample gives each member of the population an equal chance of being chosen.Some advantages of this are it gives everyone a chance to participate it the survey/study. However, it could be biased towards people and doesn’t include everyone.

Question 2

What are the five main sampling methods?

Answer 2

Simple random sampling, systematic sampling, cluster sampling, stratified sampling and quota sampling

Question 3

What is a systematic sampling?

Answer 3

This is a random sampling with a system! From the sampling frame, a starting point is chosen from random, and thereafter at regular intervals. For example suppose you want to sample 8 houses from a street of 120 houses. 120/8=15, so every 15th house is chosen after a random starting point between 1-15. If the random starting point is 11, then the houses selected are 11, 26, 41, 56, 71, 86, 101 and 116.

Question 4

What is a quota sample?

Answer 4

The selection of the sample is made by the interviewer, who has been given quotas to fill from specified subgroups of the population. For example, an interviewer may be told to sample 50 women between the ages of 45-60.

Question 5

What is a cluster sample?

Answer 5

In cluster samples the unit sampled are chosen in clusters, close to one other. Examples are households on the same road, or successive items off the production line. The population is divided into clusters and some of these are chosen at random. Within each cluster units are chosen by simple random sample or some other method. Ideally he clusters chosen should be dissimilar so that the sample is as representative of the population as possible.

Question 6

What is a census? What are he advantages and disadvantages of using one?

Answer 6

A census is when all of the data in the population is taken. For example a census of the entire population of he UK is taken every 10 years.

Advantages- unbiased, accurate, takes account of the whole population

Disadvantages- time consuming, expensive, difficult to ensure whole population is surveyed

Question 7

What is stratified sampling formula and what will it give you?

Answer 7

A stratified sample will give a sample proportional to the size of the strata. We use the formula: sample size/population size(random) x number of people in the group(for each group)

E.g.

Year 7- 50
Year 8 -49
Year 9 -59
Year 10 -45
Year 11-47
            -----
            250
            -----
I want 100 people! 

100/250 x 59=23.6(24) year nines