Sampling

Types of sampling Convenience Sampling Quota Sampling Cluster Sampling Systematic Sampling Random Sampling Stratified Sampling

Convenience sampling Is when you stand in one place at a certain time and ask whoever walk past you…who are interested. Its very easy to do and is very cheap. However it can very bias and time consuming. EXAMPLE- a company is researching into different brands of hair gel. The interviewer stands in a supermarkets and asks first 100 people…to answer him… what there best brand is.

Quota Sampling Quota sampling is often used in market research. Its when you stand in one place ask a certain number of people, but the people have to be a certain type. Its very easy to do and is very cheap. However it can very bias and time consuming. EXAMPLE- John is researching favourite breakfast cereals. He asks five men aged 20-30, five men aged 30-40, five women aged and five women aged These 20 people form his quota sampling.

Cluster Sampling The population is devided into smaller groups. Each group is called a cluster. One or more cluster is chosen using random sampling. It is very easy to do However it can be bias. EXAMPLE-if your asking how long students spend on homework. Then your clusters can be tutor groups. Pick 2 or 3 random classes and ask everybody in those groups.

Systematic Sampling Is when you number each person, then pick every, for example, fourth person afterwards. it is very straightforward and very quick. However it can not represent the group evenly.

The table shows the people in a youth club. Lets pick a sample of 10. Each member is given a number. 30(members) 10(sample)=3 So we need to choose every third person. Using random sampling pick a person from 1,2 and 3. lets say you got two. After AJ pik every third person. The names remaining are those which you will choose. EXAMPLE-

Random sampling Is where everybody is chosen at random and has every chance of being chosen. This sampling is not bias at all. However it can give a mis-representation of the data.

EXAMPLE- a tennis club has 40 members. They receive 5 tickets for wimbledon. They want to chose 5 people at random. Firstly each of the forty people will be given a number. Picking the numbers can be done in three ways. Picking numbers out of a hat The random number table The random function button on the calculator.

Stratified Sampling Is random sampling but where you have a fair representation of males/females, age, area e.t.c. This sampling technique is not bias and will represent the sample frame fairly. However it can take a long time.

Example- You are surveying the quality of the school dinners for years 7,8 and 9. Year 7 contain 50 pupils, year 8 contains 75 pupils, whilst year 9 have 64 pupils. You need to pick out a sample of 30. Firstly you need to decide how many pupils from each year to pick. So find the total number of pupils and the fraction of pupils from each year. This means the sample will contain: 8 year 7 pupils 12 year 8 pupils 10 year 9 pupils. To find these pupils you will use random sampling