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What different groups are there within ISVA

List as many as you can think of

Learning Objectives

Define 4 sampling techniques

Practice 3 of these using Skittles

Evaluate the different sampling techniques

Big Picture

Why bother?

Population

Sample

• Takes too long to study everyone

• Use a sample of the population to represent everyone

• Key word: representative

Expert Input

Stratified

Opportunistic

Different sampling techniques

Random

Volunteer

Student Led

Time to practice some sampling (not tasting…yet)

Red – TeachersGreen - Year 10Yellow – Year 9

Orange – Year 12Purple – Year 11

How to do it?

Follow the instructions on the worksheet

You will need a calculator!

Ask if you need help

Colour Number

Red

Green

Yellow

Orange

Purple

Discussion

What did you find out?

Method Procedure Strength Weakness

Random Sampling

Stratified Sampling

Opportunity Sampling

Volunteer sampling

Copy and complete this table

Sampling procedures: Simple random sampling

• Simple random sampling: E.g. pulling names out of a hat. Though psychologists and sociologists tend to number all the names in the sampling frame, then get a computer to randomly select the numbers. It is better to say this in exam than say names out of a hat.

Strength and weakness Low bias because everone has equal chance of being chosen so you cant

knowingly or unknowingly introduce a bias by eg putting the better looking and perhaps more confident people in 1 condition/group if confidence was a factor in your d.v

Sample can be checked mathematically for any bias - for true random sampling you need a perfect list for your sample frame on

a practical level this is almost impossible to achieve even for people with a huge amount of funding ie even the electoral register is not a perfect list of everyone in the uk.This can cause bias as those missing may be a specific type of people.(eg homeless or those with mental health problems or non comforming types.)

- Even if you have the perfect list once you have made your random choice of participants it is very unlikely that you will get access to everyone you originally choose .(again bias potential as it is particular type of person that refuse to be involved)

Volunteer self selecting

Asking people to volunteer. If questionnaires are sent out by post those returning them would e considered volunteers. Milgram used volunteers and he paid them for their time,

Strengths and weaknesses

Ethically good because people have freely put themselves forward to take part

You are more likely to get full cooperation - Only certain types of people may volunteer and this

is likely to cause a serious bias in the results and limits the generalisability of the findings in certain types of experiments especially those of a social nature

- It may take a long time to get enough volunteers in comparison to an opportunity sample

Opportunity sample

This is when the researcher takes who ever is available. If the researcher asks someone directly to take part and they agree this is an opportunity sample and not a volunteer sample. If a general advert is put out and people put themselves forward then that would be a volunteer sample

Strengths and weaknesses

It is ethical as long as pp given full information of the study they are asked to participate in also the experimenter can judge if the person is likely to be upset an only target suitable participants

A good sized sample can be obtained far more quickly than a volunteer or random sample

- Using only who is available may mean you only have a certain group of people eg mums at home or students who visit the library

- Open to the experimenter choosing a specific group ie people they are confident to approach

: Stratified sampling 400

students

50% male200 males

25% ethnic minority 50 ethnic minority

males

5 ethnic minority

males

75% white 150 white

males

15 white males

50% female200 females

25% ethnic minority 50 ethnic minority

females

5 ethnic minority

75% white150 white females

15 white females

The sampling frame is divided into ‘strata’. A random sample is then taken from each stratum .You generate categories that may be relevant to the nature of the study such as age gender ethnicity and then ensure you have a certain number from each. I t may be a number proportional to the sample frame

Strengths and weaknesses All the relevant groups or strata have at least some

representation Limits the number of participants needed compared with

random sampling to be sure of having some representaion from each group/strata

- The researcher is really unlikely to be aware of every group and sub group so you are attempting the impossible and in doing so may create a bias by missing out key groups and even over representing certain groups that have similarities which is less likely to happen in a random sample

- It is difficult to get a truly representative number for each group and could end up with a bias in terms of proportions

Quiz

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