Observe Develop Theory/ Hypothesis

Test Collect & Conclude

Lesson 9 –

Understand issues with sampling and generalisability.

Sampling Techniques

People in Ruislip High Street are approached to take part in a study

on shopping behaviour.

An poster in placed in the library asking for students to take part in

a memory study.

A researcher visits a day care centre and asks parents to help

with an investigation into the effects of day care.

A psychologist uses his research methods class students to fill out a questionnaire on their revision

habits.

Mr Griffin uses some of his psychology class for a study and selects them using his powerpoint

name selector.

A psychologist researches year 7 Ruislip High school students. He chooses 50 by cutting up names

from the register and picking them from a hat.

A researcher visits a day care centre and asks parents to help

with an investigation into the effects of day care.

A researcher conducts a study in a business with 100 workers. He

has 50 short straws and 50 longer straws. He asks them all to select

one…. Those who select the short straws

take part in the study.

• General Population = Everyone• Target population = people the research is interested in• E.g. males• E.g. children who go to day care

• Sample – those from the target population who take part in the study• Sampling technique – how the sample was chosen: random, opportunity, or

volunteer Is the sample Representative?

• General Population = everyone

• Target population = people we are are interested in

• Sample = who from the target population you test/observe/give questionnaire to

• Sampling technique = how you get the sample

• But does that sample represent the target population?

Observe Develop Theory/ Hypothesis

Test Collect & Conclude

Recap

Sampling Techniques

Random

Equal chance so unbiased.

More representative

Often not possible.

Quick, easy, more practical

Sample influenced by where people asked- generally unrepresentative

More varied sample.

Volunteer bias (e.g. more motivated). May not be typical of the target population- unrepresentative

• Identify the sampling technique used in this study (1 mark)

• Explain one strength and one weakness of using this technique in this study (2 + 2 marks).

– ‘in this context’– ‘for the researchers’– ‘in this investigation’

• One strength of this technique is…. (knowledge)• In this study…. (application)

• One weakness of this technique is…. (knowledge)• In this study…. (application)

Exam technique

Task:

1. Sampling technique?

2. One strength/ weakness is….

3. In this situation….

Task:

1. Sampling technique?

2. One strength/ weakness is….

3. In this situation….

• Random technique, + and –• Opportunity technique, + and –• Volunterre technique, + and –

Observe Develop Theory/ Hypothesis

Test Collect & Conclude

Sample Revision

1. Advert in a newspaper

2. Sample bias - the eventual pp’s may be more motivated which is why they signed up

3. Narrow sample – depending on where

people are asked.

4. Often not practical/possible

5. Go to a day care centre and ask for

pp’s

6. More varied sample as can reach more

people.

7. Unbiased sample due to equal chance

of being selected.

8. Quick/easy and practical

9. Pick names out of a hat