Observe

1
Sampling Techniques
Lesson 9 Understand issues with sampling and
generalisability.
Observe
Develop Theory/ Hypothesis
Test
Collect Conclude
2
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.
3
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.
4

• 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

5
Recap

• 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
6
Sampling Techniques
Random
Equal chance so unbiased. More representative
More varied sample.
Quick, easy, more practical
Volunteer bias (e.g. more motivated). May not be
typical of the target population- unrepresentative
Sample influenced by where people asked-
generally unrepresentative
Often not possible.
7
Exam technique

• 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)

• Task
• Sampling technique?
• One strength/ weakness is.
• In this situation.

8
Sample Revision
1. Advert in a newspaper 2. Sample bias - the eventual pps 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 pps 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

• Random technique, and
• Opportunity technique, and
• Volunterre technique, and

Observe
Develop Theory/ Hypothesis
Test
Collect Conclude