Lesson 10 research methods sampling and experimental design 2013

Lesson 10: Research Methods

Sampling &

Experimental Design

Monday, 14 January 2013

Lesson 9 Exam Question

2012 VCAA Exam


QuestionA DCB


OUTCOMES:

Define population Define sample

Describe the process of sampling procedures including random, stratified and random stratified

Describe the process of participate allocation to groups (experimental and control) including random allocationDiscuss the advantages and disadvantages of different

experimental designs including repeated measures, matched participants and independent groups

Describe the placebo effect and ways of managing its occurrence

Describe the experimenter effect and ways of managing its occurrence


Sampling is the selection of participants for a research.

Population refers to the group which the research wishes to draw conclusions from.

The term sample refers to the members of the population that have been chosen to take part in the research.

Sampling procedures must ensure that the sample is representative of the population.

Sampling


Representative Samples

Two techniques are used to ensure a representative sample: 1)Random Sampling 2)Stratified Sampling and Stratified Random Sampling.


A sampling procedure in which every member of the population has an equal chance of being selected

Examples include: 1) Picking a name out of a hat 2) Tattslotto 3) Closing my eyes and selecting a number to match that number with student id numbers.

Random Sample


Stratified Sampling and Stratified Random Sampling

Is used when you wish to eliminate the effects of confounding variables.

The effects of a certain variable can be eliminated as a possible confounding variable in an experiment.

The variable could be any personal attribute, such as age, years of education, ethnicity, gender, IQ etc.


Activity:

Stratified Random Sampling


Participant Allocation: Experimental & Control Groups

The experimental method uses two different groups called the experimental and control groups.

The experimental group are exposed to the IV, known as the ‘treatment’.

The control group do not receive the treatment (IV).

The purpose of the experimental group is to show the effects of the IV on the value of the DV.

The purpose of the control group is to form a basis for comparison with the experimental group.


Experimental and Control Group Allocation

It is super important that all participants have an equal chance of being in the experimental or control group. That is Random Allocation.

When there is a large enough sample, both the experimental and control groups will be equivalent on all participant characteristics therefore the presence or absence of the IV is the only difference between them.

E.G. If we had all males in the experimental group and all females in the control group, then an obvious extraneous variable will be gender.


Experimental Designs

There are three popular experimental designs

Repeated Measures Design

Matched Participants Design

Independent Groups Design


Repeated Measures Design (within participants design)

• In a repeated measures design all participants experience both the experimental and control groups.

• This is possible by conducting the experiment on two occasions and then comparing the two results.


What are the advantages of repeated measures design?

What are the limitations (disadvantages)?


Matched Participants Design

• Enables the researcher to identify a variable that is likely confound and to eliminate the effects of this variable from the experiment.

• Participants can be ranked in accordance with their scores on this variable


• For example

• A sports coach developed a new game plan that would help the team reach the playoffs. He decided to test this by giving the experimental group the instruction but not the control group. Because individual skills would be a confounding variable, he decided to ‘match’ the groups. The two highest skilled players will be randomly allocated to either the experimental or control group, the third and fourth most skilled will then be randomly allocated to either and so on and so forth until all players were allocated to a group resulting in the same mean skill percentage in both groups.


What are the advantages of matched participants design?



• Allocates participants to the experimental or control group at random

Independent Groups Design (between participants design)


What are the advantages of independent groups design?



PLACEBO EFFECT

Participants expectations

This may effect the DV resulting in invalid results

Can be eliminated by using single blind procedure, that is participants are unaware of which group they are in.


EXPERIMENTER EFFECT

Experimenter influences

experiment

For example: Experimenter treats participants differently depending on the group they are in which in turn

influences the behaviour of the participant and effects the results

Can be eliminated by using a double blind procedure, that is, neither the experimenter or the participants are aware of whether they are

in the experimental or control group


Lesson 10 research methods sampling and experimental design 2013

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