Experimental designs

Question 1

Independent Groups

Answer 1

Involves using different people for each condition.

E.g. Group A is the experimental group taking the drug and group B is the placebo group.

Question 2

Repeated Groups

Answer 2

Using the same people in each condition.

E.g. group A takes drug and group A takes placebo

A major probelm with this is that the second time around, Pt’s in a group will simply perform better due to practice and order effects (this would happen regardless of whether they have the drug). This means order and effects are an extraneous variable.

Question 3

Overcoming order effects?

Answer 3

Counter-balancing is where the groupof pt’s are split into two and perfrom the tasks in a different order. This ensures that each condition is tested first or second in equal amounts. This ensures that any differences are balanced out.

Question 4

Matched Pairs

Answer 4

Where Pt’s are ‘matched’ or paired with another who is similar in a number of varibles. Each person from a pair goes in different conditions.

E.g. Suppose you’re still investigating the effects of the new drug aiding memory. You will have participants in one group who closely match pt’s in the other on variables such as: age, sex, gender etc. You decide to use identical twins as their DNA matches.

Question 5

Independent evaluation strengths

Answer 5

Completely avoids practice and order effects becuase pt’s are only taking part in one condition, meaning fatigue and boredom are less likely to be an issue.

Can be quick and easy to set up as you simply get one group of pt’s to complete one half of the study ad another group to complete the other half. In theory, this is the easiest design the complete.

Question 6

Indepenent evaluation weaknesses

Answer 6

Needs lots of pt’s as you will require a decent number in each group, double the amount needed in repeated measures. This can prove taxing with time and resources.

There maybe some pt variability i.e. some pt’s in one group may simply be ‘better’ at experimental tasks than pt’s in the other group. This means the comparison between experimental groups could be effected by individual differnences.