Controlling Extraneous Variables

Question 1

How can we control ppt variables?

Answer 1

1. Same ppts in both conditions
2. Match ppts in both conditions based on characteristics
3. Random allocation

Question 2

How does “Same ppts in both conditions” help control evs?

Answer 2

Data for each ppt is compared across both conditions, so prevents characteristics skewing results

Question 3

How does “Match ppts in both conditions based on characteristics” help control evs?

Answer 3

Gives 2 sets of ppts that are as similar as possible

Question 4

How does “Random allocation” help control evs?

Answer 4

Randomly assign ppts to diff conditions - distributes characteristics across conditions

Question 5

How can we control SITUATIONAL variables?

Answer 5

1. Standardised procedure - same across all conditions
2. Counterbalancing
3. Random allocation
4. Single-blind technique
5. Double-blind technique

Question 6

How does counterbalancing prevent sit.v?

Answer 6

1. Prevents order effects

2. Split ppts in 1/2 - one half experience condition A THEN B. the other half vice versa

Question 7

How does random allocation prevent sit.v?

Answer 7

1. Randomly assign ppts to a condition

2. Pretext to counterbalancing; prevents order effects

Question 8

How does a single-blind technique prevent sit.v?

Answer 8

1. Prevents demand characteristics

2. Aims + info of procedures are withheld from ppts

Question 9

How does a double-blind technique prevent sit.v?

Answer 9

1. Prevents demand characteristics ENCOURAGED BY investigator effects
2. Ppts AND researchers involved in data collection/ppt interaction don’t know aims
   • hire an independent researcher