RM L5: Experimental design -

Question 1

What is experimental design?

Lesson 5

Answer 1

• How ppts are allocated to varying conditions of the experiment
• Choice of deisgn may increase / decrease validity -> depends on the topic being studied and procedures used
• May be practical factors that force researcher to use a particular design

Question 2

What is independent measures?

Lesson 5

Answer 2

• When ppt only takes part in one level of IV
• If IV is natrually occuring (gender / age) researchers must use this type of design
• In true independent measures ppts are randomly allocated to one level of IV (so they get an equal chance of being placed in any level of IV)
• Uses different ppts for each condition of the experiment
• Experimental grp is exposed to IV control group is not
• Ppts randomly assigned to either condition to reduce impact of ppts variables

Question 3

What are the 2 strengths of Independent Measures?

Lesson 5

Answer 3

1. As ppts only take part in 1 condition they are less likely to guess aim of study reduces chance of demand charecterisitics
2. As ppts only take part in one condition there are no order effects which can reduce validity of study

(when ppts responses in various conditions are affected by order of conditions they are exposed to)

Question 4

What are the 2 weaknesses of Independent Measures?

Lesson 5

Answer 4

1. More ppts are required for this type of design
2. Problem of ppts variables affecting DV rather than IV

(Even by chance all ppl of a certain personality might form one condition and all ppl with different personality may form other condition this mean it could be personality affecting DV not IV)

Question 5

What is a matched pairs design?

Lesson 5

Answer 5

• When ppts are matched on a variable that researchers wish to control in study (gender, age, ethnicity)
• Identical twins (monozygotic) as many variables are already matched
• Once ppt matched each ppt takes part in one level of IV
• Each ppt in exp. group will be matched with ppt in control group
• 1 in exp grp + 1 in control grp
• Overcomes problems of ppts variables + order effects

Question 6

What are the 2 strengths of matched pairs design?

Lesson 5

Answer 6

1. Ppt variables are controlled + eliminated as ppt been matched
2. Researchers can be more confident that IV is affecting DV rather than ppt variables

Question 7

What are 2 weaknesses of matched pairs design?

Lesson 5

Answer 7

1. Time consuming to find ppts and match them up
2. May be a few ppt variables that are overlooked in initial matching these can affect DV rather than IV (we cannot control every ppt variable)

Question 8

What is repeated measures design?

Lesson 5

Answer 8

• Using the same ppts in each condition of experiment
• Ppt variables cannot affect validity
• We can use counterbalancing
• Group 1: A, B
• Group 2: B , A

Question 9

What are the 2 strengths of repeated measures?

Lesson 5

Answer 9

1. Eliminates effect of ppts variables -> as all ppts take part in all conditions so they are controlled
2. Less ppts needed for this design compared to independent measures

Question 10

What are 5 weaknesses of repeated measures?

Lesson 5

Answer 10

1. As ppts take part in all conditions chance of demand charecteristics affecting study -> ppts may work out aim of study and behave differently
2. Order effects can affect the findings -> reduced validity
3. Practise effect: ppts get better at asks when do similiar one or repeat the same one
4. Fatigue effects: More tasks ppts do -> more tired they become
5. Boredom effect: Repeating similar tasks can bore ppts