L7 - Experimental Designs

Question 1

what is EXPERIMENTAL DESIGN?

Answer 1

the EXPERIMENTAL DESIGN OF A STUDY is how the PARTICIPANTS ARE ASSIGNED TO DIFFERENT CONDITIONS.

There are 3 MAIN TYPES of EXPERIMENTAL DESIGNS:

• INDEPENDENT GROUPS
• REPEATED MEASURES
• MATCHED PAIRS

Question 2

what is the INDEPENDENT GROUPS DESIGN?

Answer 2

in the INDEPENDENT GROUPS DESIGN, DIFFERENT PARTICIPANTS are used in EACH OF THE CONDITIONS, therefore EACH GROUP of pps is INDEPENDENT FROM ONE ANOTHER

Pps are USUALLY RANDOMLY ALLOCATED to EACH CONDITION to BALANCE OUT ANY PARTICIPANT VARIABLES

Question 3

what are the ADVANTAGES of INDEPENDENT GROUPS DESIGN?

Answer 3

1) ORDER EFFECTS WILL NOT OCCUR as there are DIFFERENT PPS IN EACH CONDITION. ORDER EFFECTS are when the SEQUENCE in which pps take part in CONDITIONS INFLUENCES THEIR PERFORMANCE or BEHAVIOUR.
2) the CHANCE OF DEMAND CHARACTERISTICS is REDUCED as pps do ONLY ONE CONDITION each and so have LESS CHANCE TO GUESS THE PURPOSE OF THE STUDY
3) as BOTH GROUPS of pps CAN BE TESTED AT THE SAME TIME, this experimental design SAVES TIME

Question 4

what are the DISADVANTAGES of INDEPENDENT GROUPS DESIGN?

Answer 4

1) MORE PARTICIPANTS ARE NEEDED for this experimental design
2) there is ALWAYS A CHANCE that the DIFFERENT RESULTS BETWEEN THE TWO CONDITIONS are DUE TO PARTICIPANT VARIABLES RATHER THAN MANIPULATION OF THE INDEPENDENT VARIABLE

Question 5

what is a REPEATED MEASURES DESIGN?

Answer 5

in the REPEATED MEASURES DESIGN, each PARTICIPANT IS TESTED IN ALL CONDITIONS OF THE EXPERIMENT

Question 6

what are the ADVANTAGES of REPEATED MEASURES DESIGN?

Answer 6

1) as the SAME PEOPLE are MEASURED IN ALL CONDITIONS there are NO PARTICIPANT VARIABLES BETWEEN THE CONDITIONS - increased validity
2) HALF AS MANY PARTICIPANTS ARE NEEDED when compared to an independent groups design

Question 7

what are the DISADVANTAGES of REPEATED MEASURED DESIGN? - PT 1

Answer 7

1) ORDER EFFECTS MAY AFFECT THE RESULTS - one way to AVOID THIS is COUNTERBALANCING, this is when HALF THE PPS do CONDITION A FIRST and CONDITION B SECOND while the other half do CONDITION B FIRST and then CONDITION A SECOND. COUNTERBALANCING DOES NOT ELIMINATE ORDER EFFECTS, which WILL BE PRESENT because there are TWO SEPARATE TASKS TO BE COMPLETED BY EACH PERSON.

However, COUNTERBALANCING CONTROLS THE IMPACT OF ORDER EFFECTS and allows ORDER EFFECTS to be DISTRIBUTED EVENLY ACROSS BOTH CONDITIONS

Question 8

what are the DISADVANTAGES of REPEATED MEASURED DESIGN? - PT 2

Answer 8

2) DEMAND CHARACTERISTICS are MORE LIKELY TO OCCUR as pps are INVOLVED IN THE ENTIRE STUDY
3) this experimental design TAKES MORE TIME, especially if a TIME GAP BETWEEN DIFFERENT CONDITIONS is required

Question 9

what is a MATCHED PAIRS DESIGN?

Answer 9

in the MATCHED PAIRS DESIGN the different pps are USED IN ALL OF THE CONDITIONS, just as with the INDEPENDENT GROUPS DESIGN

However, pps in the TWO GROUPS are MATCHED ON CHARACTERISTICS IMPORTANT FOR THAT STUDY (e.g age, gender, IQ). IDENTICAL TWINS are often USED IN MATCHED PAIRS DESIGNS

Question 10

what are the ADVANTAGES of MATCHED PAIRS DESIGN?

Answer 10

1) there is LESS RISK OF ORDER EFFECTS
2) there is LESS RISK OF DEMAND CHARACTERISTICS
3) PARTICIPANT VARIABLES are UNLIKELY as the GROUPS HAVE BEEN CLOSELY MATCHED

Question 11

what are the DISADVANTAGES of MATCHED PAIRS DESIGN?

Answer 11

1) TWICE AS MANY PPS ARE REQUIRED compared with a REPEATED MEASURES DESIGN
2) The MATCHING PROCESS is INCREDIBLY DIFFICULT; even TWO CLOSELY MATCHED INDIVIDUALS will have DIFFERENT TRAITS which can act as EXTRANEOUS VARIABLES
3) the MATCHING PROCESS is INCREDIBLY TIME CONSUMING