research methods: lab and field experiments to assess EWT

Question 1

laboratory experiments description

Answer 1

• the IV is manipulated and DV is measured
• carried out in a controlled setting
• there are controls over extraneous variables
• usually involve an artificial task
• cause and effect conclusions can be drawn

Question 2

what are the strengths of lab experiments?

Answer 2

• lab experiments are replicable because of strong controls, so they are testable for reliability
• lab experiments use scientific methodology, e.g. forming hypothesis from theory, manipulating IV and measuring DV

Question 3

what are the weaknesses of lab experiments?

Answer 3

• lab experiments are not ecologically valid, because they do not take place in the ppts’ natural setting
• lab experiments may lack validity with regard to the task - e.g. watching car accident on film is not same as witnessing it in real life

Question 4

what is a study that can illustrate lab experiments used to assess EW effectiveness?

Answer 4

• Loftus & Palmer 1974

Question 5

what was the aim of Loftus & Palmer 1974?

Answer 5

• to investigate how information provided to witness after event will influence their memory of that event (e.g. leading questions)

Question 6

what was the procedure of Loftus & Palmer 1974?

Answer 6

• two lab experiments
• independent measures design
• IV = verb used
• DV = estimate of speed or whether ppts saw glass

Question 7

what was method 1 of Loftus & Palmer 1974?

Answer 7

• 45 student ppts were shown short video clips
• they were split into 5 groups, with 9 ppts in each one
• all ppts were asked:
  ‘about how fast were the cars going when they ____ each other’
• each group was given different verb to fill in blank. IV was verb used, which were ’smashed, collided, bumped, hit or contacted’

Question 8

what were results 1 of Loftus & Palmer 1974? (verb - mean estimate of speed (mph))

Answer 8

smashed - 40.8 mph
collided - 39.3 mph
bumped - 38.1 mph
hit - 34.0 mph
contacted - 31.8 mph

Question 9

what was method 2 of Loftus & Palmer 1974?

Answer 9

• 150 student ppts were shown short film that showed multi-vehicle car accident and then they were asked questions about it
• ppts were split into 3 groups (with 50 in each group)
• one group was asked:
  ’how fast were the cars going when they hit each other?’
• second was asked:
  ’how fast were the cars going when they smashed into each other?’
• third group was not asked about speed of vehicles
• one week later, all ppts returned and were asked:
  ’did you see any broken glass?’
  there was no broken glass in the film

Question 10

what were results 2 for Loftus & Palmer 1974? (response - smashed - hit - control)

Answer 10

yes - 16 - 7 - 6
no - 34 - 43 - 44

Question 11

what are the conclusions for Loftus & Palmer 1974?

Answer 11

• as can be seen from results, leading questions can affect speed estimate and also has an effect on whether broken glass is recalled
• Loftus & Palmer argued that verb ’smashed’ meant event was remembered as more severe and so ppts were more likely to report seeing broken glass as this fits with their modified image of event

Question 12

field experiments description

Answer 12

• similar to lab experiments
• IV is manipulated and DV is measured
• there are controls over extraneous variables
• usually involve artificial task
• cause and effect conclusions can be drawn
• take place in natural setting environment of ppt e.g. in public place such as street (difference to lab experiments)

Question 13

what are the strengths of field experiments?

Answer 13

• field experiments are replicable to an extent because of strong controls, so they are testable for reliability
• field experiments are ecologically valid, because they take place in ppts’ natural setting

Question 14

what are the weaknesses of field experiments?

Answer 14

• field experiments might not allow enough control over variables to be reliable because setting is not controlled as it is in lab experiment
• field experiments might not be valid with regards to task either; e.g., line-up that has been set up is not the same as identifying real-life criminal

Question 15

what is a study that can illustrate field experiments to assess EW effectiveness?

Answer 15

• Yarmey 2004

Question 16

what was the aim of Yarmey 2004?

Answer 16

• to test eyewitness recall and ability to identify target person from photographic line-up in field experiment

Question 17

what were the conditions of Yarmey 2004?

Answer 17

• preparation - some ppts were told to be prepared for memory test by female target herself and some were not
• ppts were tested immediately or 4 hours later
• also ppts were told whether target female was present or not in a line-up

Question 18

what was the procedure of Yarmey 2004?

Answer 18

• ppts approached by target female in public place and asked to help look for lost jewellery or **asked for directions*(
• after 2 mins, female researcher went up to ppt and asked them to take part in study - either asked then and there or 4 hours later
• witnesses given questionnaire with 16 items
• then given 6 photos and asked to identify target female (in half cases female was absent and half she was present) ppts were told she may be in the set of photos
• ppts were debriefed

Question 19

what were the results of Yarmey 2004?

Answer 19

• when target was present in photo line-up there was 49% correct identification (students predicted 63%)
• 62% correctly said she was not there in ‘target absent’ condition (students predicted 47%)
• ppts who were told their memory would be tested were better at recall but not at photo identification
• age estimates was reasonably accurate - better than height or weight

Question 20

what was the conclusion of Yarmey 2004?

Answer 20

• witness preparation did not improve eye-witness identification and students significantly overestimated how many witnesses would be able to identify target correctly - an indication of why jurors put great faith in eyewitnesses during a court case