Testing the Accuracy of Eyewitness Testimony
AbstractThink back to the last time you went to the grocery store. How well can you describe the person who was ahead of you in the check-out line? How many details do you remember about the person? How accurate do you think your memory is? Here is a project to investigate the accuracy of people's observations during everyday life.
Andrew Olson, Ph.D., Science Buddies
The idea for this project is from:
- Giles, R.A.B., 2003. Seeing Is Believing . . . Or Is It? California State Science Fair Abstract. Retrieved July 27, 2006.
The purpose of this project is to determine whether eyewitness reports are reliable enough to be used as substantial evidence in criminal convictions, by examining whether gender, distance from subject, and delay in recollection time affect the accuracy of reporting.
Eyewitness accounts are continuously put into question in the court room. By studying how memory works and what factors influence what we remember, we can try to determine how credible eyewitness accounts are and if they are an accurate source of evidence in crimes.
Psychologists typically divide the process of remembering into three stages: encoding, storage, and retrieval. Encoding encompasses the initial perception of the event. Storage is making a lasting record of the perception. Retrieval is recalling the event in response to some cue or query. As you will see in your background research (and perhaps in your own experiment), the process of recall is not like replaying a video disc. Many factors can influence how events are recalled, including the time that has elapsed between storage and retrieval. See the Variations section for other possible avenues of exploration.
In this project, you will compare the accuracy of eyewitness accounts of an event when subjects are questioned immediately after the event vs. one day later. This project requires staging an event (it can be as simple as having a visitor interrupt a class to ask the teacher a question), and then conducting a written survey to measure how accurately your eyewitnesses recall the event (e.g., the appearance of the visitor, the sequence of the interaction with the teacher, etc.). You will have to prepare the survey, and analyze the results.
Refer to the Science Buddies resource, Designing a Question-Based Study, for guidance in designing your survey. The Science Buddies resource, How Many Survey Participants Do I Need?, will show you how to figure out how many respondents you need to recruit in order to achieve your desired level of confidence that your results are representative of the total population.
There are special considerations when designing an experiment involving human subjects (the eyewitnesses, in this project). ISEF-affiliated fairs often require an Informed Consent Form for every participant who is questioned. In all cases, the experimental design must be approved by a scientific review board prior to the commencement of experiments or surveys. Please refer to the Science Buddies page Projects Involving Human Subjects for additional important requirements.
Terms and Concepts
To do this project, you should do research that enables you to understand the following terms and concepts:
- forgetting curve,
- false memory,
- misinformation effect.
- What are the differences between short-term memory, long-term memory, and working memory?
- What are some of the possible effects that questioning can have on memory recall?
- The Wikipedia article on human memory is a good place to start, and also has many suggestions for further reading:
Wikipedia Contributors. (2014, December 16). Memory. Wikipedia: The Free Encylopedia. Retrieved December 17, 2014.
- The Innocence Project. (n.d.). Reevaluating Lineups: Why Witnesses Make Mistakes and How to Reduce the Chance of a Misidentification. Retrieved December 17, 2014.
- Campbell, T.W. (2005). Issues in Forensic Psychology: Eyewitness Recall. Retrieved July 27, 2006.
Materials and Equipment
To do this experiment you will need the following materials and equipment:
- sample group to serve as witnesses,
- a person unfamiliar to the sample group to act out scenario,
- Optional: video camera and tripod to record the scenario.
Working with Human Test Subjects
There are special considerations when designing an experiment involving human subjects. Fairs affiliated with Intel International Science and Engineering Fair (ISEF) often require an Informed Consent Form (permission sheet) for every participant who is questioned. Consult the rules and regulations of the science fair that you are entering, prior to performing experiments or surveys. Please refer to the Science Buddies documents Projects Involving Human Subjects and Scientific Review Committee for additional important requirements. If you are working with minors, you must get advance permission from the children's parents or guardians (and teachers if you are performing the test while they are in school) to make sure that it is all right for the children to participate in the science fair project. Here are suggested guidelines for obtaining permission for working with minors:
- Write a clear description of your science fair project, what you are studying, and what you hope to learn. Include how the child will be tested. Include a paragraph where you get a parent's or guardian's and/or teacher's signature.
- Print out as many copies as you need for each child you will be surveying.
- Pass out the permission sheet to the children or to the teachers of the children to give to the parents. You must have permission for all the children in order to be able to use them as test subjects.
Staging the Event
- Arrange to have a person (who is unfamiliar to the class) knock on the door, enter the class, interact with the teacher briefly, and then leave. You can think of your own scenarios, but some possible ideas are:
- flower delivery,
- asking a question,
- express package delivery.
- The survey should probe how accurately the students remember the event. Here are some ideas for questions to get you started (assuming a delivery person scenario):
- At what time did the delivery person enter the room?
- How long was the delivery person in the room?
- What did the delivery person bring?
- Did the delivery person leave anything behind?
- Did the delivery person take anything from the room?
- What did the delivery person say to the teacher?
- Please describe the delivery person, including as much of the following information as you can accurately remember: height, weight, skin color, hair color, eye color, clothing, distinguishing features.
- Note: the students should also fill out the time and date that the survey was completed, and the surveys should be anonymous.
- After the visitor leaves, give the students in the class sealed envelopes containing the survey. Half of the envelopes (and surveys) should be marked "complete now" and half should be marked "complete tomorrow."
- Have the students return the completed surveys to the teacher.
Analyzing the Results
- If you record the event, use your recording to double-check your own recall of the event before grading the surveys!
- For each component of the description, analyze the percentage of correct responses. Which components of the description were correctly observed most often? Which were correctly observed least often? Does the "average" response provide an accurate description of the subject?
- For numeric data, calculate the average, median, and standard deviation of the responses. A histogram showing the distribution of responses would be a good way to examine this data. How close is the average response to the actual number?
- For analyzing eyewitness accuracy of what was said, one idea would be to devise a rating scale for responses, perhaps something like this:
- 0 = no response
- 1 = inaccurate wording which changed the sense of what was said,
- 2 = accurately described sense of what was said, but not exact wording,
- 3 = accurately described wording
- The students who participate in the experiment might be interested to see the recording after they have completed their surveys. How many were surprised to find that they had made mistakes?
Ask an Expert
- Have test subjects view a scene from a film and then ask questions about recall of the scene. For example, you could select a scene depicting an automobile accident.
- Test the effect of misleading questions on later recall. Separate your "witnesses" into two groups. For one group, ask a question about something that was not in the scene (e.g., a building or landmark not in the scene, or a character that was not present). Survey both groups about the accident scene at a later time (e.g., between 1–7 days later). Does the group exposed to the misleading question incorporate inaccurate information into their recall of the event? If so, how prevalent is the effect?
- Test the effect of wording on immediate recall. Separate your "witnesses" into two groups. For one group, ask a question such as, "How fast were the cars moving when they smashed?" For the second group, change the wording to something like, "How fast were the cars moving when they collided?" Does the average speed reported by each group differ?
- Test the effect of distractions during screening on recall. Separate your "witnesses" into two groups. Give each group identical instructions: they are going to watch a scene from a movie, and that they should try to remember every detail about the scene. For one group, the movie is shown uninterrupted. For the other group, have someone enter the room during the screening (e.g., to quietly bring a note to the teacher's desk and then leave the room). How do the two groups differ in the accuracy of their recall? Are they equally accurate for the portion of the scene before the distracting event occurred? During the distracting event? Following the distracting event?
- Design an experiment to test the effect of longer delays on recall.
- For another experiment related to forensic psychology, see the Science Buddies project Testing for Bias in a Photo Lineup.
If you like this project, you might enjoy exploring these related careers: