Jump to main content

Testing for Bias in a Photo Lineup

172 reviews


You may have read about criminal cases where innocent people have been wrongly convicted of a crime. Sometimes, modern DNA analysis techniques have provided the evidence to exonerate these innocent people. In many cases, mistaken identification by eyewitnesses provided strong evidence for the original conviction. How can prosecutors and defense attorneys make sure that photo lineup procedures used to identify criminal suspects are unbiased? This project shows you how to conduct an objective test for bias in a simulated photo lineup.


Areas of Science
Time Required
Long (2-4 weeks)
Material Availability
Specialty items
Low ($20 - $50)
No issues

Andrew Olson, Ph.D., Science Buddies


The procedure used for this project was adapted from:


The goal of this project is to test a photo "lineup" for bias. How can you tell if the "suspect" is being treated fairly?


Eyewitness accounts are continuously put into question in the court room. Photo lineups, from which a witness identifies a suspect in a criminal case, are one of the tools used for corroborating eyewitness accounts. A photo lineup is also designed to protect innocent people from being caught in a criminal investigation. If the witness cannot identify the suspect from a panel of six (or more) photographs, the reliability of their recall of the crime is called into question.

How can a prosecutor show that a photo lineup was fair (unbiased)? How can a defense attorney back up an argument that a photo lineup was biased against her client? This project shows you how to conduct an objective test of the fairness of a photo lineup.

Terms and Concepts

To do this project, you should do research that enables you to understand the following terms and concepts:



  • The Wikipedia article on human memory is a good place to start, and also has many suggestions for further reading:
    Wikipedia contributors, 2006. Human Memory, Wikipedia, The Free Encylopedia. Retrieved July 27, 2006.
  • Campbell, T.W., 2005. Issues in Forensic Psychology: Eyewitness Recall,. Retrieved July 27, 2006.
  • For basic information on lineup construction procedure and evaluating fairness of a lineup, see:
    Staff, 2006. Eyewitness Identification Research Laboratory, University of Texas El Paso. Retrieved July 28, 2006.
  • This project is based on the procedure described in this paper:
    Malpass, R.S., date unknown. A Lineup Evaluation 'Do-It-Yourself Kit' for Attorneys and Law Enforcement, Eyewitness Identification Research Laboratory, University of Texas at El Paso. Retrieved July 28, 2006.
  • Any introductory statistics textbook should contain an explanation of how confidence intervals are calculated. Here is an online source:
    Staff, 1997. Confidence Intervals, Department of Statistics, Yale University. Retrieved July 28, 2006.

Materials and Equipment

To do this experiment you will need the following materials and equipment:

Experimental Procedure

Note: There are special considerations when designing an experiment involving human subjects. 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 the fair's scientific review committee (SRC) prior to the commencement of experiments or surveys. Please refer to the ISEF rules for additional important requirements for studies involving human subjects: https://www.sciencebuddies.org/science-fair-projects/competitions/human-subjects-regulations.

  1. Instruct your witnesses that they will have, e.g., 20 seconds to examine a photograph and that they will then have to write a physical description of the person in the photograph.
  2. Separately for each witness, show photo of "suspect" and get their written description.
  3. Create a composite written description of the "suspect" using features identified in at least two of the written descriptions. This is the written description that your mock witnesses will use to try to identify the "suspect" from a photo lineup.
  4. For each photo lineup you want to test, you will need 5 "filler" photos. Try to predict which of your lineups will be unbiased, and which will be biased.
  5. Number the photos 1–6, so that your witnesses can select the "suspect" by number.
  6. Do the following steps individually with each mock witness:
    1. Have them read the composite written description of the "suspect."
    2. Take the written description away, and then show them the photo lineup.
    3. Ask them to identify the "suspect" (by number) and record the results.
  7. For each lineup, calculate the number of times each photo (1–6) was identified. Divide this number by the total number of choices made. If the "fillers" were chosen perfectly, you'd expect that each photo would have an equal probability of being chosen. That is, each photo would be chosen 1/6th of the time. How do your results compare to the ideal?
  8. You can also calculate the frequency with which the "suspect" was chosen from the lineup, and calculate the probability that this frequency differs from chance. We'll work an example to show you how:
    1. Write down the number of mock witnesses, n, who viewed the photo lineup: 29.
    2. Write down the number of mock witnesses who chose the "suspect": 14.
    3. Write down the number of photos used in the photo lineup: 6.
    4. Calculate the proportion, p, of mock witnesses who chose the "suspect": 14/29 = 0.483.
    5. Calculate the proportion, q, of mock witnesses who chose "fillers": q = 1 − p = 1− 0.483 = 0.517.
    6. Calculate the standard error, s.e., of  p:
      Equation for finding standard error in a data set .
    7. Expected proportion for choosing suspect by chance: 1/n = 1/6 = 0.167.
    8. Critical ratio for difference from chance: (p − chance expectation)/s.e. = 0.483 − 0.167 / 29 = 3.406.
    9. For a 95% confidence interval (i.e., only a 5% chance that the simulated lineup is biased), the critical ratio must be less than 1.96.
    10. For a 99% confidence interval (i.e., only a 1% chance that the simulated lineup is biased), the critical ratio must be less than 2.58.
icon scientific method

Ask an Expert

Do you have specific questions about your science project? Our team of volunteer scientists can help. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot.

Global Connections

The United Nations Sustainable Development Goals (UNSDGs) are a blueprint to achieve a better and more sustainable future for all.
This project explores topics key to Peace, Justice and Strong Institutions: Promote just, peaceful and inclusive societies.


  • Use the same photo lineup, but show it to two groups of mock witnesses. In one case, show the photos one-by-one (sequential photo lineup), in the other case, show all six photos at once (simultaneous photo lineup). Is there any difference in frequencies?
  • Double-blind procedure (person showing photos does not know which is suspect) vs. suggestive feedback (confirmation when witness correctly identifies "filler" photos)
  • For another experiment related to forensic psychology, see the Science Buddies project Testing the Accuracy of Eyewitness Testimony.


If you like this project, you might enjoy exploring these related careers:

Career Profile
Why people take certain actions can often feel like a mystery. Psychologists help solve these mysteries by investigating the physical, cognitive, emotional, or social aspects of human behavior and the human mind. Some psychologists also apply these findings in order to design better products or to help people change their behaviors. Read more
Career Profile
Guilty or not guilty? The fate of the accused in court lies with the evidence gathered at the crime scene. The job of the forensic science technician is to gather evidence and use scientific principles and techniques to make sense of it. It can be a grueling and graphic job, but very rewarding. If you like the idea of using science to help deliver justice, then you should investigate this career. Read more

News Feed on This Topic

, ,

Cite This Page

General citation information is provided here. Be sure to check the formatting, including capitalization, for the method you are using and update your citation, as needed.

MLA Style

Science Buddies Staff. "Testing for Bias in a Photo Lineup." Science Buddies, 20 Nov. 2020, https://www.sciencebuddies.org/science-fair-projects/project-ideas/HumBeh_p015/human-behavior/testing-for-bias-in-a-photo-lineup. Accessed 3 Dec. 2023.

APA Style

Science Buddies Staff. (2020, November 20). Testing for Bias in a Photo Lineup. Retrieved from https://www.sciencebuddies.org/science-fair-projects/project-ideas/HumBeh_p015/human-behavior/testing-for-bias-in-a-photo-lineup

Last edit date: 2020-11-20
Free science fair projects.