Objective To test whether individuals experience cognitive biases whilst searching using information retrieval systems. Biases investigated are anchoring, order, exposure and reinforcement.

Design A retrospective analysis and a prospective experiment were conducted to investigate whether cognitive biases affect the way that documentary evidence is interpreted whilst searching online. The retrospective analysis was conducted on the search and decision behaviors of 75 clinicians (44 doctors, 31 nurses), answering questions for 8 clinical scenarios within 80 minutes in a controlled setting. The prospective study was conducted on 227 undergraduate students, who used the same search engine to answer 2 of 6 randomly assigned consumer health questions.

Measurements Frequencies of correct answers pre- and post- search, and confidence in answers were collected. The impact of reading a document on the final decision was measured by the population likelihood ratio (LR) of the frequency of reading the document and the frequency of obtaining a correct answer. Documents with a LR > 1 were most likely to be associated with a correct answer, and those with a LR < 1 were most likely to be associated with an incorrect answer to a question. Agreement between a subject and the evidence they read was estimated by a concurrence rate, which measured the frequency that subjects' answers agreed with the likelihood ratios of a group of documents, normalized for document order, time exposure or reinforcement through repeated access. Serial position curves were plotted for the relationship between subjects' pre-search confidence, document order, the number of times and length of time a document was accessed, and concurrence with post-search answers. Chi-square analyses tested for the presence of biases, and the Kolmogorov-Smirnov test checked for equality of distribution of evidence in the comparison populations.

Results A person's prior belief (anchoring) has a significant impact on their post-search answer (retrospective: P < 0.001; prospective: P < 0.001). Documents accessed at different positions in a search session (order effect [retrospective: P = 0.76; prospective: P = 0.026]), and documents processed for different lengths of time (exposure effect [retrospective: P = 0.27; prospective: P = 0.0081]) also influenced decision post-search more than expected in the prospective experiment but not in the retrospective analysis. Reinforcement through repeated exposure to a document did not yield statistical differences in decision outcome post-search (retrospective: P = 0.31; prospective: P = 0.81).

Conclusion People may experience anchoring, exposure and order biases while searching for information, and these biases may influence the quality of decision making during and after the use of information retrieval systems.