Empirical Analyses of the Factors Affecting Confirmation Bias and the Effects of Confirmation Bias on Software Developer/Tester Performance

Background: During all levels of software testing, the goal should be to fail the code. However, software developers and testers are more likely to choose positive tests rather than negative ones due to the phenomenon called confirmation bias. Confirmation bias is defined as the tendency of people to verify their hypotheses rather than refuting them. In the literature, there are theories about the possible effects of confirmation bias on software development and testing. Due to the tendency towards positive tests, most of the software defects remain undetected, which in turn leads to an increase in software defect density. Aims: In this study, we analyze factors affecting confirmation bias in order to discover methods to circumvent confirmation bias. The factors, we investigate are experience in software development/testing and reasoning skills that can be gained through education. In addition, we analyze the effect of confirmation bias on software developer and tester performance. Method: In order to measure and quantify confirmation bias levels of software developers/testers, we prepared pen-and-paper and interactive tests based on two tasks from cognitive psychology literature. These tests were conducted on the 36 employees of a large scale telecommunication company in Europe as well as 28 graduate computer engineering students of Bogazici University, resulting in a total of 64 subjects. We evaluated the outcomes of these tests using the metrics we proposed in addition to some basic methods which we inherited from the cognitive psychology literature. Results: Results showed that regardless of experience in software development/testing, abilities such as logical reasoning and strategic hypotheses testing are differentiating factors in low confirmation bias levels. Moreover, the results of the analysis to investigate the relationship between code defect density and confirmation bias levels of software developers and testers showed that there is a direct correlation between confirmation bias and defect proneness of the code. Conclusions: Our findings show that having strong logical reasoning and hypothesis testing skills are differentiating factors in the software developer/tester performance in terms of defect rates. We recommend that companies should focus on improving logical reasoning and hypothesis testing skills of their employees by designing training programs. As future work, we plan to replicate this study in other software development companies. Moreover, we will use confirmation bias metrics in addition to product and process metrics in for software defect prediction. We believe that confirmation bias metrics would improve the prediction performance of learning based defect prediction models which we have been building over a decade