Evaluating the causal mechanisms from procedural justice to police legitimacy and compliance in the United States: An in-depth mixed-methods approach

Procedural justice theory states that when police treat people in a fair, respectful, and neutral manner, individuals are more likely to perceive the police as legitimate and obey the law. To test this perspective, researchers often use experimental vignettes that depict police–citizen interactions and measure subsequent attitudes. However, it is not straightforward to determine causal effects from these designs, as one must assess whether the effect runs only through the intended theoretical pathways. This paper advances beyond “traditional” experimental designs to evaluate the mechanisms linking police–citizen interactions, attitudes, and behavioral intentions. The data consist of a representative sample of 2003 adults residing in the United States. We use a mixed-methods approach combining a pre-registered 3 × 2 × 2 experimental vignette depicting a traffic stop by police with follow-up closed- and open-ended questions, allowing respondents to explain their reasoning. We found that the quality of treatment was statistically related to subsequent perceptions of police legitimacy, but not compliance. However, follow-up placebo tests and open-text responses revealed several issues limiting the strength of causal and theoretical claims. Research using (quasi-)experimental designs should not rely only on statistical significance and should incorporate methods that can better assess intermediate processes and causal assumptions more rigorously when theory testing.