Definition of Causal Claims: A causal claim is the strongest assertion in scientific research. It replaces association verbs (such as related to, associated with, or linked to) with definitive action verbs (such as makes, influences, or affects).
Interventions and Treatments: Causal claims directly inform real-world interventions, treatments, and policy decisions. Valid interventions must be rooted in empirical experimental designs.
Definition of an Experiment: In psychological science, an experiment specifically refers to a study design where researchers manipulate at least one variable and measure another. Experiments are the exclusive methodology capable of establishing causation.
Exemplar Simple Experiments
Example 1: Publicizing Social Norms
Theoretical Rationale: Social norms represent common beliefs and standards of behavior within a group. Because norms exert strong behavioral control (guiding attire, speech, and consumption), publicizing prevalent pro-diversity social norms can foster an inclusive climate.
Researchers surveyed a representative sample of University of Wisconsin (UW) Madison students regarding the statement: "We embrace diversity and welcome people from all backgrounds into our UW-Madison community."
A total of 93% of surveyed students agreed with the statement.
A total of 84% agreed to have their photograph displayed on a poster carrying this message.
Independent Variable Manipulation: Participants were recruited to a laboratory waiting room. The waiting room displayed either:
A Norms Poster displaying the pro-diversity message alongside the survey statistics (93% agreement; 84% photo consent).
A Flu Shot Poster (control condition).
Control Procedures: Participants spent 5minutes to 7minutes in the waiting room and were instructed to leave backpacks and cell phones in a separate room to ensure attention to the posters.
Dependent Variable Measurement: Participants moved to a new testing room, completed a filler memory task, and filled out an attitude survey. The survey assessed attitudes toward outgroup members, motivation to avoid prejudice, and feelings of campus belonging. Responses were aggregated into a composite score representing "inclusive climate."
Results & Replications:
Students exposed to the norms poster scored significantly higher on the inclusive climate measure than those exposed to the flu shot poster (d=0.37, 95% CI [0.04,0.71], p<.05).
Murrar et al. (2020) conducted four follow-up experiments: one tested norms posters in undergraduate classrooms, and three tested a norms video intervention. All four replications demonstrated that communicating pro-diversity social norms caused significantly higher inclusive climate scores.
Example 2: Motivating Infant Perseverance
Theoretical Rationale (Leonard et al., 2017): Investigated whether infants learn the value of persistence by observing adult models exerting effort.
Sample & Setting: Recruited over 100 infants aged 13months to 18months at the Boston Children's Museum play lab. Parents sat adjacent to infants but were instructed not to assist.
Experimental Conditions (Manipulated via Coin Flip):
Effort Condition: Infants observed a female model attempt to remove a toy frog from a plastic box while verbalizing effort ("How do I get this out?"). After multiple attempts, she succeeded ("I got it out!"). She then attempted to detach a toy from a carabiner ("How do I get this off?"), succeeding after repeated tries ("Yay!"). Demonstration duration was exactly 30seconds per toy.
No-Effort Condition: The model used the identical toys for the exact same duration (30seconds per toy) but easily extracted the frog three times in rapid succession and easily unhooked the carabiner toy three times in rapid succession.
Dependent Variable Measurement:
Infants were given a novel, cube-shaped musical toy containing a prominent white button. The button was inert and did not play music.