The experimenter in the experiment
About this app
Self-test after Rosenthal and Fode (1963): you rate twelve runs of rats in an elevated T-maze, supposedly from a bright or a dull strain. The debriefing reveals six identical pairs. Plus the original data (2.32 versus 1.54 correct choices per rat per day), a model with a double-blind switch and Clever Hans from 1904.
With explain mode: an AI tutor walks you through the app, points out what matters in the scene and answers your questions.
The experimenter effect
The expectations of the person running an experiment can change the measurements without them noticing. In 1963 Robert Rosenthal and Kermit Fode gave twelve students five rats each, supposedly from a “maze-bright” or a “maze-dull” strain. The labels were random. Even so, the supposedly bright rats chose the rewarded dark platform of an elevated T-maze more often: on average 2.32 versus 1.54 correct choices per rat per day, and they refused less often (17 versus 43 of 150 sessions each). The experimenters reported handling “bright” rats more and more gently.
What the app shows
In the self-test you are the experimenter: rats run through a T-maze drawn in perspective, and you rate twelve runs as correct, wrong or no choice. Ambiguous moments such as hesitating, turning back or stopping are marked. The debriefing reveals that the runs were six identical pairs with different labels and compares your ratings. Further views show the original curves over five days, a model with a double-blind switch and Clever Hans from 1904 with Wilhelm von Osten and Oskar Pfungst.
Try it yourself
Rate all twelve runs before you open the debriefing, otherwise the experiment is spoiled. Afterwards you can replay each pair: two rats with different labels run the same path. In the model you change the strength of the expectation, separate the paths of handling and scoring and switch to double-blind. With Clever Hans you ask 3 + 2 once with and once without the questioner knowing the answer. Your ratings stay in the browser window.
Frequently asked questions
- What is the experimenter expectancy effect?
- The experimenter expectancy effect (also called the Rosenthal effect) is the distortion of results by the expectations of the person conducting a study. It can work through how participants are treated or through how ambiguous observations are scored, usually without anyone noticing.
- What did Rosenthal and Fode’s rat experiment show?
- In 1963 students trained rats said to be bred bright or dull; in fact the labels were random. The “bright” rats did better in a T-maze (2.32 versus 1.54 correct choices per day). Whether the animals really learned better or were only scored better cannot be separated in that study.
- What does Clever Hans have to do with the experimenter effect?
- Around 1904 the horse Clever Hans appeared to do arithmetic in Berlin. In 1907 Oskar Pfungst showed that it responded to tiny, unconscious movements of the questioners and stopped tapping when they relaxed. If nobody in sight knew the answer, Hans failed.
- How does the app “The experimenter in the experiment” work?
- You rate twelve rat runs and learn in the debriefing that they were six identical pairs. Then you compare with the 1963 data, explore a model with a double-blind switch and give Clever Hans an arithmetic task.
Subject: Psychology
More from Psychology
- Asch lines: the majority is wrong on purpose
- The one-dollar lie
- Forgetting and review
- Perception lab
- Bystander effect: everyone waits, no one helps
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