Putting It Together: Naughty or Nice? Yale University graduate student J. Kiley Hamlin conducted an experiment in which 16 ten-month-old babies were asked to watch a climber character attempt to ascend a hill. On two occasions, the baby witnesses the character fail to make the climb. On the third attempt, the baby witnesses either a helper toy push the character up the hill or a hinderer toy prevent the character from making the ascent. The helper and hinderer toys were shown to each baby in a random fashion for a fixed amount of time. The baby was then placed in front of each toy and allowed to choose which toy he or she wished to play with. In 14 of the 16 cases, the baby chose the helper toy.
Why is it important to randomly expose the baby to the helper or hinderer toy first?
c. In testing 12 six-month-old babies, all 12 preferred the helper toy. The P-value was reported as 0.0002. Interpret this result.

Verified step by step guidance

1. Understand the purpose of random exposure: Randomly exposing each baby to either the helper or hinderer toy first helps to eliminate any bias that might arise from the order in which the toys are presented. This ensures that the babies' choices are not influenced by a preference for the first toy they see, but rather reflect their true preference between the helper and hinderer toys.
2. Recognize the role of randomization in experiments: Randomization helps to balance out other confounding variables that could affect the babies' choices, such as fatigue, attention span, or novelty effects, making the results more reliable and valid.
3. Interpret the P-value of 0.0002: The P-value represents the probability of observing the data, or something more extreme, assuming the null hypothesis is true. Here, the null hypothesis might be that babies have no preference between the helper and hinderer toys (i.e., a 50/50 choice).
4. Since the P-value is very small (0.0002), it indicates that the observed result (all 12 babies preferring the helper toy) is highly unlikely to have occurred by random chance if there were truly no preference. This provides strong evidence against the null hypothesis.
5. Therefore, the result suggests that six-month-old babies have a statistically significant preference for the helper toy, supporting the idea that they can distinguish and prefer prosocial behavior even at a young age.

Key Concepts

Randomization

Randomization is the process of assigning subjects or treatments in a study by chance to reduce bias. It ensures that each participant has an equal chance of experiencing different conditions, which helps isolate the effect of the treatment from other variables. In this experiment, randomizing the order of exposure to the helper or hinderer toy prevents order effects from influencing the babies' choices.

P-value and Statistical Significance

The P-value measures the probability of observing results as extreme as those in the study, assuming the null hypothesis is true. A small P-value (typically less than 0.05) indicates strong evidence against the null hypothesis, suggesting the observed effect is unlikely due to chance. Here, a P-value of 0.0002 means there is a very low probability that all 12 babies preferring the helper toy happened by random chance.

Experimental Design and Control

Experimental design involves planning how to conduct a study to test hypotheses effectively, including controlling variables that might affect outcomes. Controls, such as consistent exposure time and conditions, help ensure that differences in results are due to the treatment itself. In this study, controlling the exposure time and randomizing toy presentation helps attribute babies’ preferences specifically to the helper or hinderer roles.