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Define what a pp value represents in the context of an experiment and state the standard threshold for declaring an experimental result to be statistically significant.

Question: Define what a pp value represents in the context of an experiment and state the standard threshold for declaring an experimental result to be statistically significant.

Sample answer: A pp value is the probability of obtaining a result at least as extreme as the one observed, calculated under a model that assumes the null hypothesis and the test's other assumptions are true. It is not the probability that the result occurred purely by chance, nor the probability that the null hypothesis is true. By a common convention in psychology, the threshold (significance level) is 0.050.05: a result is declared statistically significant when p≤0.05p \leq 0.05, which means that under the model a result at least as extreme would occur no more than 1 time in 20.

Key points:

  • The pp value is calculated assuming the null hypothesis and the test's assumptions are true, and it concerns results at least as extreme as the one observed.
  • It is not the probability that the result is due to chance alone or that the null hypothesis is true.
  • By a common convention, the threshold for declaring significance is 0.050.05 (p≤0.05p \leq 0.05).

Rubric: Award full points if the student defines the pp value as the probability of a result at least as extreme as the one observed when the null hypothesis and the test's assumptions are taken as true (not as the probability that the result occurred by chance or that the null hypothesis is true) and identifies 0.050.05 as the conventional significance threshold.

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Updated 2026-10-18

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Research Methods in Psychology - 4th American Edition @ KPU

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