CAIE S2 2024 June — Question 7

Exam BoardCAIE
ModuleS2 (Statistics 2)
Year2024
SessionJune
TopicHypothesis test of binomial distributions
TypePerform one-tailed hypothesis test

7 Every July, as part of a research project, Rita collects data about sightings of a particular kind of bird. Each day in July she notes whether she sees this kind of bird or not, and she records the number \(X\) of days on which she sees it. She models the distribution of \(X\) by \(\mathrm { B } ( 31 , p )\), where \(p\) is the probability of seeing this kind of bird on a randomly chosen day in July. Data from previous years suggests that \(p = 0.3\), but in 2022 Rita suspected that the value of \(p\) had been reduced. She decided to carry out a hypothesis test. In July 2022, she saw this kind of bird on 4 days.
  1. Use the binomial distribution to test at the \(5 \%\) significance level whether Rita's suspicion is justified.
    In July 2023, she noted the value of \(X\) and carried out another test at the \(5 \%\) significance level using the same hypotheses.
  2. Calculate the probability of a Type I error.
    Rita models the number of sightings, \(Y\), per year of a different, very rare, kind of bird by the distribution \(B ( 365,0.01 )\).
    1. Use a suitable approximating distribution to find \(\mathrm { P } ( Y = 4 )\).
    2. Justify your approximating distribution in this context.
      If you use the following lined page to complete the answer(s) to any question(s), the question number(s) must be clearly shown.