OCR MEI Further Statistics Minor 2022 June — Question 3

Exam BoardOCR MEI
ModuleFurther Statistics Minor (Further Statistics Minor)
Year2022
SessionJune
TopicPoisson Distribution
TypeGoodness-of-fit test for Poisson

3 Jane wonders whether the number of wasps entering a wasp's nest per 5 second interval can be modelled by a Poisson distribution with mean \(\mu\). She counts the number of wasps entering the nest over 60 randomly selected 5 -second intervals. The results are shown in Fig. 3.1. \begin{table}[h]
Number of wasps0123456789\(\geqslant 10\)
Frequency025512101011140
\captionsetup{labelformat=empty} \caption{Fig. 3.1}
\end{table}
  1. Show that a suitable estimate for the value of \(\mu\) is 5.1. Fig. 3.2 shows part of a screenshot for a \(\chi ^ { 2 }\) test to assess the goodness of fit of a Poisson model. The sample mean has been used as an estimate for the population mean. Some of the values in the spreadsheet have been deliberately omitted. \begin{table}[h]
    ABCDE
    \includegraphics[max width=\textwidth, alt={}]{e8624e9b-5143-49d2-9683-cc3a1082694e-4_132_40_1069_273}Number of waspsObserved frequencyPoisson probabilityExpected frequencyChi-squared contribution
    2\(\leqslant 2\)70.11656.98870.0000
    3358.08741.1786
    44120.2765
    55100.0255
    66100.14908.94000.1257
    77110.10866.51343.0904
    8\(\geqslant 8\)50.14408.6414
    9
    \captionsetup{labelformat=empty} \caption{Fig. 3.2}
    \end{table}
  2. Determine the missing values in each of the following cells, giving your answers correct to 4 decimal places.
    • C3
    • D5
    • E8
    • Explain why some of the frequencies have been combined into the categories \(\leqslant 2\) and \(\geqslant 8\).
    • In this question you must show detailed reasoning.
    Carry out the hypothesis test at the 5\% significance level.
  3. Jane also carries out a \(\chi ^ { 2 }\) test for the number of wasps leaving another nest. As part of her calculations, she finds that the probability of no wasps leaving the nest in a 5 -second period is 0.0053 . She finds that a Poisson distribution is also an appropriate model in this case. Find a suitable estimate for the value of the mean number of wasps leaving the nest per 5-second period.