The political scientist from Exercise 11 also claims that for Parliaments of 4, 4.5, and 5 years in length, the mean number of times the Senate has sat during a session is equal. The table shows, in three samples grouped by length in years, the number of times that the Senate has sat in each Parliament.
a. At the 0.05 level of significance, test the claim that all three groups have the same mean number of Senate sittings.
b. Based on Tukey's method of simultaneous confidence intervals, between which groups, if any, is there a significant difference?

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Length of Parliament in Years 201 158 383 217 257 261 478 339 352 241 283 366 357 255 363 Based on data from Duration of Sessions of Parliament, Library of Parliament