# In a study of methods of producing sheep's milk for use in cheese manufacture, ewes were randomly allocated to either a mechanical or a manual milking method. The investigator suspected that the mechanical method might irritate the udder and thus produce a higher concentration of somatic cells in the milk. The accompanying data show the average somatic cell count for

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In a study of methods of producing sheep's milk for use in cheese manufacture, ewes were randomly allocated to either a mechanical or a manual milking method. The investigator suspected that the mechanical method might irritate the udder and thus produce a higher concentration of somatic cells in the milk. The accompanying data show the average somatic cell count for each animal.

(a) Do the data support the investigator's suspicion? Use a t test against a directional alternative at Î± = 0.05. The standard error of (1 - 2) is SE = 427.54 and formula (6.7.1) yields 9.2 df.
(b) Do the data support the investigator's suspicion? Use a Wilcoxon-Mann-Whitney test against a directional alternative at Î± = 0.05. (The value of the Wilcoxon-Mann-Whitney statistic is Us = 69.) Compare with the result of part (a).
(c) What condition is required for the validity of the t test but not for the Wilcoxon-Mann-Whitney test? What features of the data cast doubt on this condition?
(d) Verify the value of Us given in part (b).

Related Book For

## Statistics For The Life Sciences

5th Edition

Authors: Myra Samuels, Jeffrey Witmer, Andrew Schaffner

ISBN: 9780321989581