A study was conducted to explore the eects of ethanol onsleep time. Fifteen rats

Question

A study was conducted to explore the eects of ethanol onsleep time. Fifteen rats were randomized to one of three treatments. Treatment 1 got only water (control).Treatment 2 got 1g of ethanol per kg of body weight, and treatment 3 got 2g/kg of ethanol. The amount ofREM sleep in a 24hr period was recorded, in minutes. Data are below:

Treatment 1: 63, 54, 69, 50, 72

Treatment 2: 45, 60, 40, 56

Treatment 3: 31, 40, 45, 25, 23, 28

(a)

According to Fisher's least signicant dierence (LSD) method, is testing for dierences in all pairs of

treatments warranted for these data? Explain fully.

(b)

Regardless of your answer to part (a), calculate 90% confidence intervals for all pairwise comparisons

using Fisher's LSD method. Interpret your results in context.

(c)

For all pairwise comparisons, calculate 90% confidence intervals using the Bonferroni correction. Inter-

pret your results in context. Do any of the results dier from part (b)?

Explanation / Answer

Answers are given as-

(a). The LSD calculates the smallest significant value between two means. This enables you to make direct comparisons between two means from two individual groups. Any difference larger than the LSD is considered a significant result. So in order to check for the similarity or dissimilarity between the three groups we need to use Fisher's LSD in order to get a quantitative term to define. Hence the answer to the question is- yes it is warranted for testing of differences in all pairs of treatments for this data as LSD uses the mean of values for confidence interval calculation rather than the particular group values.

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