Question

These data describe spending by a major pharmaceutical company for promoting a cholesterol-lowering drug. The data cover 39 consecutive weeks and isolate the area around Boston. The variables in this collection are shares. Marketing research often describes the level of promotion in terms of voice. In place of the level of spending, voice is the share of advertising devoted to a specific product.
The column Market Share is sales of this product divided by total sales for such drugs in the Boston area. The column Detail Voice is the ratio of detailing for this drug to the amount of detailing for all cholesterol-lowering drugs in Boston. Detailing counts the number of promotional visits made by representatives of a pharmaceutical company to doctors’ offices. Formulate the SRM with Y given by the Market Share and X given by the Detail Voice.
(a) Identify the week associated with the outlying value highlighted in the figure below. (The figure shows the least squares fitted line.) Does this week have unusually large sales given the level of promotion, or unusually low levels of promotion? Take a look at the timeplots to help you decide.
(b) How does the fitted regression equation change if this week is excluded from the analysis? Are these large changes?
(c) The r2 of the fit gets larger and se gets smaller without this week; however, the standard error for b1 increases. Why?
(d) These are time series data. Do other diagnostics suggest a violation of the assumptions of the SRM?


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  • CreatedJuly 14, 2015
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