In 2007 Pronto Ltd ascertained the amount spent on advertising and the corresponding sales revenue by seven marketing clients (Table 8.14).

(a) Plot a scatter plot and comment on a possible relationship between sales and advertising.

(b) Use Excel regression functions to undertake the following tasks:

(i) Fit linear model 

(ii) Check model reliability (r and COD)

(iii) Undertake appropriate inference tests (t and F test)

(iv) Check model assumptions (residual and normality checks)

(v) Provide a 95% confidence interval for the predictor variable.

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Advertising (£000s), x Table 8.14 2 LO 5 4 6 3 7 8 Sales (£000s), y 60 100 70 90 80 105 115