The table below gives data for the percentage area of a person's teeth coated with plaque (a colourless bacterial biofilm that forms on hard surfaces in the mouth) after using one of four different toothpastes for four successive fortnights.
(a) What analysis would you use for this design?
(b) Use a statistical package to analyse the data. Is there a significant difference among toothpastes?
(c) Use an a posteriori test to identify the most effective toothpaste(s). Which would you recommend?
(d) Are there any you would not recommend?
