The data in Table 1.6.2 were extracted from a study conducted at the Dental School of the University of Sao Paulo. They correspond to the measurements of a dental plaque index ˜ (on a scale that...

The data in Table 1.6.2 were extracted from a study conducted at the Dental School of the University of Sao Paulo. They correspond to the measurements of a dental plaque index ˜ (on a scale that ranges from zero to four) obtained for each of fourteen male and twelve female preschoolers, before and after the use of a conventional or an experimental toothbrush. One of the objectives of the study was to compare the two toothbrushes with respect to the reduction of dental plaque controlling for the motor ability of the female and male children

and to estimate the corresponding average reduction in dental plaque after tooth brushing. Specify different statistical models for the the problem stating the assumptions and indicating whether the corresponding inferential methods are exact or approximate. [Suggestions may be obtained in Singer and Andrade (1997).]