12. A 3-year study was carried out to see if uoride toothpaste helps to prevent cavities ( Clinical Testing of Fluoride and non-Fluoride Containing Dentifrices in Hounslow School Children, British Dental J., Feb., 1971: 154—158). The dependent variable was the DMFS increment, the number of new Decayed, Missing, and Filled Surfaces. The table gives summary data.

Sample Sample Sample Group Size Mean SD Control 289 12.83 8.31 Fluoride 260 9.78 7.51 Calculate and interpret a 99% con dence interval for the difference between true means. Is uoride toothpaste bene cial?