A 3-year study was carried out to see if fluoride toothpaste helps to prevent cavities. The table gives summary data. The sample mean is the number of new decayed, missing, and filled surfaces. Is fluoride beneficial? Compute the test statistic for a hypothesis test using a significance level of 0.05.
Group Sample Size Sample Mean Sample SD
Without Fluoride 289 12.83 8.31
With Fluoride 260 9.78 7.51