Research design issues in grouping-based tests☆
Abstract With grouping, a sample is sorted by an observable variable and the mean values of the dependent variable in the extreme-ranked groups are compared. We show that test power is maximized when the two extreme groups each contain 27% of the sample, a much larger percentage than that typically used in the literature. This result is not sensitive to the distribution of the dependent variable. We also show that regression is unambiguously more powerful than grouping, even when the independent variable is measured with error.
SUMMARY A significant rate of implant failures in clinical practice still persists today. This causes many problems for both, dentist and patient. The aim of this study was to evaluate the available literature, presenting a clinical report and also to discuss subjects relating to implant failures during osseointegration. The literature research pointed out the various factors possibly involved in implant failures and how their occurrence may be minimized.