A dentist wishes to determine the quality of dental hygiene of patients attending a particular dental practice. He decides to record the standard of hygiene of the first five patients he sees each day for one week. Is this procedure likely to give him a representative sample? Why?
In a study looking at the effect of fluoridation on caries prevalence in children in Wick, Scotland the researchers studied two groups of children one whilst the local water was fluoridated and one five years after it was defluoridated. In both cases the examined all 5-6 year old children in the town. They found an 10% reduction in the number of caries-free children.
From the point of view of sample selection, would we be correct in assuming that this study proves that defluoridation of the water supply causes an increase in caries in children? Why?
A study was carried out to investigate the expectations of oral-implant-retained prostheses in a UK dental hospital. The study included two groups: "(1) a group of edentulous adults who requested implant therapy('implant group'); and (2) an edentulous control group, of similar age and gender distribution as the implant group, receiving conventional dentures." The study found some evidence that the implant group had expectations of there dentures that were over-optimistic
What is the fundamental problem in the selection of patients in this study?