Online purposive samples have unknown biases and may not strictly be used to make inferences about wider populations, yet such inferences continue to occur. We compared the demographic and drug use characteristics of Australian ecstasy users from a probability (National Drug Strategy Household Survey, n = 726) and purposive sample (online survey…

Two-phase designs in epidemiological studies of autism prevalence introduce methodological complications that can severely limit the precision of resulting estimates. If the assumptions used to derive the prevalence estimate are invalid or if the uncertainty surrounding these assumptions is not properly accounted for in the statistical inference…

School consultants who rely on direct observation typically conduct observational samples (e.g., 1 30-min observation per day) with the hopes that the sample is representative of performance during the remainder of the day, but the representativeness of these samples is unclear. In the current study, we recorded the problem behavior of 3 referred…

Private tuition refers to tutoring offered outside mainstream teaching. The study sought to establish the difference in prevalence for private tuition among parents, teachers and pupils in public primary schools in Machakos County. The study employed descriptive survey design. The target populations were all teachers, parents and pupils of public…

The purpose of the current study is to investigate the effects of frequency of peer victimization experiences on psychological and academic adjustment during early adolescence, with a focus on testing psychological adjustment as a mediator, as well as differences based on gender and type of victimization. The sample in this short-term longitudinal…

In rebuttal to a critique of the authors' examination of prevalence rate variability for special education categories, it is claimed that a consideration of the nature of prevalence rate data, the correct use of inferential statistics, and the coefficient of variation itself, suggest the objections are not justified. (Author/DB)