Consecutive sampling

In the design of experiments, consecutive sampling is a sampling technique in which every subject meeting the criteria of inclusion is selected until the required sample size is achieved. Consecutive sampling technique involves selecting all individuals who agree to participate, provided they meet pre-extablished criteria, until the number of subjects desired has been recruited. For example, the author of this text once conducted a study of the verbal memory of adult dyslexics who were recruited by means of several techniques including appeals through newspaper and radio advertising. In order to qualify as subjects, several criteria had to be satisfied with respect to age, IQ level, educational achievement, history of remediation, mental and physical status, and scores on standardized tests of reading ability, among other factors. Consecutive sampling can be highly useful when the available subject pool is limited or when using selection criteria so stringent as to reduce the number of subjects to a point that threatens the generality of findings. Although consecutive sampling methods are typically stronger than other nonprobability methods in controlling sampling bias, such confounding influence cannot be ruled out. Response rate, the proportion of the subjects willing to participate of those selected, may also influence the validity of inferences. For instance, subjects who agree to participate may have different motivations or life circumstances than those who do not.