Question

1. What guidelines are used to determine the number of subjects to see in an experiment?

2. How does a with-in subjects experiment differ from a between-subjects experiment?

Answer 1

Answer 1. number of subjects that are to be taken in a research study is completely dependent on the nature of study, variables to be covered (dichotomous or continuous variable) , availability of subjects, topic to be studied. When the research is based on specifically rare cases or a pilot study on issues with low prevalence rate in population, a small number of subjects are used. Like: study of low self esteem and bullying among young men suffering from heterochromia iridium, But when the topic is general enough and variables are dichotomous a large sample may be taken depending upon population. for example: an exploratory study of self-esteem among adolescents in North America.

Answer 2. A within-subjects experiment, the subjects are tested under all treatment or independent variables, as studied by the researcher. For example, as a treatment of substance abuse a particular group of people may be provide with antabuse medication, behavioral therapy, then cognitive therapy to see the effectiveness of each intervention. Whereas in a between-subjects experiment the various experimental treatments or independent variables are introduced to different group of subjects. For example, the same sample may be separated into three groups: one with antabuse drugs, one with behavioral therapy, one with cognitive therapy each.