Adata safety monitoring board report for an investigator-initiated investigational drug study indicates a significantly higher than anticipated rate of an expected adverse event. this event required revision of the informed consent form to disclose the higher rate. a change in the eligibility criteria of the protocol to reduce the risk was implemented. current subjects would be reconsented.

Donald is studying the eating habits of all students attending his school. he samples the population by dividing the students into groups by grade level and randomly selecting a proportionate number of students from each group. he then collects data from the sample. which type of sampling is used? select the correct answer below: systematic sampling convenience sampling stratified sampling cluster sampling