In each of the following situations, identify the sample as an SRS, a stratified random sample, a multistage random sample, or a voluntary response sample. Explain your answers.

a.There are seven sections of an introductory statistics course. A random sample of three sections is chosen, and then random samples of eight students from each of these sections are chosen.

b.A student organization has 55 members. A table of random numbers is used to select a sample of five.

c.An online poll asks people who visit this site to choose their favorite television show.

d.Separate random samples of male and female first-year college students in an introductory psychology course are selected to receive a one-week alternative instructional method.

a) The seven sections of an introductory statistics course formed the strata since the are all from the sample population but with different features - sections which is assumed to be, perhaps a different topics. Hence, three of the sections are selected randomly and eight students were sampled from each selected stratum. This population are homogeneous within each stratum. That is, they have similar features. Therefore, it is Stratified random sample.

b) This is a direct numbering of people in which we try to ensure unbiased selection of individual. Hence, the use of random numbers to pick the needed five students into the sample. That is, we can just give each student in the organisation, a number from 1 to 55. And each students know his/her number. Then, we use the random number to do a raffle draw of these numbers to select any number associated with the student. Therefore, it is SRS.

c) For an online poll, it is voluntary to participate and we don't even who those that might visit the website before hand. And we cannot make anyone participate unless he/she chose to do so. However, we hopeful that some individuals will be persuaded by the request to participate. Therefore, it is a voluntary response sample.

d) This is a multistage random sample. We can assume that they have first been selected from the class regardless of the gender randomly in the first selection. Then, we go a step further to classify them by gender and conduct another rounds of selection from the two groups using gender.