Evolutionary theory builds on the work of Darwin

Ricardo wants to study the academic performance of graduate students in the United States. First, he decides that he will study schools in only 15 states and randomly selects those states. He then randomly selects 30 schools from these 15 states. Over a period of 3 months, Ricardo travels to these 30 schools and studies the academic performance of their students. Identify the sampling technique used by Ricardo in this scenario.

What will be an ideal response?

For an important characteristic, you would expect the highest correlations between

(a) fraternal twins reared together (b) fraternal twins reared apart (c) identical twins reared together (d) identical twins reared apart (e) not enough information is given to answer the question