Question

ch 9 a researcher studying the effect of price cuts on consumers’ expectations makes up two different histories of the store price of a hypothetical brand of laundry detergent for the past year. eight students in a class view one or the other price history on a computer. some students see a steady price, whereas others see regular sales that temporarily cut the price. students are asked the price they would expect to pay. this is an example of

○ a randomized observational study.

○ a two - factor design.

○ a randomized comparative experiment.

○ a matched pairs experiment.

Explanation:

First Question (about price cuts and consumer expectations)

1. Analyze each option:

• A randomized observational study: Observational studies don't assign treatments, but here students are assigned to see different price histories (a treatment), so this is incorrect.
• A two - factor design: There's only one factor (price history: steady or with sales) here, not two, so this is incorrect.
• A randomized comparative experiment: The researcher randomly assigns students (eight students) to two groups (see steady price or price with sales) to compare the effect on their expected price. This fits the definition of a randomized comparative experiment.
• A matched pairs experiment: Matched pairs involve pairing subjects and assigning different treatments to each pair. Here, there's no pairing, just random assignment to two groups, so this is incorrect.

In the Salk vaccine trial, students were randomly assigned to two groups (vaccine or placebo). This is a randomized comparative experiment (or a randomized controlled trial). The key is the random assignment of subjects to different treatment groups (vaccine or placebo) to compare the outcomes (evidence of polio).

Answer:

C. a randomized comparative experiment

Second Question (Salk vaccine trial, though the question part is incomplete, assuming a common question like identifying the study type)