Question

ch 9 in the salk vaccine trial of 1954, almost 400,000 students (grades 1–3) in 11 states participated. students were randomly assigned to either a vaccine or placebo injection. all students were observed for evidence of polio during the school year.
which of the following might be a lurking variable in the salk vaccine experiment?

☑️ general health of the students

☑️ socio - economic status

☑️ area of residence

question 15
1 pts
ch 9 a placebo is an important element of many clinical trials because

☑️ use of the placebo can help avoid confounding.

☑️ it serves as a control for the experiment.

□ it allows the researcher to adjust for psychological effects of receiving medical attention.

Explanation:

First Question (Lurking Variable in Salk Vaccine Experiment)

A lurking variable is a variable not included as an explanatory or response variable in the analysis but that can affect the relationship between them. In the Salk vaccine trial, general health of students (healthier students may have different polio incidence), socio - economic status (access to healthcare, hygiene), and area of residence (polio prevalence in different regions) can all impact polio occurrence and are not directly part of the vaccine - placebo assignment, so they are lurking variables.

• A placebo helps avoid confounding by keeping other factors (like patient expectations) constant between treatment and control groups.
• It serves as a control, providing a baseline to compare the treatment (vaccine) against, so we can see the true effect of the vaccine. The option about adjusting for psychological effects of medical attention is incorrect as placebos mainly act as a control/confounding - avoidance tool, not for adjusting psychological effects in that way.

Answer:

general health of the students, socio - economic status, area of residence

Question 15 (Importance of Placebo in Clinical Trials)