Question

A researcher wanted to determine the number of antibodies a person has in their blood after getting a vaccine for a certain virus. To determine this, the researcher randomly selected 1,500 people who had received the vaccine, drew a blood sample, and determined the number of antibodies for each person.

Answer 1

This is an example of a cross-sectional study,

Explanation:

As the researcher is measuring the number of antibodies at a single point in time for a randomly selected group of people who have already received the vaccine. It is also an example of observational research, as the researcher is not intervening in any way and is only observing and measuring the antibodies in the blood samples.