Question

in countries known to contain lower levels of vitamin d, there were more reported cases of a particular type of rare disease. some researchers hypothesized that a deficiency in vitamin d would increase the risk of developing the disease. these researchers compared vitamin d levels in blood samples from 110 military personnel who have developed the disease with blood samples of nearly 310 who have not. the samples were taken, on average, five years before the disease was diagnosed. those with the highest blood vitamin d levels had a 61% lower rate of developing the disease than those with the lowest levels. complete parts a) through d).
a) what kind of study was this? select all that apply.

• prospective
• observational
• experiment
• retrospective

Explanation:

1. Prospective: A prospective study follows a group forward in time. Here, samples were taken before disease diagnosis and then followed to see disease development, so it's prospective.
2. Observational: Researchers observed and compared existing groups (those with/without disease) without manipulating variables, so it's observational.
3. Retrospective: A retrospective study looks back at past data (here, blood samples taken before diagnosis, analyzing them after disease developed) to find associations, so it's retrospective.
4. Experiment: An experiment involves manipulating a variable (e.g., assigning vitamin D levels), but here researchers just observed existing data, so not an experiment.

Answer:

Prospective, Observational, Retrospective