Question

1. what do epidemiologists study?

risk factors for different diseases
blood and heart diseases
how often a disease occurs in a particular area or group of people
non - infectious diseases and their causes

Explanation:

Epidemiologists study the distribution and determinants of health - related states or events in specified populations. This includes looking at how often a disease occurs in a particular area or group of people (incidence and prevalence). While they may consider risk factors (but this is more of a part of the broader study of disease distribution), they don't just focus on blood and heart diseases or non - infectious diseases only.

Answer:

how often a disease occurs in a particular area or group of people