Final answer:
Cross-sectional studies measure prevalence, which is the total number of both new and existing cases of a disease or condition in a population at a single point in time. They do not measure incidence, risk ratio, or odds ratio, which are associated with longitudinal studies such as cohort studies.
Step-by-step explanation:
Cross-sectional studies are designed to measure the current state or prevalence of a disease or condition in a particular population at a single point in time. Unlike cohort studies, which can measure incidence over a period, or calculate risks like the risk ratio and odds ratio, cross-sectional studies focus on the existing cases, both new and chronic, to provide a snapshot of the health status of a population. The correct answer to the question is b) Prevalence. Incidence refers to the count of new cases of a disease that develop in a specific time period, which helps understand risk factors and disease spread. In contrast, prevalence accounts for both new and existing cases at a point in time, offering insight into the overall disease burden within a community. The prevalence can serve as an indicator of the healthcare burden and is often represented as a prevalence rate, calculated as Incidence multiplied by disease duration. The formula presented, Prevalence rate = Incidence x duration, illustrates how these measures are related, but prevalence is the measure captured in cross-sectional studies since they look at the total number of cases present at a certain time without considering the length of time the disease has been present.