What type of study examines a population with a similar attribute, differing in one specific variable at a certain point in time?

The type of study that examines a population with a similar characteristic but differing in one specific variable at a single point in time is a cross-sectional study. This design is ideal for gauging the prevalence of a condition or attribute within a specific population and can provide insights into associations between variables.

In a cross-sectional study, data is collected at one specific time, allowing researchers to analyze the relationship between the differing variable and the similar attribute across the entire sample. For instance, if researchers wanted to explore the presence of a specific disease across different age groups in a population, they would gather data from all participants at the same time, categorizing them based on age while noting the presence or absence of the disease.

In contrast, longitudinal studies track the same group over multiple time points to observe changes over time, cohort studies follow a specific group that shares a common characteristic over time to monitor outcomes, and case-control studies retrospectively compare subjects with a specific condition to those without it, examining prior exposure to risk factors. Thus, the cross-sectional study is uniquely positioned for the aim described in the question.