Answer:
Cross-sectional research gathers data to compare across groups. It is conducted and analyzed at the same time. If people undergo intellectual decline as they age, people who are older in the study will have different results in the intelligence testing category compared to younger people. Longitudinal studies gather data on the same subjects more than once, over a span of time. If participants undergo intellectual decline as they age during a longitudinal study, that will impact the study, and be recorded.
Fluid intelligence is the ability to problem solve and reason in novel or unique situations, and crystallized intelligence is the ability to use previously acquired knowledge or personal experience to problem solve or reason. These two phenomena could change over time through intellectual decline. If someone goes through intellectual decline, it will be harder for them to reason, problem solve, or pull knowledge from past experiences, thus influencing how fluid and crystallized intelligence works from individual to individual.
Explanation:
