Which studies have the greatest difficulty with the loss of subjects?

A) Longitudinal
B) Cross-sectional
C) Clinical
D) Case history

Longitudinal

Relates to research or studies that observe the same subjects over a period of time, often years or decades, to track changes and developments.

Cross-sectional

A study design that analyzes data from a population, or a representative subset, at a specific point in time.

Clinical

Relating to the observation and treatment of actual patients rather than theoretical or laboratory studies.