If the two pandas have a cub, the new contract states the Memphis Zoo does not have to pay China a yearly fee on that. However, the cub will have to be returned to China after four years.
Panel study. A panel study is a longitudinal study design where a cross-sectional sample of units is selected and surveyed at usually regular intervals. The observation units may be individuals, households, firms or other organisations, or even countries. Household panel surveys are an important sub-type of panel study.
A cohort study is a panel study, but a panel study is not always a cohort study as individuals in a panel study do not always share a common characteristic. A cohort study is a quasi-experiment used in medicine, nursing, psychology, social science, actuarial science, business analytics, and ecology.