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.
Panel analysis uses panel data to examine changes in variables over time and differences in variables between subjects. In a rolling cross-section, both the presence of an individual in the sample and the time at which the individual is included in the sample are determined randomly.