As individuals, groups, communities and the total population and their characteristics are interrelated and intermingled and any study conducted on them is flexible and not typical.

Ecological study can be a group based analytical study in addition to be of descriptive nature.

Cross-sectional study can be both descriptive as well as analytical one, descriptive when one variable or each variable in a group or population is studied, analytical as it provides information about the presence and strength of association. (Oxford textbook of public health)