The study of first choice for the assessment of an unknown or new disease when there is no etiological hypothesis is ___:
Descriptive studies:
→ Descriptive studies are used to describe a disease of unknown etiology.
Steps of descriptive studies :

Defining the population to be studied.
Defining the disease under study.
Describing the disease by

a. Time
b. Place
c. Person

Measurement of disease.
Comparing with known indices.
Formulation of an aetiological hypothesis
Cohort study.
Randomized clinical trials.
Ecological studies.
Descriptive studies.