Often called quartz topaz, citrine topaz, or topaz, all of which are misleading. It is yellow, amber, to amber brown. While a pleasing stone in terms of colour, and fairly durable, citrine is slightly softer and has less brilliance than precious topaz.
In this respect, a cohort study is often interchangeable with the term naturalistic observation. There are two main sub-types of cohort study, the retrospective and the prospective cohort study. The major difference between the two is that the retrospective looks at phenomena that have already happened, whilst the prospective type starts from the present. . The retrospective case study is historical in nature.
cohort. Clinical trials A group of persons with a common characteristic, set of characteristics or exposure, who are followed for the incidence of new diseases or events, as in a cohort for a prospective study.n epidemiology a group of individuals who share a characteristic acquired at the same time. The term usually refers to a birth cohort, which contains animals born in a specified time period. cohort studies. a prospective or follow-up, analytical, epidemiological study.