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.
1 It is a retrospective study. 2  This means that (like a detective) you begin at the end, with the disease, and then work backwards, to hunt for possible causes. 3  In our example, you could identify a group of patients with brain cancer (these would be the cases in case-control).here a cohort study is designed to identify causal factors for a disease, you would begin by selecting a sample of people who do not have the disease (so, prevalence = zero). You would then follow them over time. Some incident cases would arise, and these would provide you with an estimate of prevalence.