Lesson 3 · Observational Designs · Step 1 of 6
What descriptive designs can and cannot tell us
In June 1981, a short CDC report described five previously healthy young men in Los Angeles with a pneumonia seen only in severely immunocompromised patients. Case reports like that one, and the Brazilian case series that linked Zika to microcephaly, are how new problems get noticed. They generate hypotheses. With no denominator they can't say how common something is, and with no comparison group they can't show cause. Surveillance watches a whole population continuously, with standard case definitions, so it can trigger a response. It shares the limit: it describes what is happening, not why.
Also covered: case reports and case series · public health surveillance · hypothesis generation · denominators
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Lesson 3 · 6 steps
Research Designs · lesson 3 of 5