Study design

doi:10.1136/bmj.a3191

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John Fletcher, clinical epidemiologist

¹BMJ, London WC1H 9JR

jfletcher{at}bmj.com

A neurologist wanted to study the risk of stroke and transient ischaemic attack in people with a diagnosis of migraine. From her headache clinic she selected cases of migraine and controls without migraine. She collected stroke and transient ischaemic attack outcomes by writing to all subjects and their general practitioners five years …