Exposure definition
All three studies had national prescription registries as source of their exposure data. Study 1 considered women as exposed to HC if having a valid prescription within the last six months prior to either use of antidepressants or getting a depression diagnosis. Study 22 considered a valid prescription of HC as being exposed. Study 33 considered a valid prescription of HC within the first four weeks after prescription as non-use, so that women were considered users of HC from four weeks after starting use of HC. The argument was that women could not develop a depression or start use of antidepressants due to use of HC so quickly after starting this use.
Study 1 and 2 followed women from they started using HC, whereas study 3 examined current users (Table 2).