Table 1.

Electronic bibliographic databases searched and search strategy used

Database	Host	Search Strategy
Medline (1996–2004)	Ovid	1. Health care survey* or Questionn* 2. Respons* or Respons* adj rate or follow adj up or return 3. Post* or mail* 4. Enhanc* or improv* or promot* or increas* or influenc* or maximis* 5. Remind* or letter* or postcard* or incentiv* or reward or money or payment or lottery or prize or personalis* or sponsor or length or style or format or appearance or colour or color or stationary or envelope or stamp or postage or certified or registered or telephone or notice or dispatch or deliver or sensitive or disseminate 6. Randomi* or control* or trial* 7. 1 and 2 and 3 and 4 and 5 and 6
Embase (1980–2004)	Ovid
CENTRAL (1980–2004)	Update Software ltd
Cochrane database of systematic reviews (1980–2004)	Update Software ltd
PsycINFO (1990–2004)	Ovid
National Research Register (2000–2004)	DoH (Web version)