Table 1 Electronic bibliographic databases searched and search strategy used

Medline (1996–2004)

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)

CENTRAL (1980–2004)

Cochrane database of systematic reviews (1980–2004)

PsycINFO (1990–2004)

National Research Register (2000–2004)