Table 1 Summary of data collection methods in each country

Austria

up to 6000

646

454

Up to 10 consecutive patients aged 18–65 y visiting any of 400 general practitioners (GPs) and 200 neurologists for any reason on a pre-specified day. Questionnaires to be completed and returned later. One reminder after one month to non-responders.

France

2400

876

586

Consecutive patients aged 18–65 y attending any of a cooperative of 80 GPs on a pre-specified day. Questionnaires to be completed and returned immediately or later by post. One reminder by email after one week to non-responders.

Germany

3000

338

248

Random urban (50 %) and rural (50 %) samples aged 18–65 y from general population listings supplied by local municipal authority. Questionnaires distributed and returned by post. No reminders sent.

Italy

3500

500

374

Random urban (70 %) and rural (30 %) samples drawn from general population using listings supplied by Azienda Sanitaria Locale of Pavia, stratified with regard to gender, age (in range 18–65 y) and education. Questionnaires distributed and returned by post. No reminders sent.

Lithuania

1137

616

440

Sample drawn from Kaunas city and Kaunas region using Residents’ Register Service, reflecting age (in range 18–65 y) and gender composition of Lithuania and proportions living in rural (33 %) or urban (67 %) areas. Data collection face-to-face, conducted by medical students “cold-calling” door-to-door.

Luxembourg

6498

2023

1473

Sample aged 18–65 y, stratified for age, gender, region and nationality, drawn from general population via national social security registry (IGSS). Questionnaires distributed and returned by post. Reminders sent one month later to non-responders.

Netherlands

unknown

2414

1993

Survey conducted by market research company with access to population sample of 200,000, representative with regard to gender, age (in range 18–65 y), region and education. Questionnaire distributed by internet, to be completed on-line. Study stopped when >2000 received back.

Spain

1700

999

797

Random sample of employees of companies operating in national postal services in 10 areas of Spain, stratified to be representative of general working population with regard to gender, age (in range 18–65 y) and education. Ten occupational health physicians delivered and took return of questionnaires. One telephone reminder to non-responders.

United Kingdom

720

128

90

Modified population-based sampling through 12 GP practices in 11 areas (in UK, virtually all residents are registered with local GP). Questionnaire given to consecutive patients aged 18–65 y attending for any reason over a period of time, to be completed and returned immediately, or later by post.