Table 1 Question wording.

Variable	Internet sample		Natsal sample
Age	How old are you?		In which month and year were you born?
Employment status	Which of the following best applies to you or your work in the last week?		Which of these descriptions applies to what you were doing last week?
Ethnic group	Which of the following ethnic groups best describes you?		To which of the ethnic groups on this card do you consider you belong?
Higher education	Could you tell us what your highest educational qualification is?		Have you passed any exams or got any of the qualifications on this card?
Social class	Coded on the basis of a similar series of questions in both surveys, according to the National Statistics Socio‐Economic Classification. Students were not asked these questions in the web survey and are therefore excluded from social class coding in both surveys.
Residence	Where do you currently live?		Coded on the basis of postcode sector.
Urban area	Which best describes the area you live in?		Coded by the interviewer.
Country of birth	Were you born in the UK? What country were you born in?		Were you born in England, Wales, Scotland, Northern Ireland/Eire or another country?
Self‐reported health	In general, how would you rate your health in the past 3 months?		How is your health in general?
Alcohol consumption	In the past 12 months, please indicate how often (on average) you have used alcohol.		How often have you had an alcoholic drink drink of any kind during the last 12 months?
Drug injecting	Have you injected drugs (other than anabolic steroids) in the past 12 months?		When was the last time you injected yourself with non‐prescribed drugs or other substances?
First sex with male	How old were you the first time you had sex of any kind with another male?		Have you ever had ANY kind of sexual experience or sexual contact with a male? How old were you the first time that happened?
Ever had an HIV test	Have you ever had an HIV test?		Apart from any occasion when you were donating blood, have you ever had a blood test that involved testing for HIV?
Had STI	Have you had a sexually transmitted disease (STD) in the last year?		Have you ever been told by a doctor that you had any of the following? When were you told by a doctor that you had ‘x'?
AI	In the past 3 months have you had anal sex with a condom? In the past 3 months have you had anal sex without a condom?		When, if ever, was the last occasion you had anal sex with a man?
UAI	In the past 3 months have you had anal sex without a condom?		In the last year, when you've had anal sex, how often have you, or your partner, used a condom?

AI, anal intercourse; STI, sexually transmitted infection; UAI, unprotected anal intercourse.

The questions listed are necessarily abridged because of space restrictions. A copy of the online survey may be obtained from ARE. A copy of the Natsal 2000 questionnaire may be obtained from the UK Economic and Social Research Council Question Bank at http://qb.soc.surrey.ac.uk/surveys/nssal/nssal00.htm.