The cognitive research carried out to develop the questions on duration of cohabitation resulted in the following approach. Respondents were asked how long each completed cohabitation had lasted and then asked to give either the start date or the end date. The other date was then calculated in the interview and checked with the respondent, who could disagree and correct it. Length of cohabitation was based on the corrected dates where required.

First previous cohabitations which did not end in marriage tended to be longer than the second such cohabitations.

• Among people aged 16 to 59, around 44% of first cohabitations lasted for less than 2 years compared with 56% of second cohabitations. The difference was more marked among men.

First cohabitations which were the only past cohabitation tended to be longer than those which were the first of two or more. Again the differences were more marked among men.

• The mean length of a first and only completed cohabitation was 35 months for men and 42 months for women compared with the median length of 25 months for men and 30 months for women for a cohabitation which was the first of two or more