2 MCS3 DATA
2.1 The following definitions are used throughout this section:
- Productive: The families with some data from at least one of the data collection instruments other than data carried forward from previous sweeps.
- Ineligible: Emigrations and child deaths.
- Uncertain eligibility: Families who were away temporarily and those whose eligibility was uncertain, including untraced movers.
- Unproductive: Refusals (whether or not 'permanent'), non-contacts, other non-responses including language problems, ill/incapacitated, deleted/lost data (files lost in fieldwork).
2.2 The Sweep 3 sample of the Millennium Cohort Study ( MCS3) includes all those who were productive cases at the MCS3 face-to-face survey including those who were productive at MCS1 but missing at MCS2, and new families interviewed at sweep 2, who were re-interviewed at MCS3 ( Table 2.2).
2.3 At each following sweep child deaths and emigrations are excluded from the eligible population. After further exclusions of families who were judged to have refused permanently and some cases of sensitive family circumstances, the UK-wide sample issued for fieldwork at MCS sweep 3 was 18,528 families (see Ketende, 2008, and Hansen, 2008, for more details).
MCS3 response rate
2.4 There were 15,246 productive families in the UK sample at sweep 3 including 1,814 families in Scotland. This was 344 fewer UK families than at sweep 2. This relatively small difference was because of a productive response at MCS3 from 1,444 families who had been unproductive at sweep 2. This has kept the sweep 3 sample size at virtually the same level as sweep 2.
2.5 Table 2.1 shows those who were productive at MCS3. The productive sample has remained virtually the same between sweeps 2 and 3, which is a remarkable achievement for the fieldwork team, the CLS tracing team and the cohort families themselves.
2.6 There are no statistically significant differences by UK country in productive responses.
MCS longitudinal sample
2.7 The MCS longitudinal participation is presented in Table 2.23, which shows that 1596 families in Scotland participated at all 3 sweeps of the MCS, and a further 218 families participated at sweep 3 although not at sweep 2. Across the UK as a whole 13,802 families (13,234 from sweep 1 and 568 who joined MCS at sweep 2) have participated in all sweeps that they were eligible for.
2.8 In most of the rest of this report the UK countries are broken down by the families' location at the sweep 3 interview. This was not necessarily the same as for previous surveys, as some families had moved. Table 2.3 shows that the number of movers was small, comparing country at the age 5 interview with that in which the family was sampled for sweep 1. A total of 1768 out of 1804 cases were still living in Scotland and 15,031 of the 15,241 UK cases were still in their original country. A small number of families moved from one UK country to another between sweeps 1 and 3; 46 cases had moved out of Scotland and 36 cases had moved to Scotland by sweep 3 (a net loss of 10 families). The largest flows were in and out of England, which had the largest net gain of families productive at sweep 3 (n=43). Wales had the largest net loss of 34 families, mostly moving to England.
Analyses in this report
2.9 All analyses contained in this report were weighted using the appropriate sample and country weights. Further details on the sample weights available and weights used can be found in Hansen and Joshi (2008, pages 13-14). In addition, where cell sizes were under 30 cases, statistics are placed in parentheses to draw attention to the small cell sizes.
2.10 Some of the tables presented are of the separate cross-sectional waves of MCS data. It should be noted that comparisons across cross-sectional cohorts are not necessarily based on identical respondents. In other cases, longitudinal analyses are carried out where respondents are the same parents/children across more than one wave of data.