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Table 1 Distribution of pupil level variables (all pupil level analyses involved 5,092 cases, except for the early school leavers' sub-group analysis as described in the text).

From: What explains between-school differences in rates of smoking?

  Descriptive Statistics as appropriate to scale of measurement Missing data N (%) How missing data was handled Possible reason for the missing data
Gender 47% male 0 (0) N/A N/A
Age in months at time of first interview Mean = 169.8, sd = 3.9 471 (9.2) Mean substitution by school and by gender Some pupils were wary of providing their data of birth (necessary to calculate the age at time of interview) as they believed the answer could potentially be used to track their identity, thus they opted to leave it blank. Naturally, we had explained that we were not interested their identities.
Cohort (there were two cohorts) 52% belonged to cohort 1 0 (0) N/A N/A
Early school leavers 88% of pupils stayed on at school beyond the minimum legal age for attending school (16 years) 0 (0) N/A N/A
Family structure 75% lived with both parents, 21% with Mum only, 3% with Father only and 1% with neither parent. 0 (0) N/A N/A
Housing type 69% of pupils lived in privately owned housing, 22% rented housing and 0.2% were in care or foster homes 469 (9.2) A separate category was coded for missing data Some pupils were unsure if they lived in privately owned housing or not.
Parental monitoring (high vs low) 60% of pupils experienced high parental monitoring 0 (0) N/A N/A
Father occupational class (manual vs non-manual) 35% worked in manual occupations 1199 (23.5) A separate category was coded for missing data Some pupils found the questions about parental occupation intrusive and so left them blank. Others provided textual information that we did not find possible to classify.
Spending money (high vs low) 51% had over £15 spending money (high) 20 (0.4) N/A A few pupils did not get a consistent amount of spending money and felt they could not complete this question.
Ethnicity 96% of the pupils were 'white' 51 (1.0) A separate category was coded for missing data Some pupils did not see the point in the question and objected by leaving it blank
Mothers' age (<40 vs older mother) 49% had a mother over 40 years 720 (14.1) A separate category was coded for missing data Some pupils did not know their Mum's age and some did not see the point of the question and objected by leaving it blank (despite us explaining why we asked, whenever the issue was drawn to our attention).
Religious belief (5 pt scale, higher score less religious) Mean = 3.9, sd = 1.0 0 (0) N/A N/A
Self-esteem (4 pt scale, higher score lower self-esteem) Mean = 2.0, sd = 0.5 25 (0.5) Mean substitution by school and by gender Some pupils did not like there being no 'unsure' but that is the standard way to ask the questions.
Attitude to school (5 pt scale, higher score poorer attitudes) Mean = 2.6, sd = 1.0 26 (0.5) Mean substitution by school and by gender No clear reason
Teacher-pupil relationships (5 pt scale, higher score poorer relationships) Mean = 2.8, sd = 0.9 60 (1.2) Mean substitution by school and by gender No clear reason