This section covers the procedures used during the data processing stage. For variables that had to be derived from responses to questions, more detailed explanations are provided.
Appendix F contains the full data specification that was followed in the data processing. Along with the question number and variable name, it shows the base for each question and rules that were applied when editing the data; for example, how missing values were treated and what happened when pupils did not follow the survey routing correctly.
Specification of key derived variables
Scottish Index of Multiple Deprivation and urban/rural classification
The Scottish Index of Multiple Deprivation ( SIMD) is a scale used to determine the relative deprivation of small areas across Scotland. An aggregate score is reached by combining 38 indicators from seven domains: current income; employment; health; education, skills and training; housing; geographic access to services; and crime. Postcodes were collected from pupils to establish the SIMD rank of the areas they lived in using the 2012 version. This was reported in quintiles, with 1 being the 20% most deprived areas and 5 being the 20% least deprived areas.
Overall, 44% of pupils (n=7,375) who returned questionnaires did not provide information on their postcode or gave incomplete postcode information. Complete postcode information is important because it is used to obtain scores for the SIMD. Due to the high number of pupils with missing postcode information, missing postcodes were imputed by sorting the data by class within schools. If a postcode was missing, the postcode of the preceding person was copied, provided they were in the same class. This allowed all pupils to be included in the SIMD analysis.
Had imputation not been conducted on postcodes, a large number of pupils in the most deprived areas would have been excluded from the deprivation analysis, leaving small base sizes. The fact that base sizes are increased as a result of the imputation reduces the chance of a Type II error  .
The Goodman Strengths and Difficulties Questionnaire ( SDQ) was used to explore the relationship between substance use and mental health. The 'Strengths and Difficulties Questionnaire' was designed by Robert Goodman (1997) and is widely used by
researchers, clinicians and education professionals. The questionnaire comprises 25 questions that are grouped into five scales, with each scale including five questions. The scales are:
- emotional symptoms
- conduct problems
- peer relationship problems
- pro-social behaviour
Information on how to score the self-completed SDQ was obtained from the website http://www.sdqinfo.com . For each item in each of the five scales, the value of the responses 'Not true,' 'Somewhat true,' and 'Certainly true' are assigned a value from 0 to 2 (See Table 12). A total score of 0 through 10 is possible for each of the five scales.
Table 12 Values assigned to each item in each scale of the SDQ
|Variable name||Not True||Somewhat True||Certainly True|
|Emotional Symptoms Scale|
|I get a lot of headaches, stomach aches or sickness||somatic||0||1||2|
|I worry a lot||worries||0||1||2|
|I am often unhappy, downhearted or tearful||unhappy||0||1||2|
|I am nervous in new situations. I easily lose confidence||clingy||0||1||2|
|I have many fears, I am easily scared||afraid||0||1||2|
|Conduct Problems Scale|
|I get very angry and often lose my temper||tantrum||0||1||2|
|I usually do as I am told||obeys||2||1||0|
|I fight a lot. I can make other people do what I want||fights||0||1||2|
|I am often accused of lying or cheating||lies||0||1||2|
|I take things that are not mine from home, school or elsewhere||steals||0||1||2|
|I am restless. I cannot stay still for long||restles||0||1||2|
|I am constantly fidgeting or squirming||fidgety||0||1||2|
|I am easily distracted. I find it difficult to concentrate||distrac||0||1||2|
|I think before I do things||reflect||2||1||0|
|I finish the work I am doing. My attention is good||attends||2||1||0|
|Peer Problems Scale|
|I am usually on my own. I generally play alone or keep to myself||loner||0||1||2|
|I have one good friend or more||friend||2||1||0|
|Other people my age generally like me||popular||2||1||0|
|Other children or young people pick on me or bully me||bullied||0||1||2|
|I get on better with adults than with people my own age||oldbest||0||1||2|
|I try to be nice to other people. I care about their feelings||consid||0||1||2|
|I usually share with others (food, games, pens etc.)||shares||0||1||2|
|I am helpful if someone is hurt, upset or feeling ill||caring||0||1||2|
|I am kind to younger children||kind||0||1||2|
|I often volunteer to help others (parents, teachers, children)||helpout||0||1||2|
Overall scores were summed for each of the five scales. Total Difficulties scores were also calculated as an overall measure of psychiatric health by summing the scores for Emotional Symptoms, Conduct Problems, Hyperactivity and Peer Problems, but excluding scores for Pro-Social Behaviour. The range of possible Total Difficulties score ranges from 0 to 40.
Some pupils did not answer one or more of the 25 SDQ items. To be able to calculate a score for each scale, pupils had to answer at least three out of the five items in that scale. For example, if a pupil did not answer three or more of the five items on Emotional Symptoms, an Emotional Symptoms score could not be calculated for that pupil. This same pupil may have answered all of the items in the Conduct Problems scales, and in this case, would have a Conduct Problems score. Total Difficulties scores were only calculated for pupils who had scores for each of the four components in the Total Difficulties score.
Scores for each of the five scales and the Total Difficulties score were grouped into categories of Normal, Borderline, and Abnormal (Table 13). These groupings are used in psychiatry to aid in identification of pupils who are likely to have mental health disorders.
Table 13: Strengths and difficulties scoring
|Total difficulties score||0-15||16-19||20-40|
|Peer relationship problems||0-3||4-5||6-10|
Since 2010 the survey has included the Warwick-Edinburgh Mental Well-being Scale ( WEMWBS). Developed as a tool for measuring mental well-being at a population level, the scale comprises 14 positively worded statements that relate to an individual's state of mental well-being (thoughts and feelings). Pupils were asked to indicate how often they had had such thoughts and feelings over the last two weeks.
The overall score was calculated by totalling the scores for each item (minimum possible score was 14 and the maximum was 70). The higher a person's score, the better their level of mental well-being. The mean was used as a measure of the average score and to compare different groups. Scores were calculated for pupils who gave a valid response to each of the 14 questions.
A variable on family structure (famstat) was computed for inclusion in a small number of tables in the National Overview and topic reports. This variable represents pupils' family structures in their main home only, and does not include information about a second home, if one exists. In the family structure variable, pupils with a 'single parent' live with their own mother or father, pupils with a 'step-parent' live with one of their own parents and one step-parent, pupils with 'both parents' live with both of their own parents, and pupils with an 'other' family structure do not live with either of their own parents and may live with foster parents, grandparents, older siblings, in a residential care home, or with other family members not represented. There were 505 pupils for whom there was no reported family information. These pupils have been excluded from analysis involving the family structure variable.
Classification of smoking status
Pupils were classified as 'regular smokers' (defined as usually smoking at least one cigarette a week), 'occasional smokers' (defined as currently smoking but less than one cigarette a week) or 'non-smokers' (pupils who had never smoked or who were not current smokers) using a variable (smokstat) derived from question 8 of the questionnaire.
As not all pupils responded to Question 8, it was not possible to classify all pupils as regular smokers, occasional smokers or non-smokers. Pupils who could not be classified were excluded from the tables that use smoking status as an investigatory variable. However, the pupils with unknown smoking status were included in the 'all pupils' category.
Classification of parents' and siblings' smoking status
Parents' smoking status was derived from responses to question 23. The variable 'parsmoke' includes pupils whose parents do not smoke daily, who have at least one parent who smokes daily, and those who do not see either parent. The variable has a high number of missing values because pupils who say their parents (or one parent) smoke occasionally are excluded, as are pupils who do not know the smoking status of their parents.
Whether or not pupils' siblings smoke was also derived from question 23. This variable, 'sibsmoke' was derived in the same way as 'parsmoke,' and thus has the same limitations of not including information on pupils whose siblings smoke occasionally or pupils who do not know their siblings' smoking status.
A bogus drug 'semeron' was included in the list of drugs presented in questions 49 and 55 in the questionnaire. A variable was derived using question 49 to capture whether or not pupils had taken any drugs in the last month, in the last year, more than a year ago or never.
The analysis was set up to exclude pupils who reported that the only drug they had ever used was semeron from tables that report on the use of any drugs. No pupils reported using semeron and no other drugs.
Pupils who claimed to have taken semeron but also reported taking other drugs were included in the analysis.
A variable was also derived to capture whether or not pupils have ever been offered any drugs listed in question 49. There were no pupils who reported having been offered semeron but no other drug.
Age at which first smoked, drank, got drunk and took drugs
Question 73 asks pupils to report at what age they first smoked a cigarette (more than a puff), drank alcohol (more than a sip), got drunk and used drugs. For consistency with previous waves, ages below five were presumed to be unlikely. Because the SALSUS questionnaires were entered through scanning, it is probable that some values below 4 represent errors where the scanner failed to register the digit 1 preceding the value (i.e., read in 4 instead of 14). Rather than exclude pupils who reported an age between 0 and 4, we chose to add a value of 10 to these ages so as to keep them in the calculations without skewing the averages. This had a minimal effect on the distribution of ages, but enabled more accurate calculation of average ages of first substance use.
Pupils who gave a valid age for first use of a substance but had previously indicated (in other questions) that they had never used this substance were excluded from the analysis.
Calculating paternal and maternal knowledge scores
Pupils' perceptions of their parents' knowledge of their behaviours was assessed in questions 45 and 46 of the questionnaire. Pupils were asked how much they thought their mother and their father knew about five factors relating to their friends and activities:
- 'Who your friends are'
- 'How you spend your money'
- 'Where you are after school'
- 'Where you go at night'
- 'What you do with your free time'.
The response option 'I think s/he knows a lot' was given a value of 2, 'I think s/he knows a little' a value of 1, and 'I don't think s/he knows anything' a value of 0 for each of the 5 items listed above. The values for each of the items were aggregated to give total paternal and maternal scores, represented in the derived variables 'mumscore' and 'dadscore'. These variables have values ranging from 0 to 10. Scores of maternal and paternal knowledge could only be calculated for pupils who answered all of the five items in questions 45 and 46.
Pupils' perceptions of parental knowledge vary by age group and sex. To take account of this variation, paternal and maternal knowledge scores were banded into below median, at median or above median scores separately for each age group: 13 year olds and 15 year olds.