Scottish Government

Increase the proportion of healthy weight children

DESCRIPTION:

This indicator measures the percentage of children aged 2-15 years whose Body Mass Index lies within a healthy range (between the 2nd and 85th percentile of the UK growth reference charts).

The data is gathered via the Scottish Health Survey and is an important high level indicator that encompasses various aspects of lifestyle and wellbeing.

SOURCE:

The Scottish Health Survey (SHeS) is a major population survey based on interviews with adults and children. As part of the survey measurements of interviewees' height and weight are gathered.

The denominator population for the Scottish Health Survey has changed over time. In 1998 3,400 children aged 2-15 had their heights and weights measured. The equivalent figure for 2003 was 2,400. From 2008 to 2012 the annual denominator has ranged from around 1,200 to 1,800.

Healthy weight of children is defined using the UK standard growth reference curves (Cole TJ et al, 1995). The method used corrects for the skewed distribution of BMI values and then assigns each child's BMI to a centile using an age-sex specific lookup of values from the standard reference curves. Children having a BMI that lies between the 2nd and 85th percentile of the reference data are of healthy weight.

The indicator is based on the proportion of children whose BMI is within the healthy range. Data have been measured in 1998, 2003 and annually from 2008 onwards. The baseline year is 2008.

DEFINITIONS:

The Body Mass Index (BMI) is a way of calculating whether a person's weight is appropriate for their height. It is calculated by dividing weight in kilograms by height in metres squared. (kg/m2)

Definitions of healthy weight for children are currently based on the 1990 UK growth reference charts. Children having a BMI that lies between the 2nd and 85th percentile of the reference data are of healthy weight.

BMI values which are more than 7 standard deviations above or below the mean are excluded and treated as outliers.

For the purposes of this indicator Children are defined as those aged 2-15 years.

BASELINE AND PAST TRENDS:

66.2% of children were healthy weight in the baseline year, 2008. The patterns for boys and girls are different, with the majority of the fluctuations over time coming from boys whilst the girls figures have remained relatively stable.

Percentage of children aged 2-15 years whose Body Mass Index lies within a healthy range:

CRITERIA FOR RECENT CHANGE ARROW:

This evaluation is based on: any difference within +/- 2 percentage points of last year's figure suggests that the position is more likely to be maintaining than showing any change. An increase of 2 percentage points or more suggests the position is improving; whereas a decrease of 2 percentage points or more suggests the position is worsening.

For information on general methodological approach, please click here.

FUTURE ISSUES OR REVIEWS:

There have been some changes to the way these figures have been calculated since the 2011 figures were published.  These are as follows:

- the threshold used to differentiate between underweight and healthy weight has been revised from the 5th percentile to the 2nd percentile;

- minor methodological changes have been made in relation to rounding; and

- the range of BMI values at the extreme ends of the distribution which are excluded has been revised from more than 3 standard deviations above or below the mean to more than 7 standard deviations above or below the mean.  This is in recognition of the increase in child obesity since the reference curves were derived and means that some of the previously excluded cases were likely to have been valid BMIs rather than erroneous measures.

These changes were recently made by ISD in their publication of Primary 1 BMI statistics and were largely based on recommendations in a joint statement released by the Scientific Advisory Committee on Nutrition (SACN) and the Royal College of Paediatrics and Child Health (RCPCH) in April 2012. These changes have been mirrored in the Scottish Health Survey to ensure the two sources of child BMI statistics are comparable.

The impact of the revisions is very small and has no bearing on the overall trend.

ASSOCIATED TARGET:

No associated target.