Each indicator is composed of one or more measures that show
trends over time. Many indicators have a single measure, but
where data cannot be combined logically, the indicator will have
more than one measure. Each measure is summarised or assessed
separately using a set of ‘traffic lights’. The traffic
lights show ‘change over time’. They do not show whether the
measure has reached any published or implied targets, or indeed
whether the status is ‘good’ or ‘bad’, although where targets have
been set, these are identified in the indicator text.
The traffic lights are determined by identifying the period over
which the change is to be assessed and comparing the value of the
measure in the base or start year with the value in the end
Little or no overall change
Insufficient or no comparable data
Where possible the assessment has been made by evaluating trends
using statistical analysis techniques. The assessment may be
made by Defra statisticians in collaboration with the data
providers, or undertaken by the data providers themselves. A
green or red traffic light is only applied when there is sufficient
confidence that the change is statistically significant and not
simply a product of random fluctuations.
For some indicators, it is not possible to formally determine
statistical significance and in such cases the assessment has been
made by comparing the difference between the value of the measure
in the base or start year and the value in the end year
against a ‘rule of thumb’ threshold. The standard threshold
used is three per cent, unless noted otherwise. Where the
data allow it, a three-year average is used to calculate the
base year, to reduce the likelihood of any unusual year(s) unduly
influencing the assessment. Where an indicator value has
changed by less than the threshold of three per cent, the
traffic light has been set at amber. The choice of three per
cent as the threshold is arbitrary, but is commonly used
across other Government indicators; use of this approach is
kept under review.
The traffic lights only reflect the overall
change in the measure from the base to latest year and do not
reflect fluctuations during the intervening years.
Where data are available, two assessment periods have been
- Long-term – an assessment of change since the earliest date for
which data are available, although if the data run is for less than
ten years a long-term assessment is not made.
- Short-term – an assessment of change over the latest five
For both long-term and short-term assessments the years over
which the assessment is undertaken is stated in the assessment
table. The individual indicators also have a
third marker showing the direction of change in the last
year. This period is too short for a meaningful
assessment. However, when it exceeds a one per cent
threshold, the direction of change is given simply as an
acknowledgement of very recent trends and as a possible early
warning of emerging trends.
1 For a very
few indicators, the short-term change is over a longer time-period
as a result of the frequency of update of the data upon which the
indicators are based. Thus indicators C3a, C3b and C9b have
a six year short-term assessment.