Assessing indicators

Each indicator is composed of one or more measures which will 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 year.

	Improving
	Little or no overall change
	Deteriorating
	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, and 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 used:

• Long-term – an assessment of change since the earliest date for which data are available, although if data do not precede 1996 a long-term assessment is not made.
• Short-term – an assessment of change since 2000 (or the closest date for which data are available).

The UK Biodiversity Indicator Steering Group, which reports to senior civil servants in the four countries, is considering adopting a ten year rolling period for the short-term change assessment, which will mean that when 2020 is reached, the assessment will be over the period of the Strategic Plan for Biodiversity 2011–2020.

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.