Each indicator is composed of one or more measures which will show trends over time. Many indicators have a single measure, but where it does not make sense to combine data, the indicator will have more than one measure. Each measure is summarised or assessed separately using 4 categories.
These categories show how the measures are changing 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 assessment categories 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. The four categories are:
- 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.
An assessment result of ‘Improving’ or ‘Deteriorating’ is made only when there is sufficient confidence that the change is statistically significant and not simply a product of random fluctuations. When there is insufficient confidence that a change has taken place the ‘Little or no overall change’ assessment result is used.
Where there is insufficient data to make an assessment, for example, when the time series is too short, or where there is no data available to compare, this is indicated by the ‘Insufficient or no comparable data’ category.
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 3%, unless noted otherwise. Where the data allow it, a 3-year average is used to calculate the base year; this reduces the likelihood of any unusual years unduly influencing the assessment.
Where an indicator value has changed by less than the threshold of 3%, the ‘Little or no overall change’ assessment result is used. The choice of 3% as the threshold is arbitrary but is used across other government indicators; the use of this approach is kept under review.
The assessment results only reflect the overall change in the measure from the base to latest year and do not reflect fluctuations during the intervening years.
Where sufficient data are available, 2 assessment periods have been used:
- Long term – an assessment of change since the earliest date for which data are available, although if the time series is for less than 10 years a long-term assessment is not made.
- Short term – an assessment of change over the latest 5 years.
In 2 cases (indicators C3a and C3b), the short-term assessments have been carried out over a 6-year time period. This is because the assessments on which the indicators are based are only submitted to the European Union (EU) once every 6 years. For both long-term and short-term assessments, the years over which the assessment is undertaken are stated in the assessment table and/or accompanying notes.
Where the data allow, the individual indicators also have a third marker showing the direction of change in the latest year. This period is too short to make any meaningful assessment. However, when the change exceeds a 1% threshold, the direction is given simply as an acknowledgement of very recent trends and as a possible early indication of emerging trends.