Useful definitions

If you have any queries about any of the following please contact the Research Team on 01432 260495 or email researchteam@herefordshire.gov.uk.

Confidence intervals 

When making estimates about a whole population based on a sample of that population, there is a margin of error around those estimates.  Confidence Intervals (C.I.) are used to give an indication of the likely size of this margin.  The smaller the sample size and the greater the degree of variation, the wider the C.I. will be.

Confidence intervals are used as a clear and simple method of determining whether the difference between two groups is “statistically significant”, i.e. whether there is sufficient evidence to suggest that it reflects a real difference in the wider population.  If the confidence intervals of the two comparative sets of data overlap, then the difference is not statistically significant (e.g. Chart A, below).  If the confidence intervals do not overlap, then the difference is statistically significant (e.g. Chart B, below).

Chart demonstrating overlapping and non-overlapping confidence intervals

Depending on the situation, Confidence Intervals may be explicit as in the charts above, or simply be reflected in the commentary, i.e. differences may be highlighted if they are statistically significant and apparent differences not mentioned if they are not statistically significant.

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Medians and quartiles

The median for a dataset is the value such that 50% of the data points are lower and 50% of the data points are higher. It is an overall summary measure that is less affected by the presence of extreme values (outliers) than the mean.

Diagram of quartiles and the median

The lower quartile for a dataset is the value such that 25% of the data is lower and 75% of the data is higher. The upper quartile for a dataset is the value such that 75% of the data is lower and 25% of the data is higher.  The term "quartile" is also used to refer to a range bounded by the quartile values.  For example, saying that a score lies "in the upper quartile" really means it lies in a range bounded by the upper quartile value and the highest score achieved.  Saying it lies "in the second quartile" really means it lies in a range bounded by the median and the upper quartile value.  The "inter-quartile range" is the range of values bounded by the upper and lower quartiles.

Quartiles and medians have been used for two specific purposes:

  • To compare earnings in Herefordshire with those elsewhere at three different points on the earnings distribution e.g. low earners (25% lower quartile), average earners (median) and high earners (25% upper decile).
  • To compare performance in Herefordshire with all English Authorities. Here the terms top quartile and bottom quartile have been used.
    • If high values of a performance indicator are desired:
      the top quartile of authorities equates to the upper quartile of the dataset
      the bottom quartile of authorities equates to the lower quartile of the dataset.
    • If low values of a performance indicator are desired:
      the top quartile of authorities equates to the lower quartile of the dataset
      the bottom of authorities quartile equates to the upper quartile of the dataset.
    • In some cases, the terms "best" and "worst" are used in preference to "upper / lower" or "top / bottom", to avoid confusion.

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Output areas geographies (OA, LSOA and MSOA)

Statistics relating to small areas have traditionally been released on a ward basis but this has proved unsatisfactory for data dissemination.  Boundaries change periodically so gathering data over time is difficult.  Also ward population sizes vary enormously and wards are designed for electoral representation rather than representing the demography of an area, so they are often inappropriate for other use.  The Office for National Statistics has therefore produced different levels of "output area geographies" as outlined in the table:

Table showing output area geography definitions

Official statistics are increasingly being produced for these geographies, particularly LSOAs.  More details on output area geographies in Herefordshire can be found in a QER article from May 2004, which includes an explanation of how local names for LSOAs were devised to give more of an indication of the area covered than the generic codes allocated by ONS.  Please follow this link for a map of Lower Super Output Areas.

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Rural urban classifications

Rural and urban classifications are the product of a project commissioned jointly by the Office for National Statistics (ONS), the Department for Environment, Food and Rural Affairs (Defra), the Office of the Deputy Prime Minister (ODPM), the Countryside Agency (CA) and the Welsh Assembly Government to create a new settlement-based definition of urban and rural areas.

In 2004, classifications were published for all Census Output Areas, Lower Super Output Areas (LSOAs) and wards in England & Wales by settlement form and sparsity.  The categories used are:

  • Urban
  • Rural
    • Rural town (town and fringe)
    • Rural village
    • Rural dispersed (hamlets and isolated dwellings)

Each of these categories is then divided into "sparse" and "less sparse".  Settlements of 10,000 people or more are considered urban.  Hereford, Leominster and Ross-on-Wye fall into this category.  The remaining market towns (Kington, Bromyard and Ledbury) are classified as "rural towns".

Following the initial classification of Output Areas, a classification of Local Authority areas was initiated by Defra.  This classified Local Authorities as either major urban, large urban, other urban, significant rural, rural-50 or rural-80.  Herefordshire is classified as rural-50; between 50% and 80% of the local authority's population live in a rural settlement.

More details of the methodology and the picture in Herefordshire can be seen in a QER article from August 2004.  A guide to the methodology is also available on the ONS website.

The rural nature of Herefordshire can be seen in the map below.  You may notice a rogue urban area just north-east of Ledbury - it seems likely that when classifications were made, the Malvern Hills were not taken into account, so villages in the Colwall area may have been seen as suburbs of Malvern.

Map 1. Rurality of Herefordshire at Output Area level
Map 1: Rurality of Herefordshire at Output Area level

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Last updated: 21 October 2011