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5 Notes and Definitions
76. The aim of surveys such as the SHCS is to select a sample which is representative of the population as a whole, thus ensuring that any estimates obtained from the survey data are as close as possible to the true population value. Although the SHCS uses a randomly selected sample, it is not necessarily representative of all households. Some households or dwelling types may be over-represented and others may be under-sampled, and response bias will have a further effect (for example non-response households consisting of a young, single male). In general, the smaller the sample size, the greater the likelihood the estimate could be misleading, so care must be taken when using subsets of the survey sample for analysis.
77. The 'paired' (social and physical) survey response rate is about 60%. Although the SHCS is re-weighted to take non-responses into consideration, we cannot be certain that the weighting process correctly represents the profile of the missing households and their residents.
78. Whilst we cannot quantify the extent of bias due to non-response, we can quantify the likely extent of sampling variability by calculating the 'standard error' associated with an estimate. By convention, a '95% confidence interval' is used to demonstrate the variability. On average there is a 1 in 20 chance that the true value will not fall within the given confidence interval or, conversely, there is a 95% chance that the true value will fall within the given confidence interval.
79. Table 32 shows the "95% confidence limits" for estimates for a range of percentages calculated from sub-samples of a range of sizes 28. Note that the confidence limits for estimates of x% and (100-x)% are the same. The interpretation and use of this table are best demonstrated by an example.
80. In Table 15, 29% of detached houses were rated "good" in terms of energy efficiency. To the right of the table it says that the sample size of detached houses was 794. Looking at Table 32, and reading across the 800 row to the 30% column (the nearest to our figures), we get a confidence interval of ±3.6% around the estimate. Thus we can say that we are 95% confident that the true proportion of detached houses with a "good" energy rating lies between 25.4% and 32.6% (29% ± 3.6%).
81. Confidence intervals for the mean NHER and SAP scores cannot be calculated from Table 32, and so are provided explicitly in Table 11, Table 14, Table 16 and Table 17.
82. The median tends to be a better measure of central tendency than the mean for most SHCS results as it is less affected by skewed distributions and the small number of outlying values which naturally occur in the data.
83. Numbers of cases are rounded to the nearest thousand and percentages to the nearest integer. This rounding may mean that in some cases the percentages do not add up to 100. A blank cell represents no survey cases. Zeroes correspond to either a count of less than 500 or a percentage of less than 0.5%.
Table 32: 95% Confidence Limits for estimates based on SHCS sub-samples of various sizes
Sub-sample size
( i.e. the "n=" value corresponding to 100%) | Estimate |
|---|
1% | 2% | 5% | 10% | 15% | 20% | 25% | 30% | 35% | 40% | 45% | |
|---|
or | or | or | or | or | or | or | or | or | or | or | |
|---|
99% | 98% | 95% | 90% | 85% | 80% | 75% | 70% | 65% | 60% | 55% | 50% |
|---|
percentage points ( + / - ) |
|---|
100 | 2.2 | 3.1 | 4.9 | 6.7 | 8.0 | 8.9 | 9.7 | 10.2 | 10.7 | 10.9 | 11.1 | 11.2 |
|---|
150 | 1.8 | 2.6 | 4.0 | 5.5 | 6.5 | 7.3 | 7.9 | 8.4 | 8.7 | 8.9 | 9.1 | 9.1 |
|---|
200 | 1.6 | 2.2 | 3.4 | 4.7 | 5.6 | 6.3 | 6.8 | 7.2 | 7.5 | 7.7 | 7.9 | 7.9 |
|---|
250 | 1.4 | 2.0 | 3.1 | 4.2 | 5.0 | 5.7 | 6.1 | 6.5 | 6.7 | 6.9 | 7.0 | 7.1 |
|---|
300 | 1.3 | 1.8 | 2.8 | 3.9 | 4.6 | 5.2 | 5.6 | 5.9 | 6.2 | 6.3 | 6.4 | 6.5 |
|---|
350 | 1.2 | 1.7 | 2.6 | 3.6 | 4.3 | 4.8 | 5.2 | 5.5 | 5.7 | 5.9 | 5.9 | 6.0 |
|---|
400 | 1.1 | 1.6 | 2.4 | 3.4 | 4.0 | 4.5 | 4.8 | 5.1 | 5.3 | 5.5 | 5.6 | 5.6 |
|---|
450 | 1.0 | 1.5 | 2.3 | 3.2 | 3.8 | 4.2 | 4.6 | 4.8 | 5.0 | 5.2 | 5.2 | 5.3 |
|---|
500 | 1.0 | 1.4 | 2.2 | 3.0 | 3.6 | 4.0 | 4.3 | 4.6 | 4.8 | 4.9 | 5.0 | 5.0 |
|---|
600 | 0.9 | 1.3 | 2.0 | 2.7 | 3.3 | 3.6 | 3.9 | 4.2 | 4.4 | 4.5 | 4.5 | 4.6 |
|---|
700 | 0.8 | 1.2 | 1.8 | 2.5 | 3.0 | 3.4 | 3.7 | 3.9 | 4.0 | 4.1 | 4.2 | 4.2 |
|---|
800 | 0.8 | 1.1 | 1.7 | 2.4 | 2.8 | 3.2 | 3.4 | 3.6 | 3.8 | 3.9 | 3.9 | 3.9 |
|---|
900 | 0.7 | 1.0 | 1.6 | 2.2 | 2.7 | 3.0 | 3.2 | 3.4 | 3.6 | 3.6 | 3.7 | 3.7 |
|---|
1,000 | 0.7 | 1.0 | 1.5 | 2.1 | 2.5 | 2.8 | 3.1 | 3.2 | 3.4 | 3.5 | 3.5 | 3.5 |
|---|
1,100 | 0.7 | 0.9 | 1.5 | 2.0 | 2.4 | 2.7 | 2.9 | 3.1 | 3.2 | 3.3 | 3.4 | 3.4 |
|---|
1,200 | 0.6 | 0.9 | 1.4 | 1.9 | 2.3 | 2.6 | 2.8 | 3.0 | 3.1 | 3.2 | 3.2 | 3.2 |
|---|
1,300 | 0.6 | 0.9 | 1.4 | 1.9 | 2.2 | 2.5 | 2.7 | 2.8 | 3.0 | 3.0 | 3.1 | 3.1 |
|---|
1,400 | 0.6 | 0.8 | 1.3 | 1.8 | 2.1 | 2.4 | 2.6 | 2.7 | 2.8 | 2.9 | 3.0 | 3.0 |
|---|
1,500 | 0.6 | 0.8 | 1.3 | 1.7 | 2.1 | 2.3 | 2.5 | 2.6 | 2.8 | 2.8 | 2.9 | 2.9 |
|---|
1,600 | 0.6 | 0.8 | 1.2 | 1.7 | 2.0 | 2.2 | 2.4 | 2.6 | 2.7 | 2.7 | 2.8 | 2.8 |
|---|
1,700 | 0.5 | 0.8 | 1.2 | 1.6 | 1.9 | 2.2 | 2.3 | 2.5 | 2.6 | 2.7 | 2.7 | 2.7 |
|---|
1,800 | 0.5 | 0.7 | 1.1 | 1.6 | 1.9 | 2.1 | 2.3 | 2.4 | 2.5 | 2.6 | 2.6 | 2.6 |
|---|
1,900 | 0.5 | 0.7 | 1.1 | 1.5 | 1.8 | 2.1 | 2.2 | 2.3 | 2.4 | 2.5 | 2.6 | 2.6 |
|---|
2,000 | 0.5 | 0.7 | 1.1 | 1.5 | 1.8 | 2.0 | 2.2 | 2.3 | 2.4 | 2.4 | 2.5 | 2.5 |
|---|
2,100 | 0.5 | 0.7 | 1.1 | 1.5 | 1.7 | 2.0 | 2.1 | 2.2 | 2.3 | 2.4 | 2.4 | 2.4 |
|---|
2,200 | 0.5 | 0.7 | 1.0 | 1.4 | 1.7 | 1.9 | 2.1 | 2.2 | 2.3 | 2.3 | 2.4 | 2.4 |
|---|
2,300 | 0.5 | 0.7 | 1.0 | 1.4 | 1.7 | 1.9 | 2.0 | 2.1 | 2.2 | 2.3 | 2.3 | 2.3 |
|---|
2,400 | 0.5 | 0.6 | 1.0 | 1.4 | 1.6 | 1.8 | 2.0 | 2.1 | 2.2 | 2.2 | 2.3 | 2.3 |
|---|
2,500 | 0.4 | 0.6 | 1.0 | 1.3 | 1.6 | 1.8 | 1.9 | 2.0 | 2.1 | 2.2 | 2.2 | 2.2 |
|---|
2,600 | 0.4 | 0.6 | 1.0 | 1.3 | 1.6 | 1.8 | 1.9 | 2.0 | 2.1 | 2.1 | 2.2 | 2.2 |
|---|
2,700 | 0.4 | 0.6 | 0.9 | 1.3 | 1.5 | 1.7 | 1.9 | 2.0 | 2.1 | 2.1 | 2.1 | 2.2 |
|---|
2,800 | 0.4 | 0.6 | 0.9 | 1.3 | 1.5 | 1.7 | 1.8 | 1.9 | 2.0 | 2.1 | 2.1 | 2.1 |
|---|
2,900 | 0.4 | 0.6 | 0.9 | 1.2 | 1.5 | 1.7 | 1.8 | 1.9 | 2.0 | 2.0 | 2.1 | 2.1 |
|---|
3,000 | 0.4 | 0.6 | 0.9 | 1.2 | 1.5 | 1.6 | 1.8 | 1.9 | 1.9 | 2.0 | 2.0 | 2.0 |
|---|
3,093 | 0.4 | 0.6 | 0.9 | 1.2 | 1.4 | 1.6 | 1.7 | 1.8 | 1.9 | 2.0 | 2.0 | 2.0 |
|---|
3,147 | 0.4 | 0.6 | 0.9 | 1.2 | 1.4 | 1.6 | 1.7 | 1.8 | 1.9 | 2.0 | 2.0 | 2.0 |
|---|
3,679 | 0.4 | 0.5 | 0.8 | 1.1 | 1.3 | 1.5 | 1.6 | 1.7 | 1.8 | 1.8 | 1.8 | 1.8 |
|---|
3,783 | 0.4 | 0.5 | 0.8 | 1.1 | 1.3 | 1.5 | 1.6 | 1.7 | 1.7 | 1.8 | 1.8 | 1.8 |
|---|
15,000 | 0.2 | 0.3 | 0.4 | 0.5 | 0.7 | 0.7 | 0.8 | 0.8 | 0.9 | 0.9 | 0.9 | 0.9 |
|---|
84. The SHCS uses the following definitions of dwelling types:
- Detached house - a house that is free standing with no party walls;
- Semi-detached house - a house that is only attached to one other dwelling, commercial premise etc. The two properties taken together should be detached from any other properties;
- Terraced house - a house forming part of a row of three or more dwellings, commercial premises etc.;
- Tenement flat - a dwelling within a common block of two or more floors (commonly up to five storeys but may be higher in certain circumstances) where some or all of the flats have a shared or common vertical access. The selected dwelling need not share the access, but may be situated within the block with shared/common access (own door flat).
- 4-in-a-block - each flat in a block has its own independent access. Flats on the upper level have an internal or external stair;
- Tower/slab - flats in a high rise (ten or more storeys) or flats where the common circulation is predominantly horizontal (maisonette, balcony or gallery access);
- Flat from a conversion - flats resulting from the conversion of a house only. A flat converted from a non-residential building ( e.g. a warehouse) is classified according to the above flat types.
85. The Bedroom Standard is a recognised measure of overcrowding. It allocates a required number of bedrooms to a household depending on the age, gender and marital status of each occupant. This is then compared with the actual number of bedrooms in the dwelling. If actual number of bedrooms is less than the required number of bedrooms the dwelling is considered to be overcrowded. The allocation of bedrooms is done in the following manner:
- 1 bedroom for each married or co-habiting couple of opposite sex;
- 1 bedroom for each same sex or civil partnership couple;
- 1 bedroom for any other person aged 21 or over;
- 1 bedroom for each pair of adolescents aged 10-20 (single) of the same sex;
- 1 bedroom for each pair of children aged <10 (irrespective of sex);
- Any unpaired person aged 10-20 is paired if possible with a child aged <10 of the same sex. If not possible person is given a separate bedroom as are any unpaired children aged <10.
86. Households are allocated to one of eight types as shown below:
- Single adult: 1 adult of non-pensionable age and no children;
- Small adult: 2 adults of non-pensionable age and no children;
- Single parent: 1 adult of any age and 1 or more children;
- Small family: 2 adults and 1 or 2 children;
- Large family: 2 adults and 3 or more children or 3 or more adults and 1 or more children;
- Large adult: 3 or more adults and no children;
- Older smaller: 2 adults at least one of whom is of pensionable age, and no children;
- Single pensioner: 1 adult of pensionable age and no children.
87. The NHER assessment procedure is not based on what a household actually spends on fuel. It is based on a model (produced by the National Energy Services 29) of the theoretical costs of maintaining a standard heating regime for a standard level of occupancy derived from knowledge of the appliances, fuel sources, insulation, size and dwelling type of the premises. Total energy costs include space and water heating, lighting, standard domestic appliances ( e.g. washing machine) and standing charges. The model contains a factor for local climate variations to take into account differences across the UK. In reality household fuel use may be different to that assumed in the model.
88. Level 0 is the simplest of the four NHER assessment levels. It involves measuring up to 19 items and takes about 5 minutes per dwelling. The SHCS uses an enhanced level 0 assessment which includes many of the items recorded in the level 1 assessment and 1 recorded in the level 2 assessment. At this level the scale does not allow scores for individual dwellings to be quoted, but does give the distribution of NHER across subsets of greater than 100 dwellings and therefore the stock as a whole. For further information see the SHCS 2002 National Report 30 Technical Annex 9.
89. The Standard Assessment Procedure ( SAP) is the UK government's preferred system for rating the energy efficiency of dwellings. It is scaled from 1 (poor) to 100 (excellent). It is based on the total fuel costs for space and water heating per square metre of floor space. However, unlike the NHER, there is no factor to take into account regional variations in climate in the UK. Furthermore it does not consider lighting, domestic appliances and standing charges in its modelling of fuel costs, nor does it include any information on occupancy. The SHCS reports use SAP 2001 to allow comparability between survey years. SAP 2001 has a maximum rating of 120, however the SHCS sets all scores of 100 or above at 100 to ensure consistency.
90. The concept of fuel poverty used in this report is based on a theoretical calculation of how much it would cost to heat a dwelling according to a specified regime 10,11,12. It does not utilise information on how much a household actually spends on fuel. In reality households may choose to heat their dwellings in a different manner to that assumed in the model.
91. Table 33 and Table 34 show how energy prices have increased between May 1996 and May 2007, the latest period for which data is available. Using changes in the index for fuel and light as a broad indicator of changes in fuel prices faced by households it is notable that between 1996 and 2002, when the proportion of households in fuel poverty fell to less than 38% of its 1996 value ( Table 18), the price of fuel and light decreased by 17% in real terms. By 2005 the real price of fuel and light was 15% above its 1996 level and the proportion of fuel poor households was around two thirds of its 1996 level. The real price of fuel and light increased by 24% from May 2005 (the midpoint of the 2004/5 survey year) to May 2006 (the midpoint of the 2005/6 survey year) whereas the overall RPI (Retail Price Index) increase was 3% in the same period.
Table 33: Retail Price Index fuel components, May 1996 to May 2007
| Current fuel price indices |
|---|
Coal and smokeless fuels | Gas | Electricity | Heating oils | Fuel and light | Petrol and oil |
|---|
May-96 | 118.6 | 112.7 | 120.9 | 94.2 | 116.4 | 134.7 |
|---|
May-02 | 139.3 | 114.0 | 105.2 | 117.2 | 111.1 | 182.8 |
|---|
May-03 | 142.2 | 115.5 | 105.9 | 118.6 | 112.2 | 184.3 |
|---|
May-04 | 146.6 | 123.5 | 111.9 | 146.2 | 120.3 | 199.3 |
|---|
May-05 | 163.6 | 139.8 | 123.1 | 172.2 | 134.8 | 209.0 |
|---|
May-06 | 178.5 | 185.2 | 150.1 | 222.0 | 170.2 | 236.1 |
|---|
May-07 | 189.7 | 206.6 | 165.7 | 204.4 | 185.6 | 232.4 |
|---|
% change May-96 to May-06 | 50.5% | 64.4% | 24.2% | 135.6% | 46.2% | 75.3% |
|---|
% change May-02 to May-06 | 28.1% | 62.5% | 42.7% | 89.4% | 53.2% | 29.1% |
|---|
% change May-05 to May-06 | 9.1% | 32.5% | 21.9% | 28.9% | 26.2% | 13.0% |
|---|
Source: DTI Quarterly Energy Prices Tables31
Table 34: Retail Price Index fuel components relative to the GDP deflator, May 1996 to May 2007
| Fuel price index numbers relative to the GDP deflator |
|---|
Coal and smokeless fuels | Gas | Electricity | Heating oils | Fuel and light | Petrol and oil | GDP Deflator |
|---|
May-96 | 96.5 | 91.7 | 98.4 | 76.6 | 94.7 | 109.6 | 122.9 |
|---|
May-02 | 98.4 | 80.6 | 74.3 | 82.8 | 78.5 | 129.2 | 141.5 |
|---|
May-03 | 97.6 | 79.3 | 72.7 | 81.4 | 77.0 | 126.5 | 145.7 |
|---|
May-04 | 98.1 | 82.6 | 74.8 | 97.8 | 80.5 | 133.3 | 149.5 |
|---|
May-05 | 106.9 | 91.3 | 80.4 | 112.5 | 88.0 | 136.5 | 153.1 |
|---|
May-06 | 114.5 | 118.8 | 96.3 | 142.4 | 109.2 | 151.4 | 155.9 |
|---|
May-07 | 117.2 | 127.7 | 102.4 | 126.3 | 114.7 | 143.6 | 161.8 |
|---|
% change May-96 to May-06 | 18.7% | 29.6% | -2.1% | 85.9% | 15.3% | 38.1% | 26.9% |
|---|
% change May-02 to May-06 | 16.4% | 47.4% | 29.6% | 72.0% | 39.1% | 17.2% | 10.2% |
|---|
% change May-05 to May-06 | 7.1% | 30.1% | 19.8% | 26.6% | 24.1% | 10.9% | 1.8% |
|---|
Source: DTI Quarterly Energy Prices Tables32
92. The Tolerable Standard 33 is the minimum condition required by Scottish Law for a dwelling to be habitable. It was introduced in the 1969 Housing Act and was updated in the 1987 and 2001 Acts. The requirements of the Act are that the dwelling:
- Is structurally stable ;
- Is substantially free from rising and penetrating damp;
- Has satisfactory provision for natural and artificial light, for ventilation and for heating;
- Has an adequate piped supply of wholesome water within the house;
- Has a sink provided with a satisfactory supply of hot and cold water within the house;
- Has a WC available for the exclusive use of the occupants of the house suitably located within the house;
- Has a fixed bath/shower and wash-hand basin all with a satisfactory supply of hot and cold water suitably located within the house;
- Has an effective system for the drainage and disposal of foul and surface water;
- Has satisfactory facilities for the cooking of food within the house;
- Has satisfactory access to all external doors and outbuildings.
A failure to meet one or more of these criteria will result in a dwelling being declared Below Tolerable Standard ( BTS). In such cases local authorities are required to act either through closure, demolition or improvement of the dwelling.
93. This report uses three different types of disrepair to describe the state of disrepair of a dwelling:
- Any disrepair - any disrepair, no matter how small, to any element of the dwelling.
- Urgent disrepair - any disrepair which if not rectified would cause the fabric of the building to deteriorate further and/or place the health and safety of the occupier at risk. Urgency of disrepair is only assessed for external and common elements.
- Disrepair to critical elements - any disrepair to the critical elements of the dwelling. The critical elements are those whose condition is central to a dwelling being wind and weather proof, structurally stable and safeguarded against further rapid deterioration. They are as follows:
- Roof covering;
- Roof structure;
- Chimney stacks;
- Flashings;
- Roof gutters and downpipes;
- External walls - finish;
- External walls - structure;
- Access decks and balustrades (common areas - flats only);
- Foundations;
- Damp proof course;
- External doors and windows (dwelling only);
- Doors, screens, windows and roof lights (common areas - flats only);
- Party walls - structure;
- Floor structure;
- Floor finish;
- Dry rot/wet rot.
- Extensive disrepair - is defined as a score of 2 or more on the 10-point repair scale and/or a score of 'medium' or 'renew' on the 5-point repair scale or dry/wet rot in two or more rooms. Extensive disrepair is calculated in order to identify those dwellings where any disrepair present is of a relatively greater severity.
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