Scottish House Condition Survey: Key Findings 2011

6 Notes and Definitions

6.1 Sampling

157. The aim of surveys such as the SHCS is to select a sample which represents well 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. However any randomly chosen sample may give results which, by chance, are either higher or lower than the true value in the population and no two samples are likely to give exactly the same picture of the household population. Response bias will have a further effect (for example non-response households are more likely to consist of a young, single males than the household population as a whole). 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.

158. In 2011, the response rate to the social survey was 69.6%, a full physical survey was then completed at 81.5% of properties where a social survey interview was conducted. The data are re-weighted to take account of unequal probability of selection and non response. While this does not guarantee that we fully reflect the profile of missing households and their residents it does provide more statistically robust estimates. Full details are provided in the Technical Report which accompanies this publication.

6.2 Confidence intervals

159. 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 fall outside the given confidence interval or, conversely, there is a 95% chance that the true value will fall within the given confidence interval.

160. Table 41 shows the 95% confidence limits for estimates for a range of percentages calculated from sub-samples of a range of sizes. 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.

161. In Table 15, 49% 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 792. Looking at Table 41 and reading across the 800 row to the 45% column (the nearest to our figures), we get a confidence interval of '3.5%. Thus we can say that we are 95% confident that the true proportion of detached houses with a 'good' energy rating is between 45.5 and 52.5 (49% ' 3.5%)^[38].

Table 41 95% Confidence Limits for estimates based on SHCS sub-samples of various sizes (without design effects)

Sub-sample size (i.e. the "n=" value corresponding to 100%)	Estimate (lookup to nearest multiple of 5%)
	1%	2%	5%	10%	15%	20%	25%	30%	35%	40%	45%	50%
	or	or	or	or	or	or	or	or	or	or	or
	99%	98%	95%	90%	85%	80%	75%	70%	65%	60%	55%
	percentage points ( + / - )
100	2.0	2.7	4.3	5.9	7.0	7.8	8.5	9.0	9.3	9.6	9.8	9.8
150	1.6	2.2	3.5	4.8	5.7	6.4	6.9	7.3	7.6	7.8	8.0	8.0
200	1.4	1.9	3.0	4.2	4.9	5.5	6.0	6.4	6.6	6.8	6.9	6.9
250	1.2	1.7	2.7	3.7	4.4	5.0	5.4	5.7	5.9	6.1	6.2	6.2
300	1.1	1.6	2.5	3.4	4.0	4.5	4.9	5.2	5.4	5.5	5.6	5.7
350	1.0	1.5	2.3	3.1	3.7	4.2	4.5	4.8	5.0	5.1	5.2	5.2
400	1.0	1.4	2.1	2.9	3.5	3.9	4.2	4.5	4.7	4.8	4.9	4.9
450	0.9	1.3	2.0	2.8	3.3	3.7	4.0	4.2	4.4	4.5	4.6	4.6
500	0.9	1.2	1.9	2.6	3.1	3.5	3.8	4.0	4.2	4.3	4.4	4.4
600	0.8	1.1	1.7	2.4	2.9	3.2	3.5	3.7	3.8	3.9	4.0	4.0
700	0.7	1.0	1.6	2.2	2.6	3.0	3.2	3.4	3.5	3.6	3.7	3.7
800	0.7	1.0	1.5	2.1	2.5	2.8	3.0	3.2	3.3	3.4	3.4	3.5
900	0.7	0.9	1.4	2.0	2.3	2.6	2.8	3.0	3.1	3.2	3.3	3.3
1,000	0.6	0.9	1.4	1.9	2.2	2.5	2.7	2.8	3.0	3.0	3.1	3.1
1,100	0.6	0.8	1.3	1.8	2.1	2.4	2.6	2.7	2.8	2.9	2.9	3.0
1,200	0.6	0.8	1.2	1.7	2.0	2.3	2.5	2.6	2.7	2.8	2.8	2.8
1,300	0.5	0.8	1.2	1.6	1.9	2.2	2.4	2.5	2.6	2.7	2.7	2.7
1,400	0.5	0.7	1.1	1.6	1.9	2.1	2.3	2.4	2.5	2.6	2.6	2.6
1,500	0.5	0.7	1.1	1.5	1.8	2.0	2.2	2.3	2.4	2.5	2.5	2.5
1,600	0.5	0.7	1.1	1.5	1.7	2.0	2.1	2.2	2.3	2.4	2.4	2.5
1,700	0.5	0.7	1.0	1.4	1.7	1.9	2.1	2.2	2.3	2.3	2.4	2.4
1,800	0.5	0.6	1.0	1.4	1.6	1.8	2.0	2.1	2.2	2.3	2.3	2.3
1,900	0.4	0.6	1.0	1.3	1.6	1.8	1.9	2.1	2.1	2.2	2.2	2.2
2,000	0.4	0.6	1.0	1.3	1.6	1.8	1.9	2.0	2.1	2.1	2.2	2.2
2,200	0.4	0.6	0.9	1.3	1.5	1.7	1.8	1.9	2.0	2.0	2.1	2.1
2,400	0.4	0.6	0.9	1.2	1.4	1.6	1.7	1.8	1.9	2.0	2.0	2.0
2,600	0.4	0.5	0.8	1.2	1.4	1.5	1.7	1.8	1.8	1.9	1.9	1.9
2,800	0.4	0.5	0.8	1.1	1.3	1.5	1.6	1.7	1.8	1.8	1.8	1.9
3,000	0.4	0.5	0.8	1.1	1.3	1.4	1.5	1.6	1.7	1.8	1.8	1.8
3,200	0.3	0.5	0.8	1.0	1.2	1.4	1.5	1.6	1.7	1.7	1.7	1.7
3,400	0.3	0.5	0.7	1.0	1.2	1.3	1.5	1.5	1.6	1.6	1.7	1.7
3,600	0.3	0.5	0.7	1.0	1.2	1.3	1.4	1.5	1.6	1.6	1.6	1.6
3,800	0.3	0.4	0.7	1.0	1.1	1.3	1.4	1.5	1.5	1.6	1.6	1.6
4,000	0.3	0.4	0.7	0.9	1.1	1.2	1.3	1.4	1.5	1.5	1.5	1.5

6.3 Design effects

162. However, it is important to adjust these intervals by multiplying by the design effects for the survey. The design effect is the ratio between the variance (average deviation of a set of data points from their mean value) of a variable under the sampling method used (actual) and the variance computed under the assumption of simple random sampling (standard). In short, a design effect of 2 would mean doubling the size of a simple random sample to obtain the same volume of information; a design effect of 0.5 implies the reverse. Design effect adjustments are necessary when adjusting standard errors which are affected by the design and complexity of the survey.

163. Generally speaking, disproportionate stratification and sampling with non-equal probabilities tends to increase standard errors, giving a design effect greater than 1. However, this can be controlled by deliberately over-sampling in stratum where the item of interest is either very rare or variable. The impact of non-response weighting on standard errors tends to be, although with exceptions, comparatively limited. The sampling design of the SHCS meets the criteria above in that disproportionate stratification is applied across the 32 local authority areas with over-sampling of remote rural areas - for example in Shetland and Orkney. As a result, one would expect the design effect to be above 1 although only modestly so.

164. Table 42 shows the design effects for all the SHCS surveys since 1991. When using a mixture of the Physical and Social Survey data, the Physical Survey design effect must be used. The design effects for the 2011 SHCS are 1.12 for the Physical and 1.11 for the Social surveys. When producing estimates at local authority level, no design effect adjustment is necessary for adjusting standard errors because simple (actually equal interval) random sampling was carried out within each local authority.

Table 42 Design Effects for SHCS, 1991-2011

Survey Year	Design Effect
	Physical Weight	Social Weight
1991	1.09	1.09
1996	1.11	1.11
2002	1.11	1.10
2003/04	1.14	1.13
2004/05	1.18	1.17
2005/06	1.14	1.14
2007	1.13	1.11
2008	1.11	1.11
2009	1.09	1.08
2010	1.11	1.1
2011	1.12	1.11

165. The median may be a better measure of central tendency than the mean for some SHCS results as the median is less affected by skewed distributions and the small number of outlying values which naturally occur in the data.

166. 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%.

6.4 Dwelling types

167. 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.

6.5 Household types

168. 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.

6.6 Energy Ratings and Labels

169. The way a building is constructed, insulated, heated and ventilated and thetype of fuel used, all contribute to its energy consumption and carbon emissions. The use of 'energy labels' provides a method of demonstrating the results of complex calculations in an easy-to-understand way.

National Home Energy Rating (NHER)

170. 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) of the theoretical costs ('Total Energy 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 which take into account differences across the UK. In reality household fuel use may be different to that assumed in the model.

171. 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 item recorded in the level 2 assessment. At this level, the scale, used properly, 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 Technical Annex 9^[39].

Standard Assessment Procedures (SAP)

172. SAP is the Government's Standard Assessment Procedure for Energy Rating of Dwellings.

SAP 2005^[40]

173. SAP 2005 is adopted by government as part of the UK national methodology for calculation of the energy performance of buildings.

174. It is scaled from 1 (poor) to 100 (excellent) and reflects the energy cost per square metre for the lighting, space and water heating of a dwelling. SAP takes no account of geography or climatic conditions.

175. It is used to demonstrate compliance with building regulations for dwellings - Part L (England and Wales), Section 6 (Scotland) and Part F (Northern Ireland) - and to provide energy ratings for dwellings.

SAP 2001^[41]

176. The SHCS also includes data on the previous version of SAP (SAP 2001) for comparability with previous surveys. It is scaled from 1 (poor) to 120 (excellent). SAP 2001 only takes space and water heating into account (whereas SAP 2005 also includes lighting). This data is available on request. As with all versions of SAP it takes no account of regional or climatic conditions in its calculation.

Energy Efficiency Ratings (EERs)

177. The Energy Performance Certificate (EPC) is a measure introduced to promote the improvement of energy efficiency of buildings. This is part of a programme of changes being rolled out across Europe to reflect energy efficiency legislation.

178. The EPC Energy Efficiency Rating (EER) letter reflects the SAP 2005 score in a simplified form (Table 43); the higher the rating the more energy efficient the home and the lower the fuel bills should be.

Table 43 EPC Energy Efficiency Rating (EER) and SAP 2005 Ratings

EER	SAP 2005 Rating
A	92 – 100
B	81 – 91
C	69 – 80
D	55 – 68
E	39 – 54
F	21 – 38
G	1 – 20

179. The SHCS emulates RDSAP and EERs from the SAP 2001 scores together with the fuel use based on Table 16 of the SAP 2005 Methodology^[42]. The main differences between the SHCS and EPC methodology lie in the following areas:

• SEDBUK data for boilers was not recorded;
• Extensions were not treated separately;
• Under floor insulation was not recorded - the software determines thickness where required by building standards using age band data;
• Roof/loft insulation location was always assumed to be between joists;
• Meter data was implied from electricity type.

180. However, against these weaknesses, stated quality standards by one protocol organisation are that 95% of EPCs are within +/- 5 SAP points - where SAP ranges within the A-G rating are on average about 14 points.

181. Again, the EER does not reflect climatic differences across Scotland. So a house in Galloway with the same EER rating as a house in Shetland (or in Cornwall) indicates that the quality of the house is similar in respect of EER factors, but does not fully reflect the actual level of energy required for a dwelling in those different climates.

6.7 Energy Prices

182. Figure 11, Table 44 and Table 45 show how energy prices have increased between May 1996 and July 2011 (each is the latest period for which prices are 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 23), the price of fuel and light decreased by 19% in real terms. By 2005 the real price of fuel and light was 7% below 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. Since May 2003 fuel prices have been increasing at a greater rate than GDP, however in 2010 for the first time since May 2003 fuel prices (apart from heating oils) decreased and GDP continued its steady increase of about 2% per annum.

183. Price rises from 2010 to 2011 showed large increases in heating oil costs (44 points), with smaller increases in the costs of gas (11 points) and electricity (7 points).

Table 44 Retail Price Index fuel components, May 1996 to July 2012

	Current fuel price indicies
	Coal and smokeless fuel	Gas	Electricity	Heating oils	Fuel and light	Petrol and oil
May-96	71.0	78.8	97.0	50.0	84.4	63.1
May-02	83.4	79.7	84.4	62.1	80.5	85.6
May-03	85.1	80.7	84.9	62.9	81.4	86.4
May-04	87.8	86.3	89.7	77.5	87.2	93.4
May-05	97.9	97.7	98.8	91.3	97.7	97.9
May-06	106.8	129.4	120.4	117.7	123.4	110.6
Jul-07	112.9	137.1	129.4	113.5	130.3	110.0
Jul-08	131.7	154.8	145.7	203.1	152.8	139.1
Jul-09	157.7	191.2	155.5	117.7	165.5	117.6
Jul-10	156.3	179.4	154.7	154.7	162.1	134.6
Jul-11	165.7	190.4	161.0	198.9	174.2	154.2
Oct-11	176.0	222.7	177.3	196.8	195.4	154.7
Jul-12	172.8	220.4	173.9	193.1	192.5	151.5
Percentage change Jul-10 to Jul-11	6.0%	6.2%	4.0%	28.5%	7.4%	14.5%
Percentage change Jul-10 to Oct-11	12.6%	24.2%	14.6%	27.2%	20.5%	15.0%
Percentage change Jul-11 to Jul-12	4.3%	15.7%	8.0%	-2.9%	10.5%	-1.8%

Source: DECC QEP 2.1.3^[43]

Table 45 Retail Price Index fuel components relative to the GDP deflator, May 1996 to June 2012

	Fuel price index numbers relative to the GDP deflator						GDP Deflator
	Coal and smokeless fuel	Gas	Electricity	Heating oils	Fuel and light	Petrol and oil
May-96	84.8	94.1	115.9	59.7	100.9	75.4	83.7
May-02	89.7	85.8	90.8	66.9	86.7	92.2	92.9
May-03	89.4	84.8	89.2	66.1	85.5	90.7	95.2
May-04	90.2	88.7	92.2	79.7	89.7	96.0	97.3
May-05	98.1	97.9	99.0	91.5	97.9	98.1	99.8
May-06	104.4	126.5	117.7	115.1	120.6	108.1	102.3
Jul-07	107.2	130.2	122.9	107.8	123.7	104.5	105.3
Jul-08	121.6	142.9	134.5	187.5	141.0	128.4	108.3
Jul-09	143.4	173.8	141.4	107.0	150.4	107.0	110.0
Jul-10	138.5	158.9	137.0	137.1	143.6	119.2	112.9
Jul-11	143.1	164.5	139.0	171.8	150.4	133.1	115.8
Oct-11	150.9	191.0	152.1	168.8	167.6	132.7	116.6
Jun-12	145.5	186.0	146.7	159.7	162.2	128.3	118.5
Percentage change Jul-10 to Jul-11	3.3%	3.5%	1.5%	25.3%	4.7%	11.7%	2.6%
Percentage change Jul-10 to Oct-11	9.0%	20.2%	11.0%	23.1%	16.7%	11.3%	3.3%
Percentage change Jul-11 to Jul-12	1.7%	13.1%	5.5%	-7.0%	7.8%	-3.6%	2.3%

Source: DEC QEP 2.1.3

6.8 Fuel Poverty

184. 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 (See footnotes 16, 17 and 18). 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.

6.9 The Tolerable Standard

185. The Tolerable Standard^[44] is the minimum condition required by Scottish Law for a dwelling to be habitable. It was introduced in the 1969 Housing (Scotland) Act and was updated in the 1987, 2001 and 2006 Acts.

186. The Tolerable Standard definition was amended by the Housing (Scotland) Act 2006 to include additional criteria.^[45] As the amendment was not implemented until April 2009 (3 months into the 2009 SHCS fieldwork period), the 2010 report presented the first results based on the amended standard.

A house meets the tolerable standard if it:

• is structurally stable;
• is substantially free from rising or penetrating damp;
• has satisfactory provision for natural and artificial lighting, for ventilation and for heating;
• has satisfactory thermal insulation;
• has an adequate piped supply of wholesome water available within the house;
• has a sink provided with a satisfactory supply of both hot and cold water within the house;
• has a water closet or waterless closet available for the exclusive use of the occupants of the house and suitably located within the house;
• has a fixed bath or shower and a wash-hand basin, each provided with a satisfactory supply of both hot and cold water and suitably located within the house;
• has an effective system for the drainage and disposal of foul and surface water;
• in the case of a house, has a supply of electricity that complies with the relevant requirements in relation to electrical installations for the purposes of that supply;

- 'the electrical installation' is the electrical wiring and associated components and fittings, but excludes equipment and appliances
- 'the relevant requirements' are that the electrical installation is adequate and safe to use

• has satisfactory facilities for the cooking of food within the house; and
• has satisfactory access to all external doors and outbuildings.

187. 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.

188. Most of these criteria have been part of the tolerable standard since its introduction in the 1969 Act. The 2001 Act added the bath / shower and wash-hand basin element. Waterless closets were added by administrative order in 2003. The 2006 Act introduces the most significant change to the criteria - the addition of thermal insulation and electrical installations, and also confirms the addition of waterless closets.

6.10 Disrepair

189. 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: 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.

6.11 Urban Rural Classifications

190. The SHCS uses the 8-category Scottish Executive Urban/Rural Classification 2009-10^[46]. The definitions of the 8 categories are in Table 46 below. When looking for different characteristics in urban and rural areas, it can be more useful to group the 8 categories into 2 gross urban and rural categories. This requires a definition of what constitutes urban and rural. The Scottish Government's core definition of rurality classifies settlements of less than 3,000 people as rural. The 8-category urban/rural classification can be collapsed to the core definition:

• Urban: Large Urban Areas, Other Urban Areas, Accessible Small Towns, Remote Small Towns, Very Remote Small Towns i.e. categories 1 to 5;
• Rural: Accessible Rural, Remote Rural, Very Remote Rural i.e. categories 6 to 8.

191. The full classification can be grouped in differing ways to meet user needs, for example a six category version can be used. In that version, 'Remote Small Towns' and 'Very Remote Small Towns' are grouped into 'Remote Small Towns'; and 'Remote Rural' and 'Very Remote Rural' are grouped into 'Remote Rural'. In this report any urban/rural breakdown uses the core definition of rurality outlined in the previous paragraph.

Table 46 Scottish Government 8 category Urban/Rural Classification 2009-2011

Scottish Government Urban/Rural Classification
1 - Large Urban Areas	Settlements of over 125,000 people.
2 - Other Urban Areas	Settlements of 10,000 to 125,000 people.
3 - Accessible Small Towns	Settlements of between 3,000 and 10,000 people, and within a 30 minute drive time of a Settlement of 10,000 or more.
4 - Remote Small Towns	Settlements of between 3,000 and 10,000 people, and with a drive time between 30 and 60 minutes to a Settlement of 10,000 or more.
5 - Very Remote Small Towns	Settlements of between 3,000 and 10,000 people, and with a drive time of over 60 minutes to a Settlement of 10,000 or more.
6 - Accessible Rural Areas	Areas with a population of less than 3,000 people, and within a drive time of 30 minutes to a Settlement of 10,000 or more.
7 - Remote Rural Areas	Areas with a population of less than 3,000 people, and with a drive time of between 30 and 60 minutes to a Settlement of 10,000 or more.
8 - Very Remote Rural Areas	Areas with a population of less than 3,000 people, and with a drive time of over 60 minutes to a Settlement of 10,000 or more.

6.12 Carbon Dioxide Emissions

192. The estimate of carbon emissions in the SHCS is based on the NHER methodology and is calculated from the theoretical energy used in maintaining the standard regime for a standard level of occupancy, derived from knowledge of the appliances, fuel source, insulation, size and dwelling type of the premises.