Chapter 4 - Onset of impairment, Life Opportunities Survey - Wave Two Report, Part 1

Chapter 4 – Onset of Impairment

The results presented in this chapter are for those adults with no impairment at Wave One but reported at least one impairment at Wave Two. These adults will be referred to as ‘onset-acquired’.
The longitudinal data collected by LOS allow changes over time to be observed and an onset rate to be calculated to indicate the proportion of adults who had acquired an impairment between Waves One and Two. Section 4.1 describes the calculation of onset rates. Section 4.2 examines the overall rate of impairment onset for the population, as well as examining whether onset rates vary across demographic characteristics. Section 4.3 then describes the types of impairments experienced by this group at Wave Two.

Onset of Impairment

The onset rate used in this report has been calculated as the percentage of all adults without any impairment at Wave One who became onset-acquired at Wave Two. The overall onset rate was 8 per cent, meaning that of all adults followed up on the LOS who did not report any impairment at Wave One, 8 per cent subsequently reported at least one impairment at Wave Two. At Wave One, 71 per cent of adults reported no impairment.

Due to the longitudinal survey design there is a potential downward bias in the onset rate reported by the LOS. This means that the onset rates presented in this report should be interpreted as providing a lower bound estimate of the transition into impairment (see Section 4.1 for further information).

4.1 Survey design implications for the calculation of an overall onset rate

Calculation of the LOS onset rate at Wave Two was complicated by the use of two different methods of follow-up for sub-samples of adults without impairment at Wave One. As a consequence, there is a potential downward bias in the reported onset rates. At Wave Two, data were collected either via a telephone interview, a face-to-face interview or a combination of the two. As described in the Introduction, a subset of adults without impairments at Wave One were assigned to the “onset-screening” group, who were followed-up prior to Wave Two fieldwork to establish if anyone in their household had acquired an impairment. This telephone interview took place eight months after the Wave One interview. The remainder of adults without impairment at Wave One, who were either in the “control group”, or who were co-residents of adults with impairments or adults in the control group, were followed up with face-to-face interviews 12 months after the Wave One interview¹.

Thus, adults without impairment at Wave One were followed up either eight months after Wave One (if they were in the onset-screening group) or twelve months after Wave One (if they were in the control group or residents of households receiving face-to-face interviews or they live in a household where someone reported an impairment at the telephone interview). Consequently, a proportion of adults without impairment at Wave One (those in the onset-screening group) would have an unknown impairment status 12 months after their Wave One interview because they received a telephone interview eight months after Wave One. It is likely that some proportion of this group would have acquired an impairment in the four months following their Wave Two telephone interview, but as they were not contacted again, an estimate of this proportion is unknown. Due to this reason, the onset rates provided in this report may be lower than the “true” value for the population.

The Wave Two, Part II Report will provide some measure of this downward bias of the onset rate by using the control group to calculate an onset rate which may be closer to the true onset rate for all adults without impairment at Wave One.

It is also possible that there may be ‘interview mode’ effects that influence whether a person is classified as having an impairment or not, depending on whether they received a telephone or face-to-face follow-up interview².  Unfortunately, it is not possible to establish the magnitude of this effect, if it exists at all, within the current survey design.

Despite this potential downward bias in the onset rate estimates, LOS does, however, provide a useful tool for measuring changes in the population with impairments.  It provides a sound and consistent measurement of impairment offsets and, arguably, the reported onset rates indicate a valuable lower bound measure of the transition into impairment – the onset rate.

Notes for 4.1 Survey design implications for the calculation of an overall onset rate

1. Full details of the data collection strategy can be found in the technical report to be published with the Wave Two, Part II report in 2013. Alternatively further details can be found in the Wave Two Interim Technical Report (2.26 Mb Pdf) .
2. A telephone interview that indicates an instance of impairment is not in itself sufficient for the classification of impairment.  The classification of impairment can only be made after a further face-to-face interview at Wave Two.  However, it is possible that the initial telephone follow up might miss some instances of impairment that would have been caught with a face-to-face follow up.  In other words, we are protected against mis-identified onset-acquired cases, but not against onset-acquired cases that were not identified during the telephone interview.

4.2 Onset of impairment by demographic characteristics

Table 4.1 presents the onset rate for different sections of the population based on their Wave One demographic characteristics . Alongside the overall onset rate, rates are provided for adults of working age (16-64) and adults aged 65 or over. The likelihood of becoming onset-acquired was similar for men (7 per cent) and women (8 per cent). Onset rates rose with age, with those aged 65 or over more likely to acquire an impairment than those of working age. More than one in five (23 per cent) adults aged 75 and over without impairment at Wave One subsequently became onset-acquired at Wave Two, compared with less than one in ten (9 per cent) adults aged 45-64, and less than one in twenty of those aged 25 to 44 (4 per cent) and 16 to 24 (3 per cent).

Differences found in the onset rates across regions are likely to be explained by the underlying age distributions for these regions. The age distribution in London is younger than that for all other regions and this is likely to account for the apparent regional difference in the onset rate. In fact, the onset rate for those aged 65 or over living in London is not particularly different to the onset rates for those aged 65 or over living in other regions of Great Britain. In contrast, the onset rate for working age adults living in London appears to be lower than for those living in other regions, across which the onset rate does not differ significantly from each other. 

For adults aged 65 or over, the onset rate was particularly high in the North East, North West and the East Midlands (21, 20 and 22 per cent respectively) and particularly low in Scotland where it was only 12 per cent.

Table 4.1, Onset rates by sex, age, ethnicity and Wave One region of residence at Wave One, and by age

Table source: Office for National Statistics

Table notes:

1. See Appendix 8 for sample size.

Table 4.2 presents the onset rates for different groups of the population based on tenure, education and occupation characteristics at Wave One.

Differences found in the impairment onset rate between tenure are likely to be explained by the underlying age distributions for the different tenure categories. In general, people living in owner-occupier and rent-free accommodation tend to be older than those living in other types of accommodation. The older age distributions, for these two tenure categories, are likely to influence the higher onset rates among people living in owner-occupier and rent-free accommodation (9 per cent and 10 per cent respectively).

Higher levels of education attainment often leads to higher socio-economic levels. This is consistent with the way that the overall onset rate also appears to increase with decreasing levels of socio-economic classification. The onset rates for people in the lower supervisory and technical occupations and semi-routine and routine occupations were the highest.

Table 4.2, Onset rates by tenure, highest qualification and NS-SEC at Wave One, and by age

Table source: Office for National Statistics

Table notes:

1. Qualifications were asked of those aged 16 to 69.
2. Socio-economic classification is based on current occupation. Occupation was also asked of those who are not currently employed but had last worked within the past eight years.
3. ^* Values suppressed due to high standard errors.
4. See Appendix 8 for sample size.

Notes for 4.2 Onset of impairment by demographic characteristics

1. Wave One characteristics are used here due to the complex sampling on LOS. Adults who did not have an impairment at Wave One and who were not selected in Impairment or Control Households, only received a face-to-face interview at Wave Two if they reported an onset of impairment during the keeping in touch exercise prior to Wave Two. It is therefore not possible to report on Wave Two characteristics for these people.

4.3 Impairments reported by adults experiencing onset of impairment at Wave Two

Figure 4.1 shows the number of impairments experienced by onset-acquired adults at Wave Two. Adults who were onset-acquired at Wave Two were most likely to report only one impairment (69 per cent), 19 per cent had two impairments and a further 12 per cent had three or more impairments. Adults of working age were more likely to report just one impairment (73 per cent), than those aged 65 or over (61 per cent). Those aged 65 or over were much more likely to experience onset of three or more impairments (17 per cent) than those of working age (9 per cent).

Figure 4.1 Onset-acquired: Number of impairment reported at Wave Two

Source: Life Opportunities Survey - Office for National Statistics

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Figure 4.2 shows long-term pain, chronic health condition¹, mobility and dexterity² (52, 32, 13 and 9 per cent respectively) were the four most commonly-reported impairments by adults who were onset-acquired at Wave Two. The least commonly reported impairments by adults who had experienced impairment onset were speaking, behavioural or impairment (all 1 per cent). The distribution of impairment types among onset-acquired adults at Wave Two was very similar to both the overall distribution of impairment types found at Wave One and among adults with impairments at both waves (see Figure 2.2) and those who have offset from impairment (see Figure 3.2).

Figure 4.3 shows the impairments experienced by onset-acquired adults split by age. It is interesting to note that while the proportion of adults experiencing onset of the two most common types of impairments (long-term pain and chronic health condition) are similar for adults of working age and those aged 65 or over, a larger proportion of those aged 65 or over than working age adults reported an onset of mobility (25 per cent compared with seven per cent), dexterity (14 per cent compared with 6 per cent), and hearing impairments (12 per cent compared with 5 per cent). On the other hand, a higher percentage of working age adults reported the onset of a mental health condition (10 per cent compared with 2 per cent) and learning (5 per cent compared with 1per cent) impairments than those aged 65 or over.

Figure 4.2 Onset-acquired: Impairment types reported at Wave Two

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Figure 4.3 Onset-acquired: Impairment types reported at Wave Two, by age

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Notes for 4.3 Impairments reported by adults experiencing onset of impairment at Wave Two

1. Chronic Conditions are defined as long-term conditions that have lasted or are expected to last 12 months or more and that have been diagnosed by a health professional. These include but are not limited to: Asthma or severe allergies; Heart condition or disease; Kidney condition or disease; Cancer; Diabetes; Epilepsy; Cerebral Palsy; Spina Bifida; Cystic Fibrosis; Muscular Dystrophy; Migraines; Arthritis or rheumatism; Multiple Sclerosis (MS) ; Paralysis of any kind; and Depression;
2. Respondents were able to report more than one impairment, therefore the percentages may sum to more than 100.

4.4 Severity of impairment reported by onset-acquired adults

The severity of an impairment can by reflected by both the level of difficulty and frequency of the limitation associated with the impairment¹; these factors are used to define impairment. According to the LOS definition, only those respondents who rated their level of pain to be moderate or higher and the frequency of the limitation to be greater than “never” were identified as having that impairment.

In general, adults who were onset-acquired at Wave Two were most likely to rate the severity of their impairments as low in terms of both the level (moderate) and the frequency (rarely or sometimes) of the limitation they experienced.

Tables 4.3 to 4.7 show the severity in terms of limitation and frequency scales for the four most commonly reported impairments by adults who were onset-acquired at Wave Two: long-term pain, chronic health condition, mobility, and dexterity².

For each impairment, the majority of adults (79 per cent or greater for all four impairment types) experienced moderate difficulty, rather than higher levels of difficulty (severe or cannot do) at Wave Two. For each of these four impairments, a large proportion (43 per cent to 52 per cent) of adults also rated the frequency of limitation to be “sometimes”. However, reasonably high percentages of onset-acquired adults of working age also reported frequency of limitation as “often” or “always” (for example 15 per cent of working age adults reported frequency of limitation for long-term pain as “often” and 9 per cent  reported frequency of limitation for long-term pain as “always”), so onset was not limited to only those in the “rarely” and “sometimes” frequency groups.

The proportions of onset-acquired adults reporting moderate or severe difficulty do not appear to be associated with age: the proportions reporting moderate limitation among working age adults was very similar to the proportion of those aged 65 or over reporting the same level of pain, across all four impairment types.

The proportion of adults with onset of a mobility impairment at Wave Two were nearly three times as likely to ‘always’ experience difficulty, compared with onset-acquired adults who had long-term pain (32 per cent compared with 11 per cent).

Adults aged 65 or over who experienced onset of a chronic health condition or a dexterity impairment were more likely to “always” experience difficulty and less likely to “sometimes” experience difficulty than their working age equivalents. For example, among adults who experienced an onset of a chronic health condition, 27 per cent of those aged 65 or over “always” experienced difficulty compared with 13 per cent of working age adults, and 41 per cent of adults aged 65 or over “sometimes” experienced difficulty compared with 55 per cent of adults of working age.

Table 4.3, Onset-acquired: severity of long-term pain at Wave Two, by age

Table source: Office for National Statistics

Table notes:

1. Level of pain for long-term pain is measured by the intensity of pain – “mild”, “moderate”, or “severe”. Under the LOS definition, those who reported moderate or severe levels of pain, and rated the frequency of limitation as “rarely” or above were identified as having long-term pain.

Table 4.4, Onset-acquired: severity of chronic health condition at Wave Two, by age

Table source: Office for National Statistics

Table notes:

1. Response categories for level of difficulty: 1. “No Difficulty”; 2. “Mild Difficulty”; 3. Moderate Difficulty 4; “Severe Difficulty”; and 5. “Cannot Do”; For some impairment types (chronic condition, breathing, learning, intellectual, behavioural, memory, and mental health impairments), the levels range from 1 to 4. For pain, the level of pain is measured by the intensity of the pain experienced: 1.”Mild”; 2.”Moderate”; 3. “Severe”.

Table 4.5, Onset-acquired: severity of mobility impairment at Wave Two, by age

Table source: Office for National Statistics

Table notes:

1. Response categories for level of difficulty: 1. “No Difficulty”; 2. “Mild Difficulty”; 3. Moderate Difficulty 4; “Severe Difficulty”; and 5. “Cannot Do”; For some impairment types (chronic condition, breathing, learning, intellectual, behavioural, memory, and mental health impairments), the levels range from 1 to 4. For pain, the level of pain is measured by the intensity of the pain experienced: 1.”Mild”; 2.”Moderate”; 3. “Severe”.
2. ^*Value suppressed due to small sample size.

Table 4.6, Onset-acquired: severity of dexterity impairment at Wave Two, by age

Table source: Office for National Statistics

Table notes:

1. Response categories for level of difficulty: 1. “No Difficulty”; 2. “Mild Difficulty”; 3. Moderate Difficulty 4; “Severe Difficulty”; and 5. “Cannot Do”; For some impairment types (chronic condition, breathing, learning, intellectual, behavioural, memory, and mental health impairments), the levels range from 1 to 4. For pain, the level of pain is measured by the intensity of the pain experienced: 1.”Mild”; 2.”Moderate”; 3. “Severe”.
2. ^*Value suppressed due to small sample size

4.5 Onset rates of impairment types

Longitudinal data allow onset rates to be calculated for each impairment type. The onset rates used in this report have been calculated as the percentage of all people without any impairment at Wave One, who subsequently reported a specific impairment at Wave Two. Analysis in this section has been restricted to looking at the onset rates for onset-acquired adults. Adults with impairment at both waves can also experience an onset of impairment; these adults are not included in this analysis. The onset rates by impairment types for adults with impairment at both waves can be found in Section 2.3.

Table 4.7 shows that the rate is higher for those aged 65 or over than for working age adults, this is most notable long-term pain (8.8 per cent compared with 3.1 per cent), chronic health condition (5.7 per cent compared with 1.9 per cent), mobility (4.5 per cent compared with 0.4 per cent) and dexterity (2.6 per cent compared with 0.4 per cent) impairments. This is consistent with the pattern seen in Table 4.1.

Table 4.7, Onset-acquired: onset rates by impairment types, and by age

Table source: Office for National Statistics

Table notes:

1. Sample size denotes the number of adults in the sample with no impairment at Wave One.
2. ^* Value suppressed due to small sample size.

4.6 Onset of impairment due to an increase in severity

In order for an adult to be classified as having an impairment, according to the LOS definition, he/she has to report the impairment and experience more than ‘mild’ difficulty and a degree of limitation as a consequence of the impairment. It is therefore possible that some impairment onsets identified at Wave Two may actually be a result of a change in the level of difficulty reported for the impairment from ‘mild’ to more severe levels, rather than the onset of a new previously unreported¹ impairment between Wave One and Two.

For example, an adult may report a dexterity impairment at Wave One, but because the level of difficulty experienced was ‘mild’ he/she was not classified by LOS as an adult with a dexterity impairment. At Wave Two the same adult may again report a dexterity impairment but if by this time the level of difficulty experienced has increased to ‘moderate’ (or above), he/she will be classified by LOS as having a dexterity impairment at Wave Two.

Table 4.8 shows the onset rate for the four most commonly-reported impairment types overall, split by adults who experienced an onset of impairment at Wave Two because the difficulty level experienced increased from ‘mild’ (onset from mild), and by adults who experienced an onset of impairment at Wave Two because they reported that impairment for the first time (complete onset). These figures are presented alongside the overall onset rates from Table 4.7. Corresponding figures for the other impairment or health condition types can be found in Appendix 8.

More than half of adults who experienced onset of a chronic health condition had previously reported mild difficulty associated with this impairment. This indicates that the course of onset for chronic health condition might occur over a long period. In contrast, a lower proportion of dexterity impairment onset can be explained by an increase in the level of difficulty experienced; this could indicate that dexterity impairment develops more quickly than chronic health condition, or that a dexterity impairment is unlikely to cause mild difficulty.

Table 4.8, Onset-Acquired: onset due to an increase from mild difficulty' at Wave One, by age

Table source: Office for National Statistics

Notes for 4.6 Onset of impairment due to an increase in severity

1. LOS collects information about impairments experienced by the respondent at the time of the interview. Respondents may have experienced periods of impairment prior to their participation in LOS that were not recorded at Wave One because the respondent was not experiencing that impairment at that time.

Background notes

1. Details of the policy governing the release of new data are available by visiting www.statisticsauthority.gov.uk/assessment/code-of-practice/index.html or from the Media Relations Office email: media.relations@ons.gsi.gov.uk