The aim of this project is to try to envisage a feasible design or designs so as to enable the ‘bathing experience’ to be as easy and enjoyable as possible for an ‘elderly’ person.Why is this project important?The importance of the growing proportion of ‘elderly’ people as part of the UK population is becoming more and more apparent all the time as the NHS is realising in terms of the shortage of available beds The initial research shows that bathroom products manufacturers are not in tune with this increasing demand.
Elderly people often experience combinations of minor impairments that in sum create significant difficulties and dangers with day to day activities. These conditions include reduced back strength, dexterity, range of motion of limbs and back, balance, tolerance, and vision. A study of injuries in the elderly ranked bathtubs and showers among the six highest priority hazardous (Czaja et al.
, 1982). This ranking was based on the frequency, severity, cost and relative seriousness of injuries for people over 55 years of age compared to people under 55. Mcguire (1971) found that bath tubs and showers were the second most frequently involved home fixtures in injuries.
Even after receiving training in hospital, patients are particularly anxious about tub transfers (Finlayson and Havixbeck, 1992). As well as a site of accidents, the bath tub is often difficult to use by the elderly. A study of 57 disabled people over 74 years of age who were living at home found that 90% of them had difficulty with bathing (Parker and Thorsland, 1991).The Increasing Older Adult PopulationThe need for data when designing for the older adult is becoming more important as the population ageing process continues in the world. The number of people in the world over 65 years of age is predicted to grow by 88% over the next 25 years (almost one million people a month), and approximately one in ten people, or 800 million people, will be over 65 years of age in 2025. Figures for the UK in 1995 showed that 18.
2% of the population was over pensionable age, which translates into over 10.5 million people. The World Health Organisation (WHO) predicts that by 2025 twenty-six countries will have life expectancies of over 80 years of age.
The highest average life expectancy will be 82 years in Iceland, Italy, Japan and Sweden. The UK and the USA have predicted life expectancies of 80 years .Figures 1 and 2 show the world map with indications of the population percentage over 65 years of age in 1997, and the projected world map for the same age group in the year 2025.UK specific projections for population numbers predicts that by the middle of the next century the number of people aged 75 years and above in the UK will have doubled, while the number aged 90 years and above will have more than tripled.
Table 1 shows the estimated figures for the population projections.Given these increases in numbers of older adults, designing to suit the needs of this sector of society is growing in importance. In 1995 nearly 15% of all home accidents involved people aged over 65 years . In the same year it was found (for the sample selected) that 55% of people aged 65-74 and 63% of people aged over 75 had a long-term illness (compared to 31% of people of all ages); 37% of the 65-74 year olds and 48% of the over 75 year olds said this limited their life style [.
In addition, it is estimated that approximately 40% of total hospital and community health service expenditure is on people aged over 65 years of age .These figures highlight the importance of using necessary data on older adults when designing and manufacturing products to be used by them. If data on older adults are not used when products are being designed then a significant proportion of the population may not be accounted for.
As a result this may mean increased injury risk, poor product usability or lower quality of life for older people.Changes with AgeAs a person grows older certain changes may occur which can differentiate them from younger people in terms of certain characteristics or abilities. It is important and necessary that any such changes are accommodated in the design process and in the functioning of products that are to be used by older members of the population. The changes that occur with ageing maybe physical, such as changes in body size and shape, or decreasing maximum strength; changes in performance of sensory functions such as vision and hearing; or they maybe psychological, such as changes in certain cognitive or psychomotor functions. Finally, the effect on the variance or differences observed between people in each of the variables mentioned above maybe due to the ageing process, gender differences or the two factors combined. These issues are discussed in the next sections.Older Adults: Reasons for Differences ?Generally, men and women differ in respect to their relative physical characteristics and abilities.
It is of interest how the ageing process may interact with these differences between the sexes.Recent work by van Beijsterveldt and Steenbekkers  has investigated this area. They found that the effect of ageing is unlikely to explain more than 25% of the variance that they found in the variables measured in their study, with 5% being the more likely figure. Some measured variables did yield relatively high correlations with ageing however, such as the categories of static anthropometry, force exertion, walking speed and step length, auditory and visual capacities, and fine and gross psychomotor capabilities. Essentially, the effect of ageing is that the person is becoming more equal to the level of the weaker younger user.The effect of gender was found to be greater than that of ageing: the differences observed between people in this study were more likely to be due to whether they were male or female rather than 60 or 70 years old. Such a difference is put down to the fact that women generally have smaller and less muscular bodies than men.Some of the variables measured in this study were subject to both age and gender effects, these were mainly force exertions (eg grip strength, push and pull strength) and some anthropometric dimensions (eg stature, standing and sitting eye height).
The different effects that age, gender and the two combined had on the measured variables maybe important considerations in the product design process. The fact that ageing may mean that some older adults are more at the level of the weaker younger user will mean that it is important to design products carefully across the generations, for example, ensuring that the older user can easily open medicine containers while the packaging still remains child-resistant. The effect of gender, especially when combined with the higher proportion of women than men in the older age groups, means that it may well be more important to take into account older female characteristics and capabilities when designing products, especially when requiring design for the weakest or smallest user.
Finally, the joint effects of both age and gender mean that is vitally important to use data for older adults when a product’s design requires the use of a characteristic or capability requiring the use of a variable effected by both factors, for instance gripping strength of the hand.Physical ChangesAnthropometryStudies throughout the world have shown a decline in stature with age after peaking at approximately 25-35 years, with the rate of decline being given as 1-2cm per decade and becoming more rapid with older age [9,10]. Changes in stature maybe the result of:* vertebral compression* vertebral discs changing in height and shape* loss of muscle tone* postural changes.Figure 3 shows stature at different ages in England to illustrate this.Body weight also declines with age, but the pattern of change is not as obvious as for stature. In developed countries, to which most data relate, average body weight of both males and females tends to increase through middle age. For males, weight tends to level off at approximately 65 years of age, and generally then declines; for females, however, the levelling off tends to occur approximately ten years after males, with weight gains frequently being greater. Possible reasons for this weight loss include a reduction in body water content , a decline in muscle mass, and a general decline in general cell mass.
Figure 4 shows the change in body weight with age in England.Range of Motion of JointsIt is generally accepted that the range of motion (ROM) of joints declines with age, and also that, on average, women have a greater range of joint movement than men . Decreases in the mobility of joints may differ throughout the body, ie the mobility of the knee joint may decrease with age at a greater rate than mobility of the neck joint.Steenbekkers  assessed range of motions for various joints, and found significant age effects for the majority of joints ie mobility of the joint decreased with age. Sex effects varied with the joint, however, for instance for the different movements of the head there were few significant differences between males and females, while for the wrist joint there were many significant differences, between the sexes.
StrengthThe general trend for strength is that it declines with age. Strength is at a maximum at 25-30 years, and then tends to decline gradually. It has been reported that at age 51-55 strength is approximately 80% of that at age 31-35 , and at 71-75 years approximately 60% . A 70 year old is only approximately as strong as a 10 year old . Figure 5 illustrates the changes in hand grip strength with age for a USA population.This decrease in strength could be due to different factors. For example, decreased strength maybe due to a primarily age-related change in the number of muscle fibres and their size, with a secondary ageing effect of disuse and therefore atrophy of the muscles due to a sedentary lifestyle . Certain degenerative diseases or age related medical conditions can also lead to reduced physical strength.
Sensory CapabilitiesVisionVisual impairment may take many forms. The most common of these are general degenerative disorders which are associated with the ageing process, most frequently cataracts. The effects of such disorders ranges from a partial loss of visual acuity (or the ability to make distinctions between the smallest forms by means of sight) to the complete loss of sight.The following is a summary of some of the effects that the ageing process may have on vision:* Visual acuity (the ability to discriminate detail) is found to decrease with age from age 15 to 90 years . Individual loss in visual acuity is basically linear with age ie as age increases so visual acuity decreases, as shown in figure 6 (the larger the mean acuity score the smaller the detail that can be discerned by the person).* As visual acuity decreases with age so does the levels of disciminable differences a person can make eg between levels of contrast.
Figure 7 illustrates such a decline for a grey on black contrast at 100 lux illumination level. As can be seen, the point size of the text required for reading ease increases with age (mean values).* Reduction in the visual field tends to be minimal up to the age of 55, but from this age a gradual shrinkage occurs, especially by 75 years.* Dark adaptation varies with age, with the largest effect being for ages 60-89 . On average, a person in this older group will require 240 times as much light to see a target as a younger person.* Increased glare effects exist for older adults, with the most pronounced effects being felt in age group 75-85 years, who need approximately a 50-70 fold increase in target luminance when compared to people aged from 5 to 15 years.* At age 70 it is likely that a loss in colour sensitivity will be evident, while at age 90 one-sixth of people will have 50% inaccurate judgements of colour.
Results from work by Steenbekkers  show that illumination is an important aspect when designing for the readability of text by older people. When illumination levels are low only relatively large letters are readable, regardless of the contrast. Under high illumination levels contrast levels influence readability.
It is important that design professionals take into consideration visually impaired people (of all ages) when designing everyday items and processes. If a “universal” or “design for all” process is used then this will inevitably benefit people who do not have any visual problems also. For example, if an appropriate font size and colour is used against an appropriate background then a normally sighted person will still be able to read easily, but the difference for visually impaired people maybe crucial.It is important that the design process accounts for older people with visual impairments in scenarios such as thew domestic environment, shopping, public transport and so on, to enable them to carry on living and caring for themselves independently without suffering any degradation of living quality that poor design may cause. It should also be noted that older people may still have diminished visual acuity even with the use of corrective devices such as spectacles.
HearingIn much the same way as vision, hearing related problems are among the most commonly occurring changes with ageing. Presbycusis is the term used to describe naturally occurring loss of hearing due to the ageing process. General observations on the changing in auditory functioning are:* There is a loss of hearing sensitivity at the higher frequencies, with loss generally greater among men that women, and with the difference increasing with age .* Figure 8 illustrates the minimum decibel level that can be heard for a 1000 Hz frequency by a Dutch population.As can be seen, as a persons age increases the mean minimum decibel level that can be heard at 1000 Hz frequency also increases.* It would also appear that frequency discrimination declines with age [25,26]; as a person grows older they are less likely to be able to tell the difference between similar sounds.* Auditory temporal resolution (the time scale over which the sounds are heard by the person), which is essential for speech perception and sound localisation, declines with age. For example, Rastatter et al.
 found that speech comprehension was more impaired for old people than young when subjected to time compression, that is, when the sounds came closer together. However, Moore et al.  have concluded, on the basis of their work, that loss of temporal resolution due to ageing is not inevitable.* Work on auditory attention has found that older people may have difficulty in shadowing (repeating the stimulus information that they are presented with) if a competing source of information is presented to the other ear.* This may imply a divided attention deficit, where older people find it difficult to simultaneously focus their attention on more than one stimulus at a time [29,30].* Wickens et al.
 found that older people need more time to switch their attention from ear to ear, missing information that maybe heard by younger people.The general trends in hearing degradation need to be taken into consideration by designers and manufacturers of a wide range of applications. At the one extreme are safety critical systems, such as alarm bells or messages that maybe broadcast in an emergency situation. The potential consequences of not considering the requirements of older adults with hearing difficulties when designing a safety system are all too easy to imagine.
On the other hand, there are design issues relating to ensuring high life quality and independence for a person. Issues here include all aspects of voice communication systems (telephone, radio, television etc) which may be important to an older person with hearing difficulties.It should be noted that it is not advisable to design products and systems and assume that correction devices such as hearing aids will be worn. There is still a greater stigma attached to the wearing of hearing aids compared to spectacles which may mean that some people manage without aids for social reasons (it is also possible that some hearing problems are not correctable even with hearing aids).