In this cross-sectional study of the complex relationship between frailty status and generic QOL in a sample of community-dwelling older outpatients without severe dementia, we used two recently validated assessment tools: the SOF criteria for frailty status, which were demonstrated to be applicable to the whole sample, and the OPQOL. The OPQOL has excellent applicability to cognitively normal subjects , and was shown here to be applicable to people suffering from mild to moderate dementia. The CGA we used included several important social factors determining health in older age, such as recent life events, housing, financial status and social isolation . The high prevalence of frailty, dementia and depression that we found in the sample could be accounted for by the specific setting of the study which involved geriatric outpatients. This hypothesis is supported by the fact that in another recent study on older outpatients with a disability referred to the same geriatric service the prevalence of depressive disorders was found to be even greater (i.e. over 70%) .
Dimensions of QOL associated with frailty status
As far as the correlates of frailty were concerned, consistent with other studies we found that frail subjects reported a worse overall QOL than pre-frail and non-frail subjects [3, 8, 10–14, 36]. Moreover, according to the findings of this study as many as five of the seven dimensions of QOL that we investigated were found to be impaired in frail older participants. This suggests that interventions targeting QOL in frail community-dwelling older outpatients should consider as outcomes, not only health-related QOL, but also other domains of QOL, such as functional independence, psychological well-being, home and neighbourhood, leisure activities and religion. Only the QOL domains of "social relationships and participation" and "financial circumstances" were not significantly different among the three "frailty status" groups.
These findings are consistent with i) the objective variables which were associated with frailty, such as functional dependence, depression and comorbidity, already highlighted by recent studies [3, 10–12, 37], ii) the fact that "frail" participants had higher levels of formal and informal personal support, and iii) the fact that living and financial conditions were similar along the three groups. As far as the latter point is concerned, it is worth noting that the study not only considered family income but also housing tenure which, along with housing value, has been shown to be highly correlated with socioeconomic status in older people . Recent studies have demonstrated that socioeconomic factors have a greater influence on physical disability at younger than older ages  and that among older adults aged 65-74 the association between social inequalities and frailty appears to be mediated by comorbidity . However, even in older subjects socioeconomic inequalities could be responsible for developing functional impairment and certain illnesses . We cannot therefore exclude that, in studying a sample of outpatients, we might have selected a group of community-dwelling older adults with better social and health assistance for whom possible differences in socioeconomic status may have no impact on frailty.
Correlates of QOL according to frailty status
The clinical and functional characteristics independently associated with a worse QOL were: frailty, but with only one of the three SOF criteria being involved, i.e. "reduced energy level"; disability in the "transferring" and "bathing" BADLs and in the "management of money" IADL; depressive status, consistently with available evidence [7, 41, 42]. A possible explanation for the "reduced energy level" SOF item could be an increased production of specific cytokines such as TNF α , which has already been postulated in the pathophysiology of frailty  and could account for the development of a constellation of non-specific symptoms such as weakness, malaise and fatigue ; these could in turn explain a deterioration in QOL. Moreover, closely related to the concept of a "reduced energy level" is that of anergia, namely self-reported lack of energy, which has been shown to be associated with a poorer life satisfaction and a higher mortality risk .
With regard to the relationship between functional status and QOL, Bowling and colleagues reported that perceived self-efficacy discriminated between perceived QOL as "good", or "not good", among people aged 65+ with severe disabilities . The IADL index captures disability at an earlier stage of the disabling process than the BADL index , when the psychological processes of adaptation to disability - discussed in the following paragraph - are not yet fully developed. The management of money is only one of the skills which are lost early in the disabling process [48, 49], but it could have a greater impact on QOL than the loss of other IADLs. This might be because it implies that older people with mild mental impairment perceive less control over their lives since they depend on others in the use of their own money. The relationship between the transferring and bathing BADL abilities and QOL that we found in this study confirms the well-known relevance of limitations in balance, mobility and self-efficacy in affecting QOL [50, 51]. Objective indicators of wealth were not related to QOL not only in our sample but also in other studies, possibly because in older age, when incomes are more levelled, these indicators are less sensitive than subjectively perceived financial circumstances [6, 52].
In "frail" older subjects, a better emotional status and a more advanced age were directly associated with QOL. The association with age suggests that it takes time for an adaptive response to the frailty identity crisis  to occur; this has already been observed in the adaptation to comorbidity and disability by means of the response shift phenomenon [44, 53, 54], a term which has been coined to describe the way the psychological and practical compensatory actions following physical deterioration account for a lack of change in the perceived QOL [46, 53]. In this perspective our findings support the need for research on interventions that address psychological and emotional well-being to improve QOL among frail older adults.
Among "robust" older subjects, the only independent predictor of QOL was the BMI. The association between a higher BMI and a better QOL is supported by recent studies demonstrating that the optimal BMI for the maintenance of functional capacity in older people may be above the normal limit , i.e. between 23 and 30 Kg/m2 [56, 57]. Thus, in robust older people a BMI within this range might also promote a better QOL.
Limitations of the study
Since the sample considered in this study consisted of outpatients, our findings cannot be extended to the entire population of older people living at home. However, it must be noted that frail subjects make larger use of health and community services than subjects who are not frail . Thus, the findings of this study may be useful to promote QOL in the frail elders referred to outpatient services in the community.
The cross-sectional design of the study did not allow us to consider temporary trajectories of QOL. A recent research by Solomon and colleagues showed that individual ratings of QOL are highly variable over time in community-dwelling elderly people with advanced illness (cancer, heart failure and chronic obstructive pulmonary disease) and that declining QOL is not an inevitable consequence of advancing illness . Interestingly, even in this longitudinal study, which did not consider frailty among the covariates, functional status and depression turned out to be determinants of QOL .
Another limitation of our study was the limited size of the subgroups of "frail" and "robust" subjects on which the secondary statistical analyses were performed. These preliminary findings from the secondary analyses will therefore have to be confirmed by longitudinal studies carried out on larger populations of older adults living in the community.