J Neurol (2012) 259:1793–1800 Table 3 Intraclass correlation coefﬁcients between self and proxy scores for the HDQoL Speciﬁc and Summary Scales: whole sample and HD stage subgroups Whole sample (n = 105) Early HD (n = 36) Moderate HD (n = 18) Advanced HD (n = 50) ICC 0.79 0.74 0.71 0.88 0.73 0.75 0.85 (95% CI) (0.71–0.85) (0.63–0.81) (0.60–0.79) (0.84–0.92) (0.63–0.81) (0.65–0.82) (0.79–0.90) ICC 0.78 0.83 0.76 0.87 0.56 0.63 0.81 (95% CI) (0.61–0.88) (0.69–0.91) (0.58–0.87) (0.77–0.93) (0.29–0.75) (0.39–0.79) (0.65–0.90) ICC -0.03 0.49 0.48 0.24 0.46 0.65 0.37 (95% CI) (-0.47 to 0.42) (0.05 to 0.77) (0.04 to 0.76) (-0.23 to 0.63) (0.02 to 0.76) (-0.28 to 0.85) (-0.09 to 0.70) ICC 0.61 0.77 0.74 0.81 0.76 0.59 0.81 (95% CI) (0.40–0.76) (0.63–0.86) (0.59–0.85) (0.69–0.89) (0.61–0.85) (0.37–0.74) (0.69–0.89) HD Huntington’s disease, ICC intraclass correlation coefﬁcient, CI conﬁdence interval, HDQoL Huntington’s disease health-related quality of life questionnaire 1798 HDQoL Speciﬁc Scales Cognitive Hopes and Worries Services Physical and Functional Mood State Self and Vitality Summary Scale disease-speciﬁc questionnaires are generally moderate to high, and when discrepant, proxies often provide poorer QoL ratings than patients [30] [33]. Our data are consistent with the literature, but it is notable that proxies rated patients’ Speciﬁc Hope and Worries Scale score as better rather than worse than patients’ own ratings. This dimen- sion may be particularly difﬁcult for proxies to gauge as it is perhaps even more internal than other psychosocial dimensions, which can garner lower agreement than more objective physical dimensions [32]. When patient–proxy agreement is examined across dis- ease severity, the Early and Advanced subgroups showed substantial to excellent agreement on the Summary Score as well as for the Speciﬁc Scale scores. In both subgroups, the highest ICC values emerged on the most ‘objective’, observable scale—Speciﬁc Physical and Functional—as has often been reported elsewhere [33]. Yet even the more ‘subjective’ scales such as Speciﬁc Hopes and Worries, or Speciﬁc Mood State, yielded substantial ICCs. This may reﬂect the fact that proxies were long-term companions or close family members who typically show better agreement than unrelated healthcare providers [17, 34]. The HDQoL showed good patient–proxy agreement, not only with early HD patients who could validly assess their own HrQoL, but also with Advanced HD patients who usually have physical or cognitive barriers to self-reporting. Good proxy–patient agreement in the Advanced group was not merely an artefact of proxies assisting with questionnaire completion, because agreement remained substantial even after excluding patients who received assistance. This is in contrast to poorer agreement reported for more advanced stage Alzheimer’s and Parkinson’s disease patients [15–17]. To conﬁrm these postal study results, further investigation where question- naire completion is fully monitored would be useful. For moderate Stage 2 and 3 patients, patient–proxy agreement was moderate to poor. The QoL cancer severity 123 literature reports a similar pattern of results where larger patient–proxy discrepancies were more frequent for patients who were slightly and moderately affected [33], rather than at extreme ends of the spectrum. This may be due to greater scope for variability in ratings of patients and proxies at an intermediate level of disease manifestation. Progression of HD is suggested to be fastest, more variable and diverse in the moderate stages, compared to early or advanced stages of the disease [35]. Therefore, patients with moderate HD might be the most heterogeneous group and most changeable over time, making it hard for proxies to form stable judgements. Furthermore, the moderate stages may be particularly complex for patients, who are beginning to experience a physical and psychological decline which both they and their family have long drea- ded. They may be anxious about other people’s attitudes, or wrongly believe that transient difﬁculties are signs of HD, as we have previously found [36]. Some proxies may ﬁnd it hard to communicate with patients and understand their subtle and ﬂuctuating symptoms at this stage, and our analysis hints that this may be particularly true of male proxies. By comparison, advanced-stage patients’ state and relations with carers are more stable, perhaps making it easier for proxies to evaluate HrQoL. It is also worth noting that the ‘proxy–proxy’ perspective adopted here—where proxies were encouraged to use their own viewpoint, rather than explicitly trying to ‘simulate’ the patient’s feelings— can lead to genuine differences between proxy and patient views of HrQoL [30]. We examined factors that might inﬂuence proxies’ tendency to over- or under-rate HrQoL. Previous studies have suggested that proxies’ level of burden, psychosocial stress and amount of time they spend with patients could moderate their assessment [1, 37–39]. In the present case, neither proxies’ own physical or psychosocial HrQoL (as putative measures of carer burden), nor their degree of