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Introduction
Cough is the most common symptom of respiratory illness, and the majority of children with isolated chronic cough do not have asthma. 1 2 It is thus not surprising that cough is a commonly used outcome measure in research and clinical studies. 3-5 Chronic cough is related to a variety of aetiologies 6 and may not be categorised into a specific disease process rendering quality of life (QOL) measures for respiratory diseases such as that for asthma unsuitable substitutes for cough research. Disease-specific QOL inventories have been shown to be significantly superior to generic QOL inventories, 7 with cough-specific QOL measures for adults 8 9 showing specificity and sensitivity over generic QOL measures. The inclusion of factors such as urinary incontinence in these adult cough QOL questionnaires, however, makes them clearly inappropriate for paediatrics. Furthermore the importance and relevance of paediatric-specific QOL instruments has been increasingly recognised. 10-12 The adult cough-specific QOL questionnaires, 8 9 13 however, highlighted the need for a cough-specific QOL measure and demonstrated the poor appreciation by physicians of the impact of chronic cough on their patients. 8 9 Our previous studies have confirmed the high burden of parental concern in children with chronic cough. 14 15 We have also shown that our preliminary QOL questionnaire derived from a clinical impact method was internally consistent and valid. 15
As young children are unable to verbally express themselves adequately, it is standard practice for parents to be proxy assessors of their young child's medical condition. 16 Also, parents/carers are themselves affected by their child's medical condition and thus the parents' own QOL is relevant. Thus, QOL measures used in paediatrics concern the parents/carers themselves (such as in the Short Form Health Survey, SF-12 17 ) or are proxy QOL measures (ie, parental perception of their child's illness; eg, Pediatric QOL Inventory 4.0 (PedsQL) 18 ). A third type of QOL measure for use with children combines both, whereby the items include both parental-proxy and parent's QOL measures such as in Juniper's widely used child asthma QOL questionnaire for carers. 16
Valid and clinically relevant outcome measures are essential for clinical research. Current outcome measures for paediatric cough are limited. 2 Indeed we described the first validated paediatric subjective cough system. 19...