is also important to note that the levels of agreement
between child and other informants are modest [39], especially with regard to the nonobservable aspects of QoL.
Parent/carer ratings may, however, provide an important
alternative perspective to that of the child. However, this
does raise important issues about how information from
different informants is combined or compared.
The developmental aspects of QoL have not been well
studied. It is likely that there will be major agerelated
differences in the way individuals value different aspects of
QoL, the ways in which they can express these and the
ways that these two factors interact. It is inevitable that in
selecting an instrument for a particular age group one will
have to trade-off the age specificity of item content with
the benefits of potential comparability across ages [48]. If
one focuses too much on adapting instruments for use by a
specific age group then it is likely to become difficult to
compare or to pool data collected from subjects of different
ages. On the other hand, if an instrument does not cover the
necessary constructs within an age then the validity of that
instrument will inevitably be compromised. Careful piloting of proposed instruments within the age range to be
studied is therefore essential. There are various ways that
instruments can be tailored to make them more age
appropriate. These include; ensuring that questionnaires are
short and written in simple (age appropriate) language;