Evaluating Patient-Based Outcome Measures - NIHR Health ...

Summary items
Single questionnaire items have an important
role in health care research. They invite respondents
to summarise diverse aspects of their health
status by means of one or a very small number of
questions. The General Household Survey has,
in annual surveys since 1974, used two questions
that together provide an assessment of chronic
illness and disability: ‘Do you have any longstanding
illness or disability?’ and ‘Does this
illness or disability limit your activities in any
way?’ A positive answer to the two questions
provide an indication of chronic disability.
An even simpler summary item is the question used
in the Health Survey for England: ‘How is your
health in general? Would you say it was ‘very good’,
‘good’, ‘fair’, ‘bad’, ‘very bad’?’
The item ‘How would you rate your general
feelings of well-being today’ with answers indicated
on a single visual analogue scale has been
advocated for use in cancer (Gough et al., 1983).
Transition items are another form of summary
health item, in this case asking the respondent to
assess the state of their health currently compared
with a specific point in the past such as their last
clinic visit. Thus a transition item for use in arthritis
asks patients: ‘Thinking of any overall effects your
arthritis may have on you, how would you describe
yourself compared to the last time I interviewed
you in (month)?’ ‘Do you feel you are ‘much better’,
‘slightly better’, ‘the same’, ‘slightly worse’ or
‘much worse’?’ (Fitzpatrick et al., 1993b).
Advantages and disadvantages
The most obvious advantage of all such items is
their brevity. They make the least demands on
respondents’ time. In the case of summary health
items, some have also been used widely and for a
long time on large samples of the general population
so that there is a considerable range of
potential comparable evidence. Despite their
obvious simplicity, there is evidence of summary
item validity; negative answers to such single items
are given by individuals with poorer health (Leavey
and Wilkin, 1988; Anderson et al., 1990). The single
item visual analogue scale for use in cancer was
validated by showing cross-sectional agreement
with more specific and established QoL scores
(Quality of Life Index) in patients with advanced
cancer (Gough et al., 1983). Equally, there is
evidence of the predictive value of single items;
individuals providing negative answers are more
likely to have poorer health in the future (Mossey
and Shapiro, 1982). Idler and Angel (1990) found
that, amongst middle-aged men, self rated health
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status was predictive of mortality over 12 years,
after controlling for its association with medical
diagnoses, demographic variables and health
behaviour. There is also very favourable evidence
of the reproducibility of self-rated health (Lundberg
and Manderbacka, 1996). With regard to
sensitivity to change, a visual analogue item has
been used in a series of randomised controlled
trials of various treatments for breast cancer and
been shown to be a responsive measure of wellbeing
(Hurny et al., 1996). Similarly, transition
items have been shown to have good validity by
producing scores consistent with independent
evidence of the direction of change in health
experienced by respondents between separate
assessments (MacKenzie et al., 1986a; Fitzpatrick
et al., 1993b; Garratt et al., 1994a). In these studies,
patients reporting deterioration or improvement
in relation to a baseline assessment show corresponding
patterns of change in other baseline and
current data on their health (Deyo and Diehl,
1986). As pointed out below amongst the disadvantages,
summary items cannot reveal contradictory
trends in different dimensions of health, for
example an improvement in physical function that
coincides with deteriorating psychological wellbeing.
However by inviting the respondent to
summarise their health, they do offer a potential
method for weighing up the significance of such
contradictory trends. How a sample views a gain
in, say, mobility and reduced pain from an antiarthritic
drug, if it is at a cost in terms of nausea or
some other side-effect, may be best assessed by their
global judgements of overall health change.
Disadvantages of summary and transition items
mainly relate to their brevity. Respondents are
invited to make a summary judgement of dimensions
of health and it is usually not possible to make
more specific inferences about particular aspects of
their health from these answers. The numbers of
distinctions made by the response categories of
simple summary items are few (‘excellent’, ‘good’
etc.) and these may be too crude to detect subtle
but important changes observed by more detailed
assessment (Jenkinson et al., 1994). Because of the
inevitably general nature of such questions, they
may be considered particularly prone to the influence
of expectations, transient aspects of mood,
and variations between respondents in criteria for
answering such questions (Krause and Jay, 1994).
In the context of a trial, investigators are often
interested in opposing trends in different dimensions
of health; for example, improvements in
physical health at the expense of mood. Summary
or transitional items by themselves do not permit
the detection of such trends. There is also evidence
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