Background: previous findings from studies on the acute effects of dru
gs indicate that older subjects report less change on visual analogue
scales than do younger subjects, when the observed drug effects on obj
ective performance measures are as great or greater. Aim: to validate
the use of visual analogue scales independently of internal perception
s. Subjects and methods: 50 younger and 50 older subjects rated attrib
utes of four animals-tortoise, crow, tiger and wasp-on a series of 10
cm lines. The attributes rated included physical qualities (size, nois
e) and psychological aspects (danger). Results: ratings were generally
similar for the two groups, although older subjects tended to rate sl
ightly greater differences between animals, but the variability was al
so slightly greater. Thus the mean difference between tiger and wasp f
or size was 60.1 (SD 15.6) in the younger group and 68.8 (SD 18.4) in
the older group. Conclusions: these results support the validity of th
e use of visual analogue scales in both groups. Explanations for the p
reviously observed discrepancy may need to be sought in terms of an ef
fect of age on the perception of internal changes rather than on any d
ifference in the use of the scales.