Department of Health Sciences
Applied Biostatistics
Exercise: Nasal diamorphine
A multicentre randomised controlled trial was carried out to
compare the effectiveness of nasal diamorphine spray with intramuscular
morphine for analgesia in children and teenagers with acute pain due to a
clinical fracture (BMJ 2001; 322: 261265). In the emergency departments of eight
The authors stated that ‘The distribution of pain scores for the
spray group was lower than that for the intramuscular group at 5 (P=0.04), 10
(P=0.003), and 20 minutes (P=0.002) after treatment, but no different after 30
minutes (P=0.20)’.
(a) What can we conclude
about pain score after 10 minutes?
The pain scores after 30 minutes were as follows:
Pain score 
Nasal diamorphine group 
Intramuscular morphine group 

n (%) 
n (%) 
1 
54 (28) 
48 (25) 
2 
65 (34) 
61 (32) 
3 
36 (19) 
42 (22) 
4 
24 (13) 
23 (12) 
5 
7 (4) 
11 (6) 
6 
5 (3) 
8 (4) 
(b) Is it correct to
conclude that pain scores were no different after 30 minutes?
The following graph was used to present the data on reaction to
the treatment:
(c) What kind of variable
is reaction to the treatment? What does
this graph actually show?
(d) How could the graph be improved?
Solution
(a) What can we
conclude about pain score after 10 minutes?
The difference is highly significant, so we conclude that there is
strong evidence that pain score is reduced when nasal administration is
used.
(b) Is it correct to
conclude that pain scores were no different after 30 minutes? We cannot correctly conclude that pain scores
were no different after 30 minutes. The
difference is not significant, but this means that we have not shown that there
is a difference, not that we have shown that there is no difference. In fact a very small difference can be seen
in the data, the intramuscular group reporting more pain than the nasal group.
(c) What kind of
variable is reaction to the treatment?
We divide the children into separate categories, ‘no discomfort’, ‘mild
reaction’, ‘winced’, ‘cried’, and ‘screamed’.
These have no numerical value, we therefore have a qualitative or
categorical variable. The categories are
clearly ordered, from ‘no discomfort’ to ‘screamed’. We therefore have an ordered categorical
variable, or ordinal variable. What
does this graph actually show? The
graph shows the cumulative reaction. The
first pair of bars shows the proportions reporting no discomfort, the second
pair shows the proportions reporting no discomfort or mild reaction, the third
pair shows no discomfort or mild reaction or winced, and so on. The fifth pair shows all children and is 100%
by definition.
(d) How could the
graph be improved? What we want to
see is the proportions showing each reaction:
This shows
much more clearly that about 20% of the intramuscular group screamed and none
of the nasal group. If we want a
cumulative graph, which I don’t think we do, we should start with screamed,
then screamed or cried, then screamed or cried or winced, etc.:
Now the third
pair of bars show the percentage who winced or worse.