Statistical Methods in Medical Research 4ed

Table 13.4 Efficacy and safety measurements for 10 premature infants receiving treatment for the
prevention of anaemia.
Haemoglobin
(g/dl)
Platelets
( 10 9 =l)
Leucocytes
( 10 9 =l)
Systolic blood
pressure (mmHg)
Age (days): 25 50 25 50 25 50 25 50
Patient number
1 10 5 10 5 700 596 8 0 9 8 71 65
2 10 4 11 4 363 370 16 0 7 6 54 68
3 10 4 10 2 456 645 10 9 16 1 67 69
4 15 6 13 3 260 301 8 6 8 0 77 82
5 16 3 13 9 387 385 8 4 11 1 60 60
6 11 2 10 2 375 431 13 1 12 6 65 75
7 11 8 10 3 472 337 15 0 10 4 71 69
8 12 8 12 8 469 244 16 2 9 9 61 63
9 10 3 9 1 381 505 16 3 13 0 72 70
10 8 9 11 2 526 539 11 8 8 7 57 65
Changes from day 25 to day 50
13.3 Discriminant analysis 475
Haemoglobin Platelets 10 2 log Leucocytes Systolic BP
d1 d2 10, d3 d4
1 0 0 1 0 0 9 6
2 1 0 0 1 3 2 14
3 0 2 1 9 1 7 2
4 2 3 0 4 0 3 5
5 2 4 0 0 1 2 0
6 1 0 0 6 0 2 10
7 1 5 1 4 1 6 2
8 0 0 2 2 2 1 2
9 1 2 1 2 1 0 2
10 2 3 0 1 1 3 8
The purpose of the present analysis is to ask whether there is clear evidence of change
during this later period, and if so to identify its nature.
The lower part of Table 13.4 shows the changes, di, in the variables from 25 to 50 days.
The log transformation for leucocytes was carried out because this variable (particularly
in other data sets) shows positive skewness (see §§2.5 and 10.8). The multiplying factors
for d2 and d3 were introduced, for convenience, to avoid too great a disparity in the ranges
of magnitude of the four measures of change; this scaling does not influence the value of
T 2 in (13.14), or the contributions (bidi) of each variable to it.
As a preliminary step we note the means and standard errors of the four differences,
together with the results of t tests for the hypotheses that the population mean of each
difference is zero: