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GENETICS OF PROGRESSION 151

6
5
4
Incidence 3 2

1
0 (a) (b)
0.5 1.5 2.5 1.25 2.25 3.25

8

R X 10 -5 4

2
(c) (d)
0.5 1.5 2.5 1.25 2.25 3.25
1

$LLA

0
(e) (f)
0.5 1.5 2.5 1.25 2.25 3.25
Age from birth Age from conception

Figure 8.3 Retinoblastoma incidence evaluated with regard to multistage the-
ory. (a and b) Bilateral (solid line) and unilateral (dashed line) incidence of reti-
6
noblastoma per 10 population, shown on a log 10 scale. Description of the data
in Figure 2.6. (c and d) Ratio, R, of unilateral (I U ) to bilateral (I B ) incidence at
each age multiplied by 10 −5 , using the fitted lines in the panels above. (e and f)
Difference in log-log acceleration between unilateral and bilateral cases, which
is the log-log slope of R versus age in Eq. (8.2). The left column shows age from
birth; the right column shows age from conception. Ages measured in years. I
did not use the unilateral data after age 2.5 years (see Figure 8.2), because reti-
nal cell division slows with age, changing a key process that governs incidence.
Without matching data from bilateral cases after 2.5 years, there is no way to
calibrate the effect of slowing cell division on the ratio of unilateral to bilateral
incidence.