Page 34 - 20dynamics of cancer

AGE OF CANCER INCIDENCE 19

1EPI *IQEPI
E F
-RGMHIRGI

G H
%GGIPIVEXMSR

z
z
I J
%GGIPIVEXMSR

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z
%KI

Figure 2.1 Age-specific cancer incidence and acceleration. (a,b) Age-specific
incidence, the number of cancer cases for each age per 100,000 population on
a log-log scale, aggregated over all types of cancer. For example, a value of 3 on
3
the y axis corresponds to 10 = 1, 000 cancer cases per year, or 1 percent of the
population of a given age. Circles show the data, which are tabulated in five-year
intervals. I fit curves to the data with the smooth.spline function of the R statis-
tical language, using a smoothing parameter of 0.4 (R Development Core Team
2004). (c,d) Age-specific acceleration, which is the slope (derivative) of the age-
specific incidence plot at each age. I obtained the derivatives from the smoothed
splines fit in the incidence plots. (e,f) The acceleration plots in the row above
are transformed by changing the age axis to a linear scale to spread the ages
more evenly. Data are for individuals classified racially as whites in the SEER
database for USA cancer incidence, years 1973–2001 (http://seer.cancer.gov/).

2.1 Incidence and Acceleration

Age-specific incidence is the number of cancer cases per year in a
particular age group divided by the number of people in that age group.
Figure 2.1a,b shows age-specific incidence for USA males and females