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[Graph]
Figure 1
These plots are on semilog scales, which means that a straight line
connects data that has a constant percentage change each year. The raw
data can be fitted rather well by the three straight lines (although
surely by other ways as well) indicating (1) that the number in the sample
sober between 1 and 2 years is 38% of the number sober less than a year;
(2) that the number sober 2, 3, or 4 years is about 76% of the number
sober one less year, and that the number sober 5, 6, 7 or more years is
about 84% of the number sober one less year.
It is natural to think of these percentages as survival rates of members
in the Fellowship, but a little thought suggests that they must be
modified in at least two ways. The most important way can be illustrated
by the following example: those in the sample that are sober ten years
must have come into the fellowship at least ten years previously.
(Neglecting differences from any that might have been sober before they
came to A.A.) Thus they were part of a much smaller membership than
the 1989 sample represents (the membership in 1979 was 45% as large as the
membership in 1989), and they represent a larger percentage of that 1979
group than of the 1989 sample which the raw data give. The former will
therefore be the meaningful survival percentage for that group. And, of
course, similarly for those sober any other number of years.
Among the approximations that are involved in this modification of the
data of the 1989 survey are that many of those sober ten years may have
been in the Fellowship a longer period of time, and some may have been
sober before coming to the Fellowship. These two effects will, to some
extent, cancel each other. Another approximation is that the group of
newcomers in any year is proportional to the total membership that year.
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