from the Wall Street Journal, 12/2/93:

               Good (Hidden) News About the AIDS Epidemic
                       by Robert S. Root-Bernstein

    Statistics of any kind are difficult to interpret, and AIDS 
statistics are no exception.  Indeed, the latest statistics released by 
the Centers for Disease Control are so odd as to be virtually 
indecipherable.  One begins to suspect the difficulties have been 
introduced on purpose.
    On Oct. 30, the CDC released a report contending that AIDS has become 
the top killer of U.S. males age 25 to 44, and the fourth leading killer 
of women in the same age group -- statistics that received wide currency 
in the lead-up to World AIDS Day yesterday.  Although the report states 
clearly that part of the reason for the sudden upsurge in AIDS cases is 
due to a new expanded definition that went into effect a year ago, it 
nontheless presents the data so that the implications of this change are 
far from obvious.
    Between January and September of 1992, 60,656 people were diagnosed 
with AIDS and reported to the CDC.  Between January and September of this 
year, 85,526 new AIDS patients were reported to the CDC, an increase of 
41% from the year-earlier period.  ONe's first impression is that the 
epidemic continues to worsen.
    The CDC report immediately cautions that the huge increase in new 
AIDS cases does not mean that AIDS is mushrooming.  Most of the increase, 
it says, is due to changes in the definition of AIDS that vastly expanded 
the diagnostic criteria at the beginning of this year.  These 
definitional changes were predicted to more than double the number of 
reported cases and, indeed, the number of cases reported under the new 
definition account for more than half of all those reported so far this 
year.
    Interestingly, though, no one seems to have noticed that if the 
number of cases diagnosed under the new definition was to be more than 
twice the number found under the old definition, and AIDS has continued 
to grow at the same rate as before, then the total number of AIDS cases 
reported this year should be not 41% higher than for the same period last 
year but more than 100% higher.  Why the discrepancy?
    Even odder, CDC officials claim that when the new definitional bias 
is taken into account, AIDS is only increasing about 3% to 5% a year, as 
it has been since 1990.  The defintional changes simply allowed many 
people who were going to get AIDS someday (according to the old 
definition) to be diagnosed (and treated) sooner.  That is good for 
people with AIDS, but what does it do to our ability to track the course 
of the epidemic?
    The CDC itself admits that over half of the new cases reported this 
year are due to the new definition: 48,915 of the 85,526.  In other 
words, only 36,611 of the AIDS cases reported so far this year would have 
qualified as AIDS cases according to the old definition.  That is 20,045 
fewer AIDS patients in 1993 that the 60,656 diagnosed during the same 
nine months in 1992.  This is a drop of 33%, not an increase of 3% to 5%.
    So, are AIDS cases increasing steadily at 3% to 5% a year, as the CDC 
claims -- without any apparent justification -- or are they decreasing 
drastically by some 30%?  If all the people who have been diagnosed as 
having AIDS according to the new definition would eventually have been 
diagonsed as having AIDS according to the old definition -- a fact the 
CDC itself admits -- then is it not possible to see the current glut of 
large numbers as a form of artificial inflation designed to impress the 
CDC's clients just at a time when, in fact, the AIDS epidemic may have 
peaked and be on its way down?
    The crucial information is the number of people who would have been 
diagnosed with AIDS according to the new definition had it been in place 
in 1992, or 1990, or even 1985.  These data do not, and can never, exist.
    Even worse, this is not the first time that the definition of AIDS 
has been altered to increase the number of diagnoses.  The definition 
change implemented in 1985 increased the number of AIDS diagnoses about 
2% a year over the 1984 definition; the 1987 changes increased new 
diagnoses 30% to 40% a year; and now the new changes more than double the 
number.  Anyone simple plotting AIDS statistics provided by the CDC year 
by year will be terribly misled by the resulting graph for the simple 
reason that the numbers represent apples one year; apples and oranges 
another; apples, oranges and bananas a few years later; and so forth.
    As James O. Mason, assistant secretary of health and human services, 
told the Los Angeles Times in 1991 when the latest alterations were 
proposed, changing definitions "messes up the baseline for comparison 
from past to future" and "will make the interpretation of trends in 
incidence and characteristics of cases more difficult."  Perhaps that is 
the point.
    Perhaps the CDC does not want anyone to recognize what some 
statisticians and actuaries have been predicting for several years now: 
that AIDS peaked sometime between 1989 and 1992 in the U.S. and is on its 
way down.  Indeed, according to one of the best validated principles of 
epidemiology -- Farr's law -- the epidemic should recede at the same rate 
that it arose.  Think of it: Perhaps those people who were most 
susceptible to AIDS have already contracted the disease and it will 
remain within high risk groups, as the National Research Council report 
predicted last year.  Or even better, maybe safer sex campaigns, clean 
needle exchanges and better health care are having their effects.  Is it 
rally so unthinkable that there is good news on the AIDS front that we 
cannot face it when it appears?
    The upshot of this lesson is a simple one.  The CDC is comparing 
apples with apples and oranges.  That it can get away with such sleights 
of hand only goes to show how really deeply innumeracy runs in this 
society -- innumeracy so pervasive that not even our science reporters, 
our AIDS activists and our researchers seem to notice.  Or is it worse, 
even, than not noticing?  Have we reached the stage in AIDS advocacy that 
we will mislead in order to succeed?

Mr. Root-Bernstein is a professor of physiology at Michigan State 
University.  He is the author of "Rethinking AIDS" (Free Press)
