In their article on stillbirth trends, Ananth et al. note that, not
only are goals for reducing health disparities far from being met,
disparities in some health indicators have widened.1 Their own study
showed that between 1981 and 2000 white still birth rates declined by 46%,
while black stillbirth rates declined by only 33%, with the result that
the ratio of the black stillbirth rate to the white stillbirth rate rose
from 1.7 to 2.1. Thus, stillbirths is another area where the racial
disparity, measured in relative stillbirth rates, is widening. In another
recent study in this journal, Pickett et al. found racial disparities in
sudden infant death syndrome (SIDS), measured in terms of relative SIDS
rates, also to be widening.2
Yet any appraisal of trends in health disparities based on lower
rates of mortality declines for blacks, or the corresponding increasing
relative difference in mortality rates in times of declining mortality,
must take into account the following statistical tendency: When two
groups differ in their susceptibility to an outcome, the rarer the
outcome, the greater the disparity in experiencing it and the smaller the
disparity in avoiding it. Such tendency is evident in any data set that
allows one to examine the relative situation of two groups at different
points on a continuum.3,4,5. A corollary to that tendency is that when an
outcome declines, the less susceptible group has a greater proportionate
reduction in rates of experiencing the outcome than the more susceptible
group (while the more susceptible group has a greater proportionate
increase in rates of avoiding the outcome).4,5.
Fortunately, most adverse health outcome are declining. But the
accompanying increases in relative differences of experiencing the outcome
are regarded as reflecting increasing health disparities in a meaningful
sense, without consideration of whether the increase in relative
differences is greater or less than would be expected to occur solely as a
consequence of a decline in the prevalence of the outcome. And the
declining disparity in rates of avoiding the outcome – as in fact occurred
with respect to black and white rates of avoiding stillbirth between 1981
and 2000 – is usually overlooked.
But not all adverse outcomes are declining. Ananth et al. also note
that stillbirth rates among women 35 years or older have been increasing,
and that the rates have increased more for whites than for blacks. That
may seem like a narrowing of the black-white gap for that age group. But
the change must be appraised with an appreciation that, just as declining
outcomes tends to decline more among the less susceptible group,
increasing outcomes tend to increase more among less susceptible
groups.4,5. So whether that gap has narrowed in any meaningful sense is
an open question.
Given these statistical tendencies, there is a question whether we
can very often determine whether health disparities have increased (or
decreased) in a meaningful sense.3. But it clearly is impossible to do so
without recognizing these tendencies.
References:
1. Ananth CV, Shiliang L, Kinzler WL, Kramer MS. Stillbirths in the
United States, 1981-2000: An Age, Period and Cohort Analysis/ Am J.
Public Health. 2005;95:2213-2217.
2. Pickett KE, Luo Y, Lauderdale DS. Widening social inequalities
in risk for sudden infant death syndrome. Am J Public Health. 2005;95:97-
81.
3. Scanlan JP. Can we actually measure health disparities? Chance.
2006:19(_): ____ (in press).
4. Scanlan JP. Race and mortality. Society. 2000;37:19-35.
5. Scanlan JP. Divining difference. Chance. 1994;7:38-39,481.