Medicaid Managed Care - U.S. Senate Special Committee on Aging

creased since MOS data collection ended
in the early 1990s, high-risk patient
groups may be at an even greater risk
today. If information systems for monitoring
and improving the quality of care
ae better now and if health promotion
and disease prevention initiatives are
more successful in HMOs, MOS results
may not apply to current health care.
The MOS was not a randomized trial;
such trials are rare in health care policy
research." Although quasi-experimental
methods' achieved equivalent average
baseline health status scores for
nearly all pairwise comparisons between
FFS and HMO systems of care, unmeasured
risk factors could have bhised es-
timates of differences mn outcomes. Further,
differences in outcomes that
occurred 'on the watch" of the FFS and
HMO systems are not necessarily their
csponsibility. Structural and process
differences in care beyond their control,
such as arrangements for home health
and long-term care, may account in part
for MOS findings.
The MOS monitored outcomes in only
3 large urban cities; results should not
be generalized to HMO or FFS plans in
other cities or rural areas. Although the
MOS reprsented 5 chronic conditions
and many patients had comorbid conditions
such as angina, back pain/sciatica,
lung disease, and osteoarthritis, these
patients do not necessarily represent
other conditions or results of care provided
by other medical specialties. Al
patients had a regular source of care.
All patients were being actively treated
when the MOS began, and only three
fourths who agreed to participate were
followed up longitudinally.
Two potential sources of bias in estimates
of health outcomes-plan switching
and loss to follow-up-were systematically
studied. Patient loss to followup
is an unlikely source of bias in
comparisons of outcomes between systems
because adjusted physical health
scores at baseline did not differ between
FFS and HMO cohorts followed within
the total sample or for elderly or poverty
subgroups (Tables 3 through 5).
Further, all study participants were followed
up through 1993 to determine their
survival.' Seven years after baseline,
those included and not included in this
4-year analysis were equally likely to
have survived (MOS unpublished data).
Two of 10 HMO patients switched to
an FFS plan by the end of the 4-year
follow-up. Comparisons between systems
could have been biased had these
rates differed within elderly or poverty
subgroups or had switchers experienced
different outcomes than nonswitchers.
However, rates of switching did not differ
for elderly or poverty subgroups,
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and system differences in physical and
mental health outcomes were indistinguishable
for those who stayed in the
same system, in comparison with those
who switched (MOS unpublished data).
Thus, it is unlikely that conclusions about
system differences in outcomes were biased
by switching. Because more than
two thirds of patients who switched systems
during the follow-up period had
been in their system at least 6 years
before switching, we adhered to the logic
of intent to treat and analyzed patients
according to the systems from which
they were sampled. The finding that
MOS patients were significantly more
likely to switch from an HMO than to an
HMO (20% vs i5%; 2 =72, P