Figure 1.

Schematic of the Medicare Current Beneficiary Survey (MCBS) study cohort. The rows represent the MCBS cohort (each cohort participates for 4 yrs) and the columns represent the calendar years, broken down by season. The annual “access to care” survey is administered in the fall of each year. The completion date of this survey became the arbitrary start (and, 1 year later, end) of each beneficiary's person-year (PY) of data. Beneficiaries could contribute up to 3 “pre-post” PY of comparison data over their 4 years of participation in the MCBS. We categorized each PY of data according to the patient's Medicare claims for the year. If the person was hospitalized with mechanical ventilation (MV) one or more times in the year, we categorized them as “hospitalized with MV.” If they were hospitalized one or more times in the year without MV (and never had a hospitalization with MV) we categorized them as “hospitalized without MV.” If they were never hospitalized, we categorized them as “not hospitalized.” If they died during the hospitalization, they were not eligible for this study because they were not “survivors” of MV or hospitalization without MV. If they died before the next autumn, they were censored (missing because of death). If they were alive the next autumn, but did not respond to the survey, they were censored (missing because of nonresponse). As expected, this survivor and nonresponse and survivor bias were greater for the MV group. Assuming these decedents and nonresponders were systematically more disabled, our results underestimate the degree of disability among survivors of MV.