Health Insurance and
Access to Care among
Social Security Disability
Insurance Beneficiaries
during the Medicare
Waiting Period
For most Social Security Disability Insurance (SSDI) beneficiaries, Medicare entitlement begins 24 months after the date of SSDI entitlement. Many may experience poor access to health care during the 24-month waiting period because of a lack of insurance. National Health Interview Survey data for the period 1994–1996 were linked to Social Security and Medicare administrative records to examine health insurance status and access to care during the Medicare waiting period. Twenty-six percent of SSDI beneficiaries reported having no health insurance, with the uninsured reporting many more problems with access to care than insured individuals. Access to health insurance is especially important for people during the waiting period because of their low incomes, poor health, and weak ties to the workforce.
Since 1972, Medicare entitlement has been ex-tended to Social Security Disability Insurance (SSDI) beneficiaries after a 24-month waiting period that begins with the date of SSDI enti-tlement.1 The waiting period for Medicare was mandated by Congress with three primary pur-poses in mind: 1) to limit the costs of the program; 2) to prevent cost shifting from private health in-surance plans to Medicare; and 3) to ensure that Medicare entitlement is extended only to people whose disabilities are severe and long lasting (Committee on Finance 1972). Congress has waived the 24-month waiting period only for SSDI beneficiaries with end-stage renal disease (there is a three-month waiting period) and those with amyotrophic lateral sclerosis (no waiting period). There were more than 1.6 million SSDI awards to disabled beneficiaries in the years 2002–2003 (Social Security Administration
2004); the number of individuals in the Medicare waiting period at any given time cannot be esti-mated with precision from published data, but was probably in the range of 1.4 million to 1.5 million in December 2003.2
There has been concern among policymakers that SSDI beneficiaries may experience poor ac-cess to health care during the waiting period be-cause of difficulty in obtaining health insurance (Riley 2004; Dale and Verdier 2003). Private health insurance provided by an employer or union – the most common source of health insur-ance for the working age population – is unavail-able to many in the waiting period because to qualify for SSDI an individual must be too disabled to work. Continuation of employer-sponsored health insurance coverage is available for some under the Consolidated Omnibus Bud-get Reconciliation Act (COBRA), but tends to
Gerald F. Riley, M.S.P.H., is a senior researcher in the Office of Research, Development, and Information, Centers for Medi-care and Medicaid Services. Address correspondence to Mr. Riley at Office of Research, Development, and Information, Centers for Medicare and Medicaid Services, 7500 Security Blvd., Room C3-20-17, Baltimore, MD 21244. Email: gerald. riley@cms.hhs.gov
be very expensive because the insured individual must pay 102% of the total premium. Nongroup insurance often contains exclusions for pre-existing conditions, provides limited benefits, and tends to be expensive, particularly for people in poor health (Swartz 2002; Hadley and Re-schovsky 2003). Other potential sources of insur-ance are dependent coverage under a spouse’s private insurance plan, Medicaid for individuals with very low incomes, and other public insurers like the Veterans Administration (VA), CHAM-PUS, and state programs. SSDI entitlees are un-likely to be able to purchase directly the health care they need because they tend to have low in-comes (Social Security Administration 2001).
Very little is known about the extent to which SSDI beneficiaries are insured in the waiting period, and about their experiences getting health care. Bye and Riley (1989) estimated that 27% of disabled-worker beneficiaries in the waiting period were uninsured in the early 1980s, based on the Social Security Administration’s New Ben-eficiary Survey. Using the same survey, Muller (1989) found that most beneficiaries with cover-age in the waiting period had private insurance, with 12.2% reporting Medicaid coverage and 11.9% reporting CHAMPUS/VA/military cover-age. Short, Shea, and Powell (2001), using data from the National Institute on Aging Health and Retirement Study, estimated that between 27.4% and 38.9% of new Medicare beneficiaries in 1994 (ages 53 to 63) had been uninsured in the waiting period. Williams et al. (2004) reported serious problems with access to care among 21 SSDI entitlees who were in the waiting period, based on interviews and focus group participation. The purpose of this study is to describe the prevalence of health insurance coverage during the Medicare waiting period and reported access problems by insurance status. Analyses are based on a first-time linkage of the National Health In-terview Survey (NHIS) to Social Security and Medicare administrative records, on an individual basis. Linked data were used for this study, rather than NHIS data alone, because of difficulty in identifying respondents who are in the Medicare waiting period based on survey information. Al-though NHIS respondents are asked about receipt of SSDI benefits and how long they have received them, many respondents may confuse SSDI with Supplementary Security Income (SSI) or other programs, or may not recall accurately the length
of time they have been receiving benefits. More importantly, entitlement to SSDI often is estab-lished retroactively because of delayed filing by the beneficiary or because of the length of time needed for disability claims adjudication, includ-ing the appeals process. Thus, the date of award of SSDI benefits frequently is later than the date of SSDI entitlement (Riley 2004). In such cases, the beginning of the Medicare waiting period is established retroactively. Because NHIS respon-dents are asked about the length of time they have received benefits, and not the length of time they have been entitled, it is not possible in many cases to determine accurately from survey data alone whether an individual was: 1) entitled to SSDI; and 2) in the waiting period at the time of the survey. The linked database therefore provides a unique perspective on the ability of SSDI beneficiaries to obtain access to health care during the waiting period for Medicare. Data and Methods
Data Sources
The NHIS is an annual, cross-sectional house-hold interview survey conducted by the National Center for Health Statistics (NCHS). It collects social, demographic, and health information on the civilian, noninstitutionalized, U.S. resident population. In addition to the health data col-lected in the core survey, each year the survey includes supplements on current health topics, including health insurance and access to care (NCHS 2005).
NHIS data for the period 1994–1998 were linked to Social Security and Medicare adminis-trative records on an individual basis under an in-teragency agreement among NCHS, the Centers for Medicare and Medicaid Services (CMS), the Social Security Administration (SSA), and the Office of the Assistant Secretary for Planning and Evaluation (ASPE). The linkage was under-taken to support various research initiatives of the participating agencies. Social Security num-bers (SSN), name, sex, date of birth, and other variables were used for record linkage and verifi-cation. The SSA matched eligible NHIS records against the Numident file, which contains a record for anyone who has ever been issued a SSN, for the purpose of SSN verification. Extracts of SSA’s current Master Beneficiary Record (MBR) then were obtained for cases with verified SSNs.
The extract contains historical data on entitle-ment to Social Security benefits, including SSDI. An additional, but separate match of NHIS records was made against CMS’ Enrollment Data Base (EDB) to obtain Medicare entitlement information.
The study reported here used data from the pe-riod 1994–1996 because match rates were higher for those years. Among respondents ages 18 to 64 (the age group eligible for SSDI benefits) at the time of their NHIS interview, 21% were ineligi-ble for linkage because of their refusal to pro-vide identifying information, in particular their SSNs (making 79% of records eligible for link-age). Among those eligible, 92% of records were matched successfully to SSA’s Numident file.
After accounting for the NHIS response rate (94%), the effective ‘‘response rate’’ of the NHIS-SSA linked data for people ages 18 to 64 was 68% in the period 1994–1996, comprising 121,227 linked records.
Comparison of Matched and Unmatched Cases Findings from the linked database may not repre-sent the entire NHIS target population if matched cases differ systematically from unmatched cases. Matched cases were defined as NHIS rec-ords that were matched successfully to SSA’s Numident file; unmatched cases consisted of re-spondent refusals and eligible cases for which a matching Numident record could not be found. Among NHIS respondents ages 18 to 64, matches tended to be slightly older, and were less likely to be male, black, and Hispanic (Table 1). They were more likely to be veterans, to have had one or more bed days in the two weeks before their interview, and to report having health in-surance. Missing values for family income and health insurance status were much less common among matches than among nonmatches.
To account for observed differences between matched and unmatched cases, NHIS survey weights for matched cases were adjusted follow-ing a method similar to that used for nonresponse bias in the Medicare Current Beneficiary Survey. The adjustment was made by first estimating lo-gistic regression models for each study year, pre-dicting nonmatches for adults ages 18 to 64. Independent variables were age, sex, black race, Hispanic ethnicity, veteran status, education, in-come, proxy interview status, bed day(s), census region, Metropolitan Statistical Area (MSA) res-idence, number of disease conditions, and health insurance coverage. Within each year, observa-tions were sorted by the predicted probability of a nonmatch and then grouped into cells of 1,000. An adjustment factor then was applied to the NHIS weights for the matched cases in each cell, consisting of the ratio of the sum of the weights for the matched and unmatched cases in the cell to the sum of the weights for the matched cases in that cell. A final adjustment was made to the weights for all matched cases so that the sum of the adjusted weights was iden-tical to the sum of the original NHIS weights. Selected analyses were carried out with both adjusted and unadjusted weights, revealing only Table 1. Characteristics of matched and
unmatched cases: National Health
Interview Survey records for respondents ages 18 to 64, matched to Social Security administrative records, 1994–1996 Characteristic Matched (%)a (N¼ 121,227) Unmatched (%)a (N¼ 46,862) Age ,35 40.9 42.4* 35–49 37.4 37.0 50–64 21.7 20.6* Male 48.5 50.3* Black race 10.9 14.8* Hispanic 8.6 13.6* Family income ,$10,000 8.1 4.9* $10,000–$24,999 21.1 15.2* $25,0001 61.3 46.3* Unknown 9.4 33.6* Veteran 12.6 10.1* Region Northeast 19.2 21.1* Midwest 24.5 22.5* South 35.9 31.4* West 20.4 25.0* Bed day(s) in last 2 weeks 6.1 4.8*
Health insurance coverage
Yes 77.7 63.0*
No 16.4 17.8*
Unknown 5.9 19.2*
Note: Unmatched cases consist of respondent refusals and eligible cases for which a match could not be found. aN values are unweighted; percentages are weighted. *p , .05 for differences between matched and unmatched cases.
small differences in results. This paper reports findings based on adjusted weights.
Methods
NHIS respondents were identified as being in the waiting period at the time of the survey if they were age 18 to 64 and had been entitled to SSDI for 24 or fewer months according to the MBR (N¼ 876 out of 121,227 linked cases). Medicare administrative records were used to confirm that sample members were not yet entitled to Medi-care. Sixty-four individuals who did not respond to the questions about private health insurance or Medicaid coverage (the most common sources of health insurance) were excluded from the study, resulting in a final waiting period sample of 812. Waiting period respondents were considered insured if they answered affirmatively to any question about coverage under private health in-surance (excluding single service or single dis-ease plans), Medicaid, other public assistance, CHAMPUS or VA, other military health care, or the Indian Health Service. Respondents in the waiting period who indicated they had Medi-care coverage also were counted as insured, despite the fact that administrative records indi-cated otherwise, under the assumption that they probably had health insurance but may have confused Medicare with Medicaid or another program. However, some individuals reporting Medicare coverage may have been uninsured but reported having Medicare in anticipation of imminent entitlement. Thirty individuals failed to reply to one or more questions about sources of insurance other than private insurance or Med-icaid; in these cases, the respondent was counted as not having those types of insurance.
The analysis consisted primarily of descriptive statistics. Because the NHIS incorporated differ-ent sample designs in the period 1994–1996, any design-based analyses using pooled data from those years would not yield valid variance esti-mates (NCHS 2005). Therefore, analyses were conducted separately on each year of data; composite estimators were derived by taking a weighted average of year-specific estimators, us-ing sample sizes from each year as the weights. Standard errors of year-specific estimators were calculated using SUDAAN (Shah, Barnwell, and Bieler 1996), and then combined to produce standard errors of the composite estimators.3
Weighted logistic regression models were esti-mated to examine personal characteristics associ-ated with being uninsured during the waiting period. Similar models were used to examine the association of insurance status with various access measures, controlling for several covari-ates. In all cases, regression coefficients and their standard errors were estimated separately for each year and then combined across years in a similar manner to that described earlier. Results
Health Insurance Status
Among respondents who were in the waiting pe-riod, 25.8% reported not having health insurance (Table 2). (For comparison, using unadjusted NHIS weights, the percentage reporting no insur-ance was 24.2% [data not shown in table].) Among the insured, 63.4% reported having pri-vate insurance and 28.9% reported having Med-icaid. Medicare coverage was reported by 7.5% of the insured, which may indicate misreport-ing of Medicaid or another type of insurance. Each of the other sources of coverage was Table 2. Health insurance status of Social Security Disability Insurance beneficiaries in the 24-month waiting period for Medicare, 1994–1996
Percent (weighted) Standard error (%) Insured status (N¼ 812) 100.0 Insureda 74.2 1.7 Uninsured 25.8 1.7
Type of health insurance reported among insured (N¼ 614)b 100.0 Private 63.4 2.2 Medicaid 28.9 2.0 CHAMPUS/Dept. of Veterans Affairs 4.0 .9
Other military health care 5.2 .9
Indian Health Service .4 .3
Other public assistance 3.2 .8
Medicare 7.5 1.1
Source: National Health Interview Survey linked to the Social Security Master Beneficiary Record and Medicare entitlement records, 1994–1996.
Note: Excludes individuals for whom health insurance status was unknown.
a
Includes individuals who reported having Medicare. bPercents add to more than 100 because some respondents reported having more than one type of insurance.
reported by less than 6% of respondents. Per-centages add to more than 100% because re-spondents could report having more than one source of insurance.
Among those reporting private insurance cov-erage, 89% reported that an employer or union was the source of that coverage. Among those with an employer or union as the source of cover-age, 61% reported that the plan was in the respond-ent’s name (data not in tables). The latter group presumably includes individuals who obtained insurance coverage through COBRA, but they could not be identified separately from the data.
The most common reason given for lacking health insurance was that it was too expensive or unaffordable (78%) (Table 3). This is consis-tent with the fact that 27% of respondents in the waiting period reported income that was be-low the poverty threshold, excluding those for whom poverty status was unknown (data not in table). Twenty-two percent of uninsured individ-uals reported job loss/unemployment as a reason for being uninsured. Seventeen percent gave poor health, illness, or age as a reason – all of which could contribute to high premiums in the indi-vidual market or be the reason people were denied coverage. Percentages in Table 3 add to more than 100% because respondents could re-port more than one reason for being uninsured.
Logistic regression analysis indicated that the most important characteristic associated with
lack of insurance during the waiting period was income below the poverty threshold (odds ratio [OR]¼ 1.75, 95% CI ¼ [1.18, 2.61]) (see Table 4). Men were significantly more likely to be un-insured than women (OR¼ 1.67) and black peo-ple were more likely to be uninsured than respondents of other races (OR¼ 1.64). Veterans were significantly less likely to be uninsured (OR ¼ .47), presumably because of the availability of VA health benefits, which are counted as insur-ance. Among the most common reasons for dis-ability, diseases of the musculoskeletal system were associated with a higher rate of uninsurance (OR¼ 1.71). Separate models were estimated in-corporating variables for marital status and whether the respondent was in the first 12 months of the waiting period; neither of these variables Table 3. Reasons reported for not having
health insurance among uninsured Social Security Disability Insurance beneficiaries in the 24-month waiting period for Medicare, 1994–1996
Percent (weighted)
Standard error (%) Reason for not having
health insurance (N¼ 183)
Too expensive/can’t afford 77.7 3.4
Job loss 21.5 3.3
Can’t obtain because of
poor health, illness, or age 17.0 3.0
Benefits ran out 8.4 2.2
Other 24.6 3.6
Source: National Health Interview Survey linked to the Social Security Master Beneficiary Record and Medicare entitlement records, 1994–1996.
Note: Table excludes 15 individuals who did not report a reason for being uninsured. Among those reporting reasons, more than one reason could be reported.
Table 4. Factors associated with lack of health insurance among Social Security Disability Insurance beneficiaries who were in the 24-month waiting period for Medicare, 1994–1996 Beneficiary characteristics Odds ratio 95% confidence interval Intercept .11 (.05, .22)* Age ,55 1.50 (1.00, 2.25) Male 1.67 (1.10, 2.52)* Black race 1.64 (1.04, 2.58)* Veteran .47 (.26, .86)*
Below poverty threshold 1.75 (1.18, 2.61)* Region
Northeast 1.14 (.58. 2.25)
Midwest .84 (.42, 1.70)
South 1.72 (.99. 2.99)
West 1.00 —
Reason for disability
Mental disorders 1.20 (.69, 2.10) Diseases of musculoskeletal system 1.71 (1.06, 2.75)* Diseases of circulatory system .75 (.40, 1.43) Neoplasms 1.40 (.62, 3.15) Other 1.00 — N¼ 812
Source: National Health Interview Survey linked to the Social Security Master Beneficiary Record and Medicare entitlement records, 1994–1996.
Notes: Findings were obtained from a weighted logistic regression model with insurance status (1 ¼ uninsured, 0 ¼ insured) as the dependent variable. Model excludes individuals for whom insurance status was unknown.
was significantly associated with insurance status (results not shown).
Access Measures
Respondents in the waiting period who lacked health insurance frequently reported problems with access to care (Table 5). Twenty-two percent reported they needed care but were unable to get it, and 46.5% delayed seeking care because of cost, compared to 4.7%, and 13.2%, respectively, of in-sured individuals. The uninin-sured were much more likely to report they needed prescription medicine and could not get it (28.9%, compared to 4.8% for the insured). They also were much more likely to report problems getting dental care, eyeglasses, and mental health care. The differences between the insured and uninsured remained highly signif-icant after controlling for demographic factors, poverty status, and reason for disability.
Discussion
The waiting period for Medicare entitlement is a vulnerable time for the SSDI population because of its members’ poor health and low incomes. Over a quarter of those in the waiting period re-ported they had no health insurance at the time of their NHIS interview in the mid-1990s. If that percentage did not change substantially, there were approximately 375,000 individuals unin-sured in the waiting period nationally at the end of 2003.4At the time of this study, the percentage
of individuals in the waiting period without health insurance was higher than that among the nonelderly adult population (Holahan and Pohl 2002). Access problems also were reported more frequently by uninsured individuals in the waiting period than by all uninsured adults ages 18 to 64 (Bloom et al. 1997).
Coverage for the Uninsured
It is difficult to design policies that are targeted specifically to the uninsured in the waiting period because entitlement to SSDI often is established retroactively. Because of retroactive entitlement, many individuals are not identifiable as SSDI en-titlees early in the waiting period, and are un-aware the waiting period has begun until after the fact. Policies to assist the uninsured in the waiting period may need to target broader groups of people with disabilities and chronic illness.
The primary reason for lacking insurance dur-ing the waitdur-ing period was affordability, suggest-ing financial subsidies would be one method of increasing the number of insured. Several pro-posals have involved the use of tax credits or other mechanisms to make insurance in the non-group market more affordable for low-income in-dividuals (McClellan and Baicker 2002; Davis and Schoen 2003; Glied 2001). Financial assis-tance also could be provided to individuals in the waiting period by subsidizing premiums for COBRA coverage (Ellwood and Burwell 1990). Table 5. Access measures for Social Security Disability Insurance beneficiaries who were in the 24-month waiting period for Medicare, by health insurance status, 1994–1996 Access measure Insured (%)a (N¼ 614) Uninsured (%)a (N¼ 198) Odds ratio for uninsuredb 95% confidence interval
Needed care but not able to get it 4.7 22.0* 5.27 (3.02, 9.19)**
Delayed seeking medical care because of cost 13.2 46.5* 6.48 (4.29, 9.79)**
Needed prescription medicine but could not get it 4.8 28.9* 9.20 (5.30, 15.95)**
Needed mental health care but could not get it 2.2 9.2* 5.12 (2.14, 12.26)**
Needed dental care but could not get it 11.5 31.3* 3.17 (2.05, 4.90)**
Needed eyeglasses but could not get them 8.7 20.2* 2.45 (1.47, 4.06)**
Source: National Health Interview Survey linked to the Social Security Master Beneficiary Record and Medicare entitlement records, 1994–1996.
Note: Excludes individuals for whom health insurance status was unknown. aPercents are weighted.
b
Odds ratios derived from weighted logistic regression models with access measures as the dependent variables. Odds ratios adjusted for age, sex, black race, poverty, and reason for disability.
*p , .05 for comparison of insured and uninsured. ** Confidence interval excludes 1.00.
The fact that 22% cited job loss or unemployment as a reason for being uninsured suggests that COBRA-related subsidies might have a significant impact. Under current law, SSDI entitlees can receive COBRA coverage for up to 29 months, a length of time designed to span the five-month waiting period for SSDI entitlement and the 24-month waiting period for Medicare entitlement.
As noted earlier, 17% of the uninsured re-ported they had no insurance because of poor health, illness, or age; many of these individuals may be uninsurable in the private market, and would not benefit from tax credits for health in-surance premiums alone. Federal reinin-surance and the expansion of state high-risk pools have been proposed as ways of expanding insurance options for people in poor health who might not otherwise have access to insurance (Swartz 2006, 2002; Hadley and Reschovsky 2003). Reg-ulatory changes in the nongroup insurance mar-ket also could broaden access to insurance. An expanded Medicaid program, possibly including a buy-in arrangement, would be another potential mechanism for extending health insurance cover-age to low-income individuals with disabilities, including those in the waiting period (Etheredge and Moore 2003; Weil 2001). Medicaid buy-in programs currently exist for some working dis-abled individuals through state programs autho-rized under the Balanced Budget Act of 1997 (BBA) and the Ticket to Work and Work Incen-tives Improvement Act of 1999 (TWWIIA) (Ireys, White, and Thornton 2003).
Eliminating the Waiting Period
There has been interest among policymakers in eliminating the waiting period by making Medi-care entitlement effective at the same time as SSDI entitlement. Based on linked SSA-Medicare ad-ministrative records, Riley (2004) estimated it would have cost Medicare $5.3 billion (in 2000 dollars) to eliminate the waiting period for dis-abled workers younger than age 62 who were newly entitled to SSDI in 1995. Dale and Verdier (2003) estimated it would have cost Medicare $8.7 billion to eliminate the waiting period for all SSDI beneficiaries in 2002. Both studies as-sumed Medicare would be the primary payer in most cases.
The elimination of the waiting period also would result in significant cost shifting among
payers. For example, some of the costs to Medi-care of eliminating the waiting period would be offset by savings in the Medicaid program, as-suming Medicare became primary payer for in-dividuals also entitled to Medicaid (Dale and Verdier 2003). Elimination of the waiting period also could lead to an increase in SSDI applica-tions which might affect the costs of both the SSDI and Medicare programs (Gruber and Kubik 2002). It should be noted that making Medicare entitlement coincide with SSDI entitlement might involve some administrative complexity because of the retroactivity of many SSDI awards. That is, Medicare entitlement frequently would be estab-lished retroactively, and claims for some services would have to be submitted and paid after the fact.
There are less costly alternatives to complete elimination of the Medicare waiting period. For example, SSDI beneficiaries could be allowed to buy in to Medicare during the waiting period, with appropriate subsidies. A buy-in policy would minimize the displacement of private coverage by Medicare, alleviating a policy concern that led to the establishment of the waiting period. The wait-ing period also could be reduced to one year, or could be eliminated only for certain subgroups of beneficiaries. Costs also could be reduced by making Medicare a secondary insurer whenever other types of insurance were available.
Limitations
This study is based on data from the mid-1990s. Trends in the availability of insurance may have changed the percentage of SSDI beneficiaries who are uninsured in the waiting period. For ex-ample, the percentage of adults under age 65 who lack insurance has increased in recent years, es-pecially among those with low incomes (Holahan and Cook 2005). At the same time, legislative developments such as the BBA and TWWIIA, which extend Medicaid coverage to certain work-ing individuals with disabilities, may have re-duced the levels of uninsurance in the waiting period. Second, information on health insurance and other factors is based on self-reports, which are subject to measurement error. Third, the level of Medicaid coverage in the waiting peri-od (28.9% of insured individuals) may be under-reported because of the time required to process disability applications under SSI. The disability
determination process sometimes results in eligi-bility for SSI and Medicaid benefits being
estab-lished retroactively, similar to SSDI.
Consequently, some respondents in the waiting period may have been eligible for Medicaid ben-efits at the time of the survey, but were unaware of that fact because their eligibility had not yet been determined. Medicaid eligibility also tends to be underreported in surveys, but underreport-ing may not have a strong impact on estimates of uninsurance (Call et al. 2001/2002). Lastly, this study is limited to the noninstitutionalized population.
Conclusion
Access to health insurance and health care is es-pecially important for people in the Medicare waiting period because of their low incomes, poor health, and weak ties to the workforce. Until now, it has been difficult to evaluate access prob-lems due to the lack of information in standard data sets about individuals in the waiting period. The linkage of NHIS and administrative data provides a unique contribution to our under-standing of the experiences of SSDI beneficiaries before their Medicare entitlement begins.
Notes
The author wishes to thank the following individuals for their efforts in creating the linked database used for this article: Christine Cox, Sandra Rothwell, Cordell Gold-en, Bert Kestenbaum, Joel Packman, Charles Herbold-sheimer, and John Drabek. Kimberly Lochner’s assistance with statistical methodology also is much ap-preciated. The author also thanks Barry Bye, Bert Kestenbaum, Brigid Goody, and James Lubitz for their helpful comments on earlier drafts of the paper. The statements contained in this article are solely those of the author and do not necessarily reflect the views or policies of the Centers for Medicare and Medicaid Services.
1 In addition to the Medicare waiting period, there is a five-month waiting period between the onset of disability and entitlement to SSDI benefits. 2 The number of individuals in the waiting period at
a given point in time depends on the number of peri-ods of SSDI entitlement that began in the prior two years. This is difficult to estimate accurately because data on new SSDI entitlements are published by dates of awards. Because many dates of entitlement are
es-tablished retroactively at the time of award, the num-ber of SSDI awards during the period 2002–2003 yields only a rough approximation of the number of new periods of SSDI entitlement begun in those years. An estimate of the number of individuals still in the waiting period at the end of 2003 can be ap-proximated by the number of new SSDI awards dur-ing 2002–2003, reduced by the estimated numbers of deaths, recoveries, and repeat entitlements in which the waiting period was satisfied previously (Riley 2004). Given that there were about 1.6 million SSDI awards during 2002–2003 (Social Security Adminis-tration 2004), the number of people in the Medicare waiting period at the end of 2003 was probably in the range of 1.4 million to 1.5 million.
3 LetX1–X3represent year-specific estimators from the period 1994–1996 andV1–V3represent their estimat-ed variances. Letn1–n3 represent sample sizes from those years. If p1¼n1/(n1þn2þn3); p2¼n2/(n1þn2þn3); p3¼n3/(n1þn2þn3), then the composite estimator is Xc¼p1*X1þp2*X2þp3*X3 and its estimated standard error is s.e.(Xc)¼square root(p1
2 *V1þp2 2 *V2þp3 2 *V3). 4 Based on an estimated 1.4 million to 1.5 million
people in the waiting period at that time.
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