Program-levelPrimary medical care availability in the treatment program, the primary explanatory variable, was determined from questionnaires completed by program administrators. This variable was dummy-coded to indicate whether (1) on-site care was available through the program, (2) only off-site care was available through the program, or (3) no primary medical care was available through the program (the referent category). We validated these administrator-level measures with patient reports of whether and where they received primary medical services during treatment.
Treatment modality, an indicator of the program's treatment philosophy and patient selection,12 was also determined from the administrative questionnaires. Dummy variables indicated whether a patient attended a methadone, short-term residential, or long-term program. Outpatient nonmethadone program was the referent modality. Because the program-level methadone modality was highly correlated with patient-level methadone status at 12-month follow-up (see below), the program-level indicator variable for methadone modality was dropped from the multivariable models.
Geographic region is the area of the United States in which the program was located: Northeast, South, Midwest, or West. The western region was the referent.
Patient-levelAddiction severity score, one of the primary outcomes, was a multidimensional composite measure similar to the validated Addiction Severity Index.1,13 Because NTIES did not include a validated multidimensional instrument to measure addiction severity, we developed this composite score to provide a comprehensive measure of the totality of problems from which the substance-abusing patient suffered. In addition to the domains of alcohol and drug use, employment, illegal activities, family and other social support, medical conditions, and psychiatric status included in the Addiction Severity Index, our addiction severity score incorporated legal supervision status and housing information. Reports of behavior and subjective ratings were combined and standardized into scale values that could range from 0 to 100 in each domain. Cronbach α tests of internal consistency for these domains ranged from 0.61 to 0.66 at follow-up and 0.31 to 0.45 at intake.
The dependent variable, addiction severity score at follow-up, was developed with the recognition that a comprehensive measure might lack internal reliability. This dependent variable was the sum of the component domain scales to a maximum value of 900. The resultant addiction severity score had Cronbach α coefficients of 0.66 at follow-up and 0.41 at intake, which reflect the heterogeneity of its components.14 Addiction severity score at intake ranged from 53 to 677, and addiction severity score at follow-up ranged from 0 to 653, with higher score indicating greater impairment. We also developed a version of this score with components related to medical severity excluded so that we could include the remaining domains of addiction severity as an explanatory variable in the model predicting medical severity score at 12-month follow-up.
Medical severity score, the other primary outcome, is a composite measure of perceived health, functional limitations, and comorbid physical conditions. Because NTIES did not include a standard instrument to measure health status and illness burden, we derived this composite score from a principal component analysis of 9 survey items. The 9 items are: (1) general health (“In general, would you say your health is excellent, good, fair or poor?”); (2) health limits on work (“Right now, how much does your health limit the kind of work you can do? Would you say not at all, somewhat, or very much?”); and 7 areas of comorbid physical conditions: “Have you had any of problems with …” (1) “your sight, that is, you've had difficulty seeing even with glasses or contact lenses?”; (2) “your hearing, that is, you've had difficulty hearing even with a hearing aid?”; (3) “a serious heart or blood condition, including high blood pressure, or anemia?”; (4) “another serious internal condition, such as stomach ulcers, sugar diabetes, or kidney or liver or female problems?”; (5) “a serious bone or muscle condition, such as being paralyzed, bad arthritis, limping, or bursitis?”; (6) “a serious nerve condition, such as convulsions, epilepsy, or migraine headaches? Please do not include any mental health problems”; and (7) “Other than anything you've told me about, since (date 30 days ago), has any other health problem caused you pain, limited your activities, or caused you any other problems?”
The medical severity composite score used the factor-based method. The result was validated using a separate factor-score–based approach, which revealed that the modeling results were stable.15 The medical severity score had a Cronbach α of 0.71 at follow-up and 0.72 at intake, which indicates sufficient internal consistency.14 Both intake and follow-up medical severity scores ranged from 2 to 14, with higher score indicating greater impairment.
Depressive symptom status was defined on the basis of 4 items in the NTIES intake patient surveys: (1) “Have you had a period of 2 weeks or longer when you have felt either very sad or depressed?”; (2) “Have you had a period of 2 weeks or more when you lost interest and pleasure in things you care about?”; (3) “Have you thought seriously about committing suicide?”; and (4) “Have you tried to commit suicide?” Questions (3) and (4) were combined into a dummy variable to indicate whether a patient had suicidal thoughts or behavior. A second dummy variable, created from questions (1) and (2), indicates whether a patient reported depressive symptoms only.
Drug injection in the past 12 months, a sign of more advanced addiction and possibly of more need for medical care, is a binary variable that indicates whether the patient had “used a needle, even one time, to inject drugs to get high or for other nonmedical effects” in the past 12 months (0 = no, 1 = yes). The patient could have injected him- or herself, or been injected by someone else.
Treatment duration, the number of days of treatment divided by 30, is a continuous variable measuring the approximate number of months the respondent spent in drug treatment. This variable was included because a longer duration of treatment might provide a greater opportunity to access needed services. Treatment duration was derived from a combination of information from the treatment discharge questionnaire and patient record abstraction. For some respondents, primarily methadone maintenance patients, treatment duration is a measure of the duration of treatment up to administration of the 12-month follow-up. Treatment duration ranged from 0.033 to 24.4 months, and varied greatly by modality.
Methadone status at 12-month follow-up indicates whether the patient remained in methadone maintenance, had completed withdrawal from methadone treatment (i.e., detoxification), or received treatment other than methadone (the referent group). This dummy-coded variable is included because a need for methadone, particularly for methadone maintenance, might indicate patients with greater severity of addictive problems, as well as those for whom the program had greater opportunity to facilitate delivery of needed services.
Age, race/ethnicity, education, and marital status, taken from the intake questionnaire were included as demographic characteristics, in the form shown in Table 1.
Table 1. Program- and Patient-level Characteristics by Primary Medical Care Availability.
| || ||Primary Medical Care Availability*|
|Variables||Overall||On-site Care Available||Only Off-site Care Available||No Primary Care Available|
| Total number of programs||52||20||13||19|
| Treatment modality, †|
| Short-term residential||6||6||0||0|
| Long-term residential||15||7||5||3|
| Nonmethadone outpatient||25||4||8||13|
| Geographic region, n‡|
| Total number of patients||2,878||1,387||493||998|
| Addiction severity at intake, mean (SE)||349 (5.8)||358 (8.9)||320 (11.8)‡||358 (9.0)|
| Addiction severity at 12-mo follow-up, mean (SE)||166 (5.8)||162 (9.1)||151 (12.2)||178 (9.3)|
| Medical severity at intake, mean (SE)||4.6 (0.1)||4.7 (0.2)||4.0 (0.2)†||4.9 (0.2)|
| Medical severity at 12-mo follow-up, mean (SE)||4.3 (0.1)||4.3 (0.2)||3.9 (0.2)||4.5 (0.2)|
| Depressive symptoms, n (%)|
| Suicidal thoughts/behavior||289 (10.0)||102 (7.4)†||46 (9.3)||141 (14.1)|
| Depressive symptoms only||806 (28.1)||349 (25.1)||149 (30.2)||308 (30.9)|
| No depressive symptoms||1,783 (62.0)||936 (67.5)||298 (60.5)||549 (55.0)|
| Drug injection in the past 12 months, n (%)|
| Yes||644 (22.4)||375 (27.0)||56 (11.4)||213 (21.3)|
| No||2,234 (77.6)||1,012 (73.0)||437 (88.6)||785 (78.7)|
| Treatment duration, mean n mo (SE)||5.5 (0.5)||5.9 (0.8)||4.8 (1.0)||5.6 (0.8)|
| Methadone status at 12-mo follow-up, n (%)|
| Methadone maintenance||195 (6.8)||123 (8.9)||0§||72 (7.2)|
| Withdrawn from methadone||174 (6.1)||83 (6.0)||0§||91 (9.1)|
| Treatment other than methadone||2,509 (87.2)||1,181 (85.2)||493 (100)||835 (83.7)|
| Ethnicity/race, n (%)|
| Non-Hispanic black||1,558 (54.1)||816 (58.8)||224 (45.4)||518 (51.9)|
| Non-Hispanic white||843 (29.3)||390 (28.1)||218 (44.2)†||235 (23.6)|
| Other||477 (16.6)||181 (13.1)||51 (10.3)||245 (24.6)|
| Age in years, n (%)|
| ≤20||295 (10.3)||69 (5.0)||142 (28.8)||84 (8.4)|
| 21 to 30||941 (32.7)||523 (37.7)||145 (29.4)||273 (27.4)|
| 31 to 40||1,145 (39.8)||556 (40.1)‡||143 (29.0)§||446 (44.7)|
| ≥41||497 (17.3)||239 (17.2)||63 (12.8)‡||195 (19.5)|
| Marital status, n (%)|
| Currently married at intake||603 (21.0)||323 (23.3)||73 (14.9)||207 (20.8)|
| Ever married||469 (16.3)||234 (16.9)||59 (12.0)||176 (17.7)|
| Single||1,800 (62.7)||828 (59.8)||359 (73.1)||613 (61.6)|
| Educational attainment, n (%)|
| At least high school graduate||1,385 (48.1)||730 (52.6)||208 (42.2)||447 (44.8)|
| Did not graduate from high school||1,493 (51.9)||657 (47.4)||285 (57.8)||551 (55.2)|