In each model, we included a variable denoting year of NDATSS to control for time trends in the dose patterns in OAT programs.
Unfortunately, the NDATSS did not elicit the attitudes of directors toward methadone and other substance abuse treatment practices.
Unfortunately, the NDATSS also did not consistently measure the racial/ethnic composition of the staff of an OAT program.
Unfortunately, these factors were not systematically documented by the NDATSS.
When a given OTP displayed missing values for these variables, we imputed values by calculating predicted values using multiple regression analysis based on dummy variables for NDATSS survey wave and the observed values of these variables within the same OTP program in other waves, We compared results obtained with imputed and nonimputed data and found that imputation had no substantive impact on our point estimates but increased our sample size in pooled regression analysis from 339 to 370 programs.
Comparisons with client-level surveys indicate high validity of NDATSS data; therefore, this limitation should not bias the results.
More specifically, each wave of the NDATSS involved several steps.
We have conducted several studies of NDATSS data reliability and validity.
Further, to evaluate the validity of NDATSS methadone dose data, we compared them with data obtained from two other national studies, DSRS (described above), and a study by Kleber et al.
The NDATSS is a telephone survey of the administrative director and clinical supervisor at each OSAT unit.
The nature of the data from the NDATSS suggests caution in generalizing study results.
The 1990 NDATSS data were compared with the Drug Services Research Study (DSRS), an independent national study of treatment units and clients conducted in 1990 (Batten et al.