Initially severity was limited to BDI-II scores of 14 28 and the minimisation strata were scores of 14 – 19 (mild) and 20 28 (moderate) [ 16].
The outcome distributions in derivation 33 and validation studies of ABCD rule, overall and according to three strata of stroke risk (scores 0 3, 4 5, and 6 7), are presented in Figure A1.4 and Table A1.1 (Supplementary materials).
However, because of substantial heterogeneity of risk estimates across propensity score strata (likely because the propensity score was highly discriminative (that is, a high C statistic) given substantial differences in characteristics between TNF-α inhibitor users and non-users), which violates the basic assumptions of this approach, it was abandoned.
To check the prognostic value of studied variables on follow-up BMC, we fitted multiple regression models, both without and after adjustment for baseline values of age, body mass index (BMI), erythrocyte sedimentation rate (ESR), smoking, QCT derived BMC stratum, radiologic score and duration of disease prior to baseline visit.
In the current analysis, we defined 5 propensity score strata based on the quintiles of the propensity scores in the overall sample.
Using non-linear regression, we fitted a function corresponding to the mathematical description of PPV by specificity, sensitivity, and individual odds (represented by the score) to observed PPV in eight strata with different scores.
Using the STATA 10.0 "atts" command, the full range of sample members' propensity scores is divided into propensity score strata, or blocks, each of which includes treatment and control cases with the same or nearly the same propensities for receiving the treatment.
Log-rank test comparing each strata of the score with each other found that the survival probability for score = 3 and score = 4 was different of each other strata (Additional file 5: Table S3; Additional file 6: Fig. S3).
A trend towards lower scores in lower socioeconomic stratum was observed (Primary index score-2.9, 3.7 and 4.0 in lower, middle and higher strata; Secondary Index Score-2.6, 3.2 and 3.0 in lower, middle and higher strata).
The population is divided into subgroups based on estimated propensity score, and the exposed and unexposed subjects are compared within strata of propensity score.
