Results of meta-regression of studies of all autism spectrum disorders, univariate analyses (n = 23)
| Covariate* | Categories of covariate (first listed used as baseline) | No. studies | Odds ratio | 95% CI (odds ratio) | p value | τ2 | Variance explained (%) |
|---|---|---|---|---|---|---|---|
| *Too few studies relative to the number of categories in diagnostic criterion 2 (criteria separately) were available to include this covariate in the analysis. | |||||||
| No covariates | 23 | 1.01 | |||||
| Age | Mid-point of age range (continuous variable) | 23 | 0.82 | 0.72 to 0.94 | 0.005 | 0.74 | 27 |
| Decade | 1960s and 1970s | 1 | 1.00 | – | – | 0.43 | 57 |
| 1980s | 6 | 0.29 | 0.07 to 1.19 | 0.09 | |||
| 1990s | 5 | 0.93 | 0.22 to 3.94 | 0.92 | |||
| 2000s | 11 | 1.75 | 0.44 to 6.89 | 0.42 | |||
| Region | N. America | 4 | 1.00 | – | – | 0.77 | 24 |
| Japan | 0 | – | – | – | – | – | |
| Europe | 10 | 1.99 | 0.70 to 5.58 | 0.19 | |||
| Scandinavia | 9 | 0.72 | 0.25 to 2.05 | 0.54 | |||
| Area | Rural/mixed | 17 | 1.00 | – | – | 0.86 | 15 |
| Urban | 6 | 2.44 | 1.02 to 5.81 | 0.05 | |||
| Sample screened | Population based | 14 | 1.00 | – | – | 0.97 | 4 |
| Clinic based | 9 | 0.66 | 0.29 to 1.54 | 0.34 | |||
| Screen method | Routine checks | 3 | 1.00 | – | – | 0.72 | 29 |
| Letter for referrals | 9 | 0.31 | 0.10 to 0.98 | 0.05 | |||
| Questionnaires | 3 | 0.76 | 0.19 to 3.03 | 0.69 | |||
| Records | 8 | 0.93 | 0.30 to 2.97 | 0.91 | |||
| Assessment | Prospective | 14 | 1.00 | – | – | 0.96 | 5 |
| Retrospective | 9 | 1.52 | 0.66 to 3.49 | 0.32 | |||
| Diagnostic criterion 1 | Not ICD-10 or DSM-IV | 9 | 1.00 | – | – | 0.69 | 32 |
| ICD-10 or DSM-IV | 14 | 3.08 | 1.52 to 6.25 | 0.002 | |||