Quality assessment of included studies by the modified Newcastle-Ottawa Scale (NOS)
| Author (year) | Adequate definition of cases using insulin | Representativeness of cases using insulin | Selection of the non-insulin users | Ascertainment of insulin use | Depression was not present before insulin initiation | Control of confounding factors | Assessment of depression | Report response rates or follow-up data | Total score |
| Katon et al 21 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 8 |
| Bell et al 20 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 7 |
| Noh et al 17 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 0 | 6 |
| Hermanns et al 40 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 0 | 6 |
| Pawaskar et al 31 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 7 |
| Li et al 18 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 0 | 6 |
| Ali et al 33 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 7 |
| Raval et al 36 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 7 |
| Zuberi et al 42 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 7 |
| Stanković et al 41 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 0 | 6 |
| Lynch et al 43 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 7 |
| Osme et al 44 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 0 | 6 |
| Trento et al 45 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 0 | 6 |
| Roy et al 37 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 8 |
| Joseph et al 46 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 0 | 6 |
| Hayashino et al 47 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 0 | 6 |
| Gorska-Ciebiada et al 34 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 6 |
| Sweileh et al 48 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 7 |
| YY Zhang et al 52 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 7 |
| Rodriguez Calvin et al 51 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 7 |
| Camara et al 35 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 0 | 6 |
| Sun et al 39 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 7 |
| WJ Zhang et al 32 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 8 |
| Luca et al 50 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 0 | 6 |
| Kikuchi et al 49 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 0 | 6 |
| Jacob et al 38 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 0 | 6 |
| Cols-Sagarra et al 53 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 0 | 6 |
| Habtewold et al 54 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 7 |