Table 3.
Subgroup analysis of SMS reminders effectiveness on improving childhood immunisation timeliness
| Subgroup | No of studies | Sample | Pooled RR | 95% CI | I2 statistic (%) | P value* |
| All studies | 12 | 25 257 | 1.21 | 1.12 to 1.30 | 87.3 | |
| Country’s income status | 0.554 | |||||
| Low-income country | 1 | 523 | 1.22 | 1.01 to 1.47 | – | |
| Lower middle-income country | 10 | 24 014 | 1.20 | 1.10 to 1.30 | 89.5 | |
| Upper middle-income | 1 | 720 | 1.38 | 1.08 to 1.75 | – | |
| Study design | 0.560 | |||||
| Randomised controlled trials | 10 | 13 682 | 1.21 | 1.09 to 1.34 | 87.8 | |
| Non-randomised controlled trials | 2 | 11 575 | 1.25 | 1.19 to 1.32 | 52.4 | |
| Study setting | 0.604 | |||||
| Rural | 4 | 12 728 | 1.20 | 1.09 to 1.31 | 74.9 | |
| Peri-urban (mixed urban and rural) | 2 | 1464 | 1.21 | 1.05 to 1.40 | 45.7 | |
| Urban | 6 | 11 065 | 1.32 | 1.11 to 1.58 | 92.3 | |
| Outcome measured | 0.259 | |||||
| DPT-3 coverage | 7 | 4192 | 1.32 | 1.13 to 1.54 | 91.1 | |
| Overall immunisation coverage | 5 | 21 065 | 1.20 | 1.12 to 1.28 | 72.9 | |
| Time cut-off for timeliness | 0.024 | |||||
| Scheduled vaccination day | 6 | 13 684 | 1.44 | 1.19 to 1.74 | 92.5 | |
| 1–28 days after scheduled day | 6 | 11 573 | 1.14 | 1.08 to 1.22 | 70.5 | |
| Number of SMS reminders sent | 0.040 | |||||
| 1 or 2 SMS reminders | 8 | 20 433 | 1.16 | 1.11 to 1.21 | 59.3 | |
| >2 SMS reminders | 4 | 4824 | 1.91 | 1.18 to 3.07 | 94.9 | |
| Timing of last SMS reminder | ||||||
| Sent 1 or 2 days before scheduled day | 10 | 24 108 | 1.25 | 1.14 to 1.36 | 85.1 | 0.228 |
| Sent on scheduled immunisation day | 2 | 1149 | 0.98 | 0.68 to 1.43 | 88.3 | |
| Risk of bias (quality) of included studies | 0.071 | |||||
| Low risk of bias | 4 | 1871 | 1.76 | 1.14 to 2.70 | 95.2 | |
| Moderate and high risk of bias | 8 | 23 386 | 1.18 | 1.11 to 1.25 | 71.3 |
*χ2 test for subgroup difference.
DPT-3, third dose of diphtheria, pertussis and tetanus; SMS, short message service.