Table 2.
Quality assessment of individual study.
| Study | Allocation sequence generation | Allocation concealment | Blinding | Lost to follow-up | Calculation of sample size | Statistical analysis | Level of quality | ITT‡ analysis |
|---|---|---|---|---|---|---|---|---|
| Leff 1998 | B | A | A | 1 | Yes | ANOVA † Fisher's exact test |
B | Yes |
| Knorr 1998 | A | A | A | 2 | Yes | ANOVA † Shapiro-Wilks test Cochran-Mantel-Haenszel test |
A | Yes |
| Noonan 1998 | A | A | A | 0 | Yes | ANOVA † Fisher's exact Cochran-Mantel-Haenszel test Tukey's modified linear trend test (stepwise trend test) |
A | Yes |
| Reiss 1998 | A | A | A | 11 | Yes | ANOVA † Cochran-Mantel-Haenszel test |
A | Yes |
| Malmstrom 1999 | A | A | A | 13 | Yes | ANOVA † Dunnet–Tamhane approach, Shapiro–Wilk statistic, Levene test |
A | No |
| Meltzer 2000-1 | A | A | A | 4 | Yes | ANOVA † Fisher exact test Cochran-Mantel-Haenszel test; |
A | No |
| Meltzer 2000-2 | A | A | A | 4 | Yes | ANOVA † Fisher exact test Cochran-Mantel-Haenszel test; |
A | No |
| Nayak 2002-1 | A | A | A | 3 | Yes | ANOVA † Wilcoxon rank sum test |
A | Yes |
| Nayak 2002-2 | A | A | A | 3 | Yes | ANOVA † Wilcoxon rank sum test |
A | Yes |
| Baumgartner 2003 | A | A | A | NA | Yes | ANOVA † | A | Yes |
| Baena-Cagnani 2003 | A | A | A | 0 | Yes | ANOVA † | A | Yes |
| Yildirim 2004 | A | A | B | 0 | Yes | Mann–Whitney U test | B | No |
| Asthma Clinical Research Centers 2007 | A | A | A | NA | Yes | Huber-White variance; Linear and logistic regression models |
A | Yes |
| Shah 2006 | A | A | A | 0 | Yes | ANOVA † | A | Yes |
| Bisgaard 2009 | B | B | A | 0 | Yes | Fisher's exact test | B | No |
| Chen 2021 | A | B | B | 5 | Yes | χ2 tests Pearson correlation test T test |
B | No |
| Prenner 2010-1 | B | B | C | 9 | Yes | NA§ | C | No |
| Prenner 2010-2 | B | B | C | 13 | Yes | NA§ | C | No |
A, low risk of bias: the study met almost criteria; B, moderate risk of bias: the study met part or unclear for one or more quality criteria; C, high risk of bias: the study was not met or included criteria; †ANOVA: analysis of variance; ‡ITT: Intention-to-treat; §NA: not available.