Studies by directionality and quality
| Direction of findings | Number of studies | Quality grading (%) |
|---|---|---|
| No association between IQ and BF | 21* | A—4 (19) |
| B—9 (43) | ||
| C—8 (38) | ||
| Positive association between IQ and BF | 28† | A—10 (36) |
| B—7 (25) | ||
| C—11 (39) | ||
| Initial positive association which became negative after adjustment for confounders | 18‡ | A—6 (33.3) |
| B—8 (44.4) | ||
| C—4 (22.3) | ||
| Initial positive association weakened after adjustment for confounders but remained statistically significant | 17§ | A—14 (82) |
| B—2 (12) | ||
| C—1 (6) |
*References: 24 ,25 ,30–32 ,35 ,36 ,39 ,54 ,56 ,62 ,63 ,73 ,74 ,86 ,87 ,89 ,91 ,97 ,100 ,101
†References: 9 ,15 ,21 ,27–29 ,37 ,38 ,42 ,48 ,51 ,57 ,59 ,61 ,64 ,68 ,71 ,72 ,75 ,79 ,82 ,85 ,90 ,94 ,95 ,98
‡References: 13 ,23 ,26 ,33 ,43–46 ,49 ,50 ,52 ,55 ,65 ,66 ,69 ,78 ,84 ,96
§References: 22 ,34 ,40 ,41 ,47 ,53 ,58 ,60 ,67 ,70 ,76 ,77 ,83 ,88 ,92 ,93 ,99
BF, breastfeeding.