Table 1 Characteristics and methods used in the evaluated meta-analysis papers

Environmental tobacco smoke

Leonardi-Bee et al. 2008 [18]

58

MEDLINE, EMBASE, CINAHL, LILACS

yes

yes

yes

Random

yes

Salamasi et al. 2010 [19]

76

139 K

Medline, EMBASE, reference lists

yes

yes

yes

Random

yes

yes

Leonardi-Bee et al. 2011 [20]

19

MEDLINE, EMBASE

yes

yes

yes

Random

yes

yes

Outdoor air pollution

Sapkota et al. 2010 [16]

20

Up to 1.9 M

ISI Web of Knowledge, PubMed

yes

yes

both

yes

yes

yes

Vrijheid et 2011 [21]

10

Up to 5.4 M

MEDLINE ISI Web of Science

yes

both

yes

yes

Indoor air pollution

Pope et al. 2010 [22]

8/4

18 K/34 K

MEDLINE, EMBASE, Cochrane Controlled Trials Register Cumulative Index to Nursing and Allied Health Literaturee, Latin American and Caribbean Health Sciences Information System, System for Information on Grey Literature in Europe, Index to Conference Proceedings, PASCAL

yes

yes

yes

both

yes

yes

yes

yes

Water contaminants

Hwang et al. 2008 [23]

6

Up to 3.3 M

PubMed

yes

both

yes

Nieuwenhuijsen et al. 2009 [24]

15

Up to 3.6 M

PubMed Review articles

yes

both

yes

yes

yes

Grellier et al. 2010 [25]

15

Up to 1.6 M

MEDLINE

yes

no

yes

both

yes

yes

yes

Nieuwenhuijsen et al. 2010 [17]

5

MEDLINE

POPs/PCB

Govarts et al. 2012 [26]

12

8 K

European birth cohorts http://www.enrieco.org

yes

both

yes

Occupation

Logman et al. 2005 [27]

6

384 K

MEDLINE Toxline, Reprotox, EMBASE

yes

yes

both

yes

yes

Romitti et al. 2007 [28]

7/5

3.5 K/64 K

MEDLINE

Random

yes

Rocheleau et al. 2009 [29]

9

376 K

PubMed

Random

yes

Pesticides

Ngo et al. 2006 [30]

22

196 K

MEDLINE, EMBASE

yes

yes

both

yes

yes

yes

Ngo et al. 2010 [31]

7

135 K

MEDLINE, EMBASE

no

yes

yes

both

yes

yes

yes