Variables | Number of studies | Odds ratio | 95% confidence interval | p value |
---|---|---|---|---|
Diseases | Â | Â | Â | Â |
  Respiratory cancer | 30 | Ref. |  |  |
  Gastrointestinal cancer | 7 | 0.98 | 0.13 to 7.44 | 1.0 |
  Gynecological cancer | 19 | 0.38 | 0.09 to 1.56 | 0.2 |
  Head and neck cancer | 14 | 0.39 | 0.08 to 1.80 | 0.2 |
  Breast cancer | 10 | 0.23 | 0.04 to 1.46 | 0.1 |
Others | 58 | 0.23 | 0.07 to 0.76 | 0.02 |
Publication year | Â | Â | Â | Â |
  2002 | 14 | Ref. |  |  |
  2003 to 2006 | 38 | 0.11 | 0.02 to 0.53 | 0.01 |
  2007 to 2010 | 86 | 0.30 | 0.07 to 1.30 | 0.1 |
Sample size | Â | Â | Â | Â |
  Less than 24 | 30 | Ref. |  |  |
  25 to 49 | 50 | 1.43 | 0.47 to 4.35 | 0.5 |
  50 to 99 | 31 | 1.00 | 0.28 to 3.58 | 1.0 |
  Over 100 | 27 | 0.53 | 0.13 to 2.12 | 0.4 |
Study design | Â | Â | Â | Â |
  Retrospective study | 103 | Ref. |  |  |
  Prospective study | 35 | 2.78 | 1.05 to 7.35 | 0.04 |
Funding source | Â | Â | Â | Â |
  No description | 121 | Ref. |  |  |
  Description included | 17 | 2.9 | 0.78 to 10.73 | 0.1 |
Index type | Â | Â | Â | Â |
  Not indexed in MEDLINE | 69 | Ref. |  |  |
  Indexed in MEDLINE | 69 | 0.84 | 0.34 to 2.10 | 0.7 |
Comparative study | Â | Â | Â | Â |
  No | 72 | Ref. |  |  |
  Yes | 66 | 1.53 | 0.64 to 3.62 | 0.3 |