Table 1 The modified Royal College of General Practitioners (RCGP) three-star system of the British Occupational Health Research Foundation

***

Strong evidence – provided by generally consistent findings in multiple, high quality, scientific studies.

**

Moderate evidence – provided by generally consistent findings in fewer, smaller or lower quality, scientific studies.

*[*]

Moderate evidence – provided by generally consistent findings in fewer, smaller or lower quality, scientific studies, based on questionnaire-conducted studies or other weak evidence (i.e. clinical weakness due to absence of LFT, sPFT, SIC)

*

Limited or contradictory evidence – provided by one scientific study (analytic) or inconsistent findings in multiple scientific studies.

[*]

Limited or contradictory evidence – provided by one scientific study (analytic) or inconsistent findings in multiple scientific studies, based on questionnaires or other weak evidence ( i.e. clinical weakness due to absence of LFT, sPFT, SIC)

(*)

Very limited or contradictory evidence – provided by at least three case reports, one case series, one non-analytic study or one occupational disease statistical study with at least five asthma cases

-

No scientific evidence – based on clinical studies, theoretical considerations and/or clinical consensus