Study ID	Outcome	High risk of bias (category A)a	High risk of bias (category D)b	High risk of bias (category E)c	High risk of bias (category G)d
Chlup 2009	ND
Barennes 2005	ND
Slama 1990	ND
Gunning 1978	ND
aClear that outcome was measured and analysed; study report states that outcome was analysed but reports only that result was not significant (Classification 'A', table 2, Kirkham 2010). bClear that outcome was measured and analysed; study report states that outcome was analysed but report no results (Classification 'D', table 2, Kirkham 2010). cClear that outcome was measured but was not necessarily analysed; judgement says likely to have been analysed but not reported due to non‐significant results (Classification 'E', table 2, Kirkham 2010). dUnclear whether outcome was measured; not mentioned, but clinical judgement says likely to have been measured and analysed but not reported on the basis of non‐significant results (Classification 'G', table 2, Kirkham 2010). ND: none detected.