Table 1.

The ORBIT (Outcome Reporting Bias In Trials) classification system for missing or incomplete outcome reporting in benefit outcomes. Figure 1 uses these classifications⁵

ORBIT classification	Description	Level of reporting	Risk of bias*
Clear that the outcome was measured and analysed
A	Trial report states that outcome was analysed but only reports that result was not significant (typically stating P>0.05)	Partial	High risk
B	Trial report states that outcome was analysed but only reports that result was significant (typically stating P<0.05)	Partial	No risk
C	Trial report states that outcome was analysed but insufficient data were presented for the trial to be included in meta-analysis or to be considered to be fully tabulated	Partial	Low risk
D	Trial report states that outcome was analysed but no results reported	None	High risk
Clear that the outcome was measured
E	Clear that the outcome was measured. Judgment says outcome likely to have been analysed but not reported because of non-significant results	None	High risk
F	Clear that the outcome was measured. Judgment says outcome unlikely to have been analysed	None	Low risk
Unclear whether the outcome was measured
G	Not mentioned but clinical judgment says likely to have been measured and analysed but not reported on the basis of non-significant results	None	High risk
H	Not mentioned but clinical judgment says unlikely to have been measured at all	None	Low risk
Clear that the outcome was not measured
I	Clear that the outcome was not measured	NA	No risk

NA=not appropriate.

^*Risk of bias arising from the lack of inclusion of non-significant results when a trial was excluded from a meta-analysis or not fully reported in a review because the data were unavailable.