Evidence at a glance: error matrix approach for overviewing available evidence

Table 3 Ordering of evidence according to levels of evidence (systematic error), standard error (random error), and outcome measures (design error) in peri-operative beta-blockade versus placebo for major non-cardiac surgery (example 1).

	Level of evidence	Standard error
		All-cause mortality	Cardiovascular mortality	Non-fatal myocardial infarction	Non-fatal stroke
Bangalore [50]	1a	0.12	0.16	0.10	0.28
Poise [51]	1b	0.13	0.17	0.10	0.33
MaVS [52]	1b	1.07	Z	N	0.66
Dipom [53]	1b	0.34	0.48	0.91	Z
Mangano [54]	1b	0.85	1.22	1.22	1.11
Bangalore [50]	1c	0.11	0.15	0.09	0.28
Wetterslev [55]	1c	0.24	N	0.23	N
Poldermans [56]	1d	0.76	0.76	Z	N
Lindenauer [57]	2b	0.02	N	N	N
AHA Guidelines [58]	5	N	N	N	N

Z: outcome with zero-events in one or both treatment arms which makes SE incalculable; N: no data
Some outcome measures may be correlated (e.g. cardiovascular mortality is included in all-cause mortality).
In this example the formulas for SE of lnRR_i for individual studies and SE of lnRR_MH for meta-analysis were used.

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