Treatment effect bias in randomised controlled trials using surrogate outcomes: a preliminary cohort study analysis

Table 2 Comparison of outcome results.

	Surrogate Trials (N=138) N (%)	Final Trials (N=132) N (%)	*P-value* ^a
Study outcome ^b			0.006 ^c
Positive	49 (36)	41 (31)
Negative	5 (4)	4 (3)
Neutral	32 (23)	65 (49)
Risk of bias
Statement of ITT	95 (69)	106 (80)	0.031
Automated sequence generation	82 (59)	93 (70)	0.058
Allocation concealment	96 (70)	97 (63)	0.476
Blinding/Placebo	72 (52)	60 (45)	0.27

^aChi-square test, unless otherwise specified.
^b‘positive’: treatment group superior to control (P≤0.05); ‘negative’, control group superior to treatment (P≤0.05); ‘neutral’, treatment and control indifferent, P>0.05).
^cFisher’s exact test. Multiple-interventions trials are excluded from this comparison.

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