Table 1.

Issues to be considered for assessing a rising tide phenomenon and results of assessment for the four case studies*

	SPI2	Critical pathways	EQHIV	MERIT
Positive evidence
Direct evidence
Improvement in process and/or outcome measures observed in external sites:	Yes	Yes	Yes	Yes
Timing: before or during evaluation study	Before and during	Before and during	Before	During
System-wide or specific external site(s)	System-wide	Specific external sites	System-wide	System-wide (but 30% participation)
Qualitative evidence showing behaviour changes driven by external factors in both study groups	Yes	Yes	Yes	Yes
Suggestive evidence
Baseline measures better than expected, or already showing high standards or improving trend	Yes	Yes	Yes	Yes
Circumstantial evidence
Heightened awareness of the problems	Yes	Yes	Yes	Yes
Negative evidence†
Contamination within study	No	No	Unlikely	Unlikely
Other potential sources of biases‡	Not apparent	Not apparent	Attrition bias cannot be ruled out	Not apparent

*Improvement in process and/or outcome measures were observed in both intervention and control groups in these studies during the evaluation period.

†Factors of which the impact on study findings could resemble a rising tide phenomenon.

‡Including selection bias (eg, control group being a selective sample of highly motivated units or having more headroom for improvement), bias in outcome assessment (eg, changes in methods of data collection or coding over time) and attrition bias (eg, poor-performing units dropping out and being excluded from analysis).