Santerre 1996.

Methods	Study design: ITS
Participants	Physicians Clinical speciality: obstetrics and gynaecology Level of training: fully trained Setting/country: not clear/US
Interventions	In October 1988, the ACOG issued a physician practice guideline stating that a prior caesarean section was no longer a reason for performing a repeat section
Outcomes	1 process outcome: vaginal birth after previous caesarean section
Notes	‐
Risk of bias
Bias	Authors' judgement	Support for judgement
Intervention independent of other changes ‐ ITS	Unclear risk	No information was provided
Shape of Intervention effect pre‐specified ‐ ITS	Low risk	Quote, pg. 317: "the ACOG guideline essentially states that a previous birth by cesarean is no longer a good reason for doing one again in the future.  Consequently, if guidelines are effective at altering practice patterns, a noticeable increase in the VBAC rate should be detected after 1988 when the ACOG guideline was established"
Intervention unlikely to affect data collection ‐ ITS	Low risk	The intervention (ACOG guidelines) did not affect either the source or method of data collection
Blinding of outcome assessors (detection bias) ‐ ITS All outcomes	Low risk	The outcome was objective
Incomplete outcome data (attrition bias) ‐ ITS All outcomes	Low risk	The data set came from 55 Massachusetts hospitals from 1987 to 1991
Selective reporting (reporting bias) ‐ ITS	Low risk	All relevant outcomes in the methods section were reported in the results section
Other bias ‐ ITS	Low risk	There was no evidence of other risks of bias