Ellertson 2003a.

Methods	Randomised, double‐blind, controlled trial Each dose of therapy was inserted in opaque gelatin capsules and then packaged in opaque envelopes labelled either "first dose" or "second dose" Following computer‐generated randomisation the pairs were inserted into sequentially‐numbered, opaque envelopes and sealed
Participants	2041 women at 5 centres in the US and UK within 72 h of a single, unprotected intercourse that occurred between 10 days before and 6 days after the estimated day of ovulation Included women aged 16‐45 years, willing to abstain further in the current cycle, could attend follow‐ups, keep a diary of side effects and refused the insertion of Cu‐IUDs Excluded women who had used hormonal contraception during the past 2 months, had not had 2 normal periods in the previous 2 cycles, breastfeeding and those who had a positive pregnancy test
Interventions	Standard 2‐dose Yuzpe regimen vs modified Yuzpe using norethindrone 2.0 mg instead of norgestrel 1.0 mg vs single dose of the standard Yuzpe regimen (followed 12 h later by a placebo)
Outcomes	Observed number of pregnancies, side effects, changes in menstrual pattern
Notes	ITT analysis reported Overall 3.3% lost to follow‐up; standard Yuzpe 21/696; modified Yuzpe 26/676; single‐dose Yuzpe 21/669
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	"Computer generated randomisation"
Allocation concealment (selection bias)	Low risk	"Population council staff enclosed each dose of each course of therapy in opaque gelatin capsules, and then packaged these capsules in opaque envelopes labeled either first dose or second dose. After computer generated randomisation, we inserted pairs of these envelopes into larger sequentially numbered envelopes, which we then sealed. Clinic staff simply gave each enrolled woman the next envelope in the sequence at that site."
Blinding (performance bias and detection bias) All outcomes	Low risk	"each dose of each course of therapy [placed] in opaque gelatin capsules". "Neither the clinic staff nor the women knew which regimens had been taken by which women until we broke the code at the end of the trial."
Incomplete outcome data (attrition bias) All outcomes	Low risk	ITT analysis was used
Selective reporting (reporting bias)	Low risk	All planned outcomes reported
Other bias	Low risk	None detected