Selim 2012.

Study characteristics
Methods	Randomised controlled trial Duration and location of the trial: not stated
Participants	Inclusion criteria: diagnosis of PCOS based on Rotterdam criteria provided that anovulation is 1 of the 2 required criteria Exclusion criteria: quote: "exclusion criteria included hyperprolactinaemia, congenital adrenal hyperplasia, thyroid disease, other causes of amenorrhoea such as premature ovarian failure, and clinically suspected Cushing’s syndrome or androgen‐secreting neoplasm. Exclusion criteria also included all women who had received metformin or LOD in the previous 6 months. Other causes of infertility were excluded by documentation of a normal uterine cavity and at least one patent fallopian tube, and each woman’s current partner had a semen concentration of at least 20 x 106/mL Number of centres: not reported Number of women randomised: 220; group A letrozole: 110, group B CC: 110 Number of women analysed: group A letrozole: 102, group B CC: 99 Number of withdrawals/exclusions/loss to follow‐up and reasons: quote: "In the letrozole group, eight women were excluded because of missed follow‐up visits (three women), treatment suspension (two women), and homogenous not triple‐line endometrial pattern (three women). In the CC group, 11 women were excluded because of missed follow‐up visits (four women), treatment suspension (two women), and homogenous not triple‐line endometrial pattern (five women)." Age (y): group A letrozole: 26.0 ± 2.7, group B CC: 25.1 ± 3.1 BMI (kg/m²): group A letrozole: 24.4 ± 4.3, group B CC: 23.8 ± 3.7 Duration of infertility (y): group A letrozole: 2.9 ± 0.6, group B CC: 2.6 ± 0.7 Country: Saudi Arabia
Interventions	Group A: 110 participants treated with 5 mg/day of letrozole (Femara; Novartis, Switzerland) in 2 divided doses from cycle day 3‐7 Group B: 110 participants treated with 100 mg/day of CC (Clomid; Sanofi Aventis, France) in 2 divided doses from cycle day 3‐7
Outcomes	Quote: "The mean number of follicles, endometrial thickness, the Doppler study of endometrial and sub endometrial vasculatures, ovulation rate, and pregnancy rate were compared in both groups."
Notes	Ethical approval: quote: "approval was obtained from the Institutional Review Board of Jeddah Clinic Hospital, Jeddah, Saudi Arabia." Informed consent: yes, quote: "all participants gave verbal and written informed consent." Source of funding: not stated Conflicts of interest: quote: “No competing financial interests exist.” Power calculation: not stated
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Unclear how envelopes were numbered
Allocation concealment (selection bias)	Low risk	Participants were randomly allocated to the letrozole group or CC group by means of a series of blind envelopes numbered from 1 to 220. Each participant was invited to choose an envelope and was placed by the clinic secretary in either the letrozole group or the CC group.
Blinding of participants and personnel (performance bias) All outcomes	High risk	Quote: "The patients were not blinded about the treating drug in either group."
Blinding of outcome assessment (detection bias) All outcomes	Low risk	To remove any inter‐observational bias, ultrasound on all participants was demonstrated by a single observer (MF Selim) who was blinded to the treating drug.
Incomplete outcome data (attrition bias) All outcomes	Low risk	All dropouts were reported, reasons given
Selective reporting (reporting bias)	Low risk	All expected outcomes were reported.
Other bias	Low risk	None