Study	Reason for exclusion
Akbari 2012	No PCOS
Al‐Hussaini 2014	Only short conference abstract; we did not find a published study article. We were unable to retrieve any information from study authors.
Al‐Shaikh 2017	Not a RCT
Angel 2014	RCT, but not about women with PCOS
Anwary 2012	Not a RCT
Azargoon 2012	Not a RCT
Azmoodeh 2015	No PCOS
Badawy 2009c	Not a RCT
Baruah 2009	Quasi‐randomised trial (quote: "Based on attendance order, patients with odd numbers were given letrozole and those with even numbers were given CC")
El Bigawy 2008	Quasi‐randomised trial
Foroozanfard 2013	Not randomised for clomiphene or letrozole
Khanna 2013	Not a RCT, no PCOS
Li 2016	Not randomised for letrozole
Mittal 2004	Not a RCT
Nahid 2012	Suspected quasi‐randomisation based on attendance order
NCT00610077	No published data found, last updated on clinicaltrials.gov in 2008. No response from study authors.
NCT01315912	Not a RCT
NCT01431352	For the 2018 update, there was no update on clinicaltrials.gov. No study data available, and no response from authors.
NCT01577017	No study results found, unable to obtain more information from study authors
NCT01679574	Study should be finished. We contacted authors by email found through Google because no contact information was written in the study protocol: abd_ellah98@yahoo.com. For the 2018 update, there was no update on clinicaltrials.gov and still no response from the author.
NCT01793038	Unable to obtain information from study authors. No study data found, no update on clinicaltrials.gov.
Ozdemir 2013	RCT, but not about women with PCOS
Pakrashi 2014	Not randomised for letrozole
Palihawadana 2015	Women with PCOS were excluded from the study
Pourali 2017	Women with PCOS were excluded from the study
Sarvi 2010	Not randomised for letrozole
Sharma 2010	Only conference abstract available, full article could not be found. Contact address of authors unknown
Xi 2015	Not a RCT
Yang 2008	Not a RCT (Quote: "the allocation depended on the patients' choice" ‐ translated by Prof Taixiang Wu)
Yun 2015	Not a RCT