Study	Reason for exclusion
Adair 1992	Observational, non interventional study
Al‐Emran 2005	All participants received the same intervention, no control group
Cozza 2006	Longitudinal controlled study, where control group had no sucking habit
Cozza 2007	No randomisation
Degan 2005	No relevant outcomes reported
Friman 1986	Observational, non interventional study
Haryett 1970	Not an RCT
Woods 1999	Includes nail biters as well as digit suckers and not able to distinguish the results from the data. Issues with randomisation as the control group pretreatment is very different from the two treatment groups.

RCT: randomised controlled trial