Table 1. Overview of the studies

Study	Authors	Etiology of olfactory dysfunction	Number of patients	Length of training	Results (%)
1	Hummel et al. (2009)1)	Postinfectious, posttraumatic, idiopathic	56	12 weeks	>6 TDI score: training (30%)
2	Fleiner et al. (2012)25)	Sinonasal, postinfectious, posttraumatic, idiopathic	46	35 weeks	>6 TDI score: training+topical steroid (33%)
3	Konstantinidis et al. (2013)20)	Postinfectious, posttraumatic	119	16 weeks	>6 TDI score: training (postinfectious 68%, posttraumatic 33%)
4	Damm et al. (2014)30)	Postinfectious	144	16 weeks	High concentration training (63%), low concentration training (19%)
5	Geißer et al. (2014)24)	Postinfectious	39	32 weeks	>6 TDI score: training (56%)
6	Schriever et al. (2014)21)	Aging	91	12 weeks	No significant results
7	Jung et al. (2019)18)	Postinfectious, posttraumatic, idiopathic	134	12 weeks	>6 TDI score: training+topical steroid (55.2%)
8	Choi et al. (2021)12)	Postinfectious	104	12 weeks	Significance results in TDI score compare to no training group

TDI: threshold-discrimination-identification.