Table 4.

Articles that developed MCDM methods in the context of COVID-19 under fuzzy environment.

Authors	Fuzzy sets (uncertainty theories)	Frequency
Chen and Lin [107 ], Hosseini et al. [114 ], Manupati et al. [77 ], Das et al. [115 ], Majumdar et al. [116 ], Shah et al. [121 ], Lin et al. [5], [6], Choudhury et al. [124 ], Yao [130 ], Özkan et al. [10 ], Kumar et al. [133 ], Chen and Wang [143 ], Palouj et al. [144 ], Altay et al. [71 ], Razzaq et al. [8 ], Orji and Ojadi [152 ], Karmaker et al. [153 ], Mahmoudi et al. [155 ], Sharma et al. [157 ], Asadi et al. [139 ], Samanci et al. [145 ]	Type-1 fuzzy set	21
Ocampo and Yamagishi [104 ], Ecer and Pamucar [118 ], Ocampo et al. [119 ], Goker [125 ], Alam et al. [141 ]	Intuitionistic fuzzy set	5
Mardani et al. [102 ], Saraji et al. [117 ], Mishra et al. [123 ], Ghorui et al. [131 ]	Hesitant fuzzy set	4
Paul et al. [140 ], Petrudi et al. [134 ], Shanker et al. [142 ], Mehmood et al. [151 ]	Grey theory	4
Ashraf and Abdullah [103 ], Ashraf et al. [109 ], Alsalem et al. [146 ]	Spherical fuzzy set	3
Boyacıand Şişman [126 ], Albahri et al. [147 ]	Pythagorean fuzzy set	2
Aydin and Seker [120 ], Wan et al. [93 ]	Interval type 2 fuzzy set	2
Alkan and Kahraman [112 ], Khan et al. [16], [17]	q-rung orthopair fuzzy set	2
Chai et al. [127 ], Xiaozhen et al. [158 ]	Z-number	2
Hezam et al. [135 ]	Neutrosophic set	1
Kirişci et al. [70 ]	Pythagorean fuzzy soft set	1
Belhadi et al. [106 ]	Interval-valued fuzzy set	1
Wen and Liao [156 ]	Probabilistic linguistic term set	1