“…In order to provide a report, we group the size of the studies into four categories: less than 200 consumers, between 200 and 500 consumers, between 500 and 1000 consumers, and more than 1000 consumers. It emerges that 31.1% of the studies involve a sample with a size of less than 200 consumers [ 27 , 28 , 31 , 36 , 48 , 52 , 53 , 56 , 57 , 58 , 62 , 66 , 67 , 68 ], 33.3% of the studies involve a sample with a size between 200 and 500 consumers [ 30 , 36 , 39 , 40 , 42 , 43 , 44 , 45 , 46 , 49 , 59 , 60 , 63 , 64 , 69 ], 22.2% of the studies involve a sample with a size between 500 and 1000 consumers [ 29 , 32 , 33 , 37 , 41 , 47 , 51 , 61 , 70 ] and only 11.11% of the studies involve a sample with a size more than 1000 consumers [ 34 , 38 , 54 , 55 , 65 ]. In 8.8% of the reviewed studies, the sample size is not declared [ 7 , 8 , 9 , 50 ].…”