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| Theory | Country | Frequence | Authors |
|---|---|---|---|
| TAM | Germany; Jordan | 3 | [30–32] |
| Extended TAM | India; Thailand; Indonesia; Malaysia; Greece; China | 3 | [33–35] |
| DOI | Germany, Jordan | 2 | [30,32] |
| TPB | Jordan | 1 | [32] |
| Extended TPB | Germany, | 1 | [36] |
| Empirical models | South Korea; United Kingdom; China; France; Germany; Italy; Poland; Romania; Spain; Sweden | 5 | [3,6,37–39] |
