| | | 2017 | | 2016 | | 2015 | | |||
| Risk-free interest rate | | | 0.78% - 1.74 | % | | - | | | 0.78% - 1.68 | % |
| Dividend yield | | | 0 | % | | - | | | 0 | % |
| Volatility | | | 97 | % | | - | | | 86 | % |
| Forfeiture rate | | | 21 | % | | - | | | 23 | % |
| Estimated expected lives | | | 5 years | | | - | | | 5 years | |