7. STOCK OPTION PLANS (Details 2)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Expected dividend yield	0.00%	0.00%
Minimum
Expected life	2 years 9 months	2 years 9 months
Expected volatility	71.97%	74.67%
Risk-free interest rate	2.08%	1.44%
Maximum
Expected life	3 years 6 months	3 years 6 months
Expected volatility	88.86%	95.30%
Risk-free interest rate	2.74%	1.92%

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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- Definition

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

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- Definition

Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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