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Stock option plan (Tables)

12 Months Ended

Dec. 31, 2020

Stock option plan

Schedule of assumptions used in valuation of stock options

		Year ended December 31,
		2020		2019		2018
Expected volatility		78.9% ‑83.8%		73.5% ‑74.5%		71.5%
Risk‑free rate		0.36% ‑1.43%		1.53% ‑2.63%		2.9%
Expected dividend yield		0%		0%		0%
Expected term in years		5.50-6.08		6.08-7.59		8.20

Summary of stock option activity

					Weighted‑			Weighted
					average			average
					exercise			remaining		Aggregate
		Number of			price per			contractual		intrinsic
		options			share			term (in years)		value
Outstanding at January 1, 2018			1,897,206		$	1.46		8.3
Granted			24,067			1.01
Exercised			(2,306)			0.92
Cancelled/Forfeited			(74,779)			17.31
Outstanding at December 31, 2018			1,844,188		$	0.82		7.6
Granted			2,018,796			8.82
Exercised			(322,267)			0.23
Cancelled/Forfeited			(40,783)			0.99
Outstanding at December 31, 2019			3,499,934		$	5.49		7.5
Granted			446,800			35.16
Exercised			(164,075)			0.92
Cancelled/Forfeited			(11,200)			38.78
Outstanding at December 31, 2020			3,771,459		$	9.10		6.8		$	6,945,112
Exercisable at December 31, 2020			1,968,116		$	3.52		6.1		$	5,602,168
Vested or expected to vest at December 31, 2020			3,771,459		$	9.10		6.8		$	6,945,112

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Tabular disclosure for stock option plans. Includes, but is not limited to, outstanding awards at beginning and end of year, grants, exercises, forfeitures, and weighted-average grant date fair value.

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Tabular disclosure of the significant assumptions used during the year to estimate the fair value of stock options, including, but not limited to: (a) expected term of share options and similar instruments, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions.

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