pre_text: Employee Stock Purchase Plan The weighted average estimated fair value, as defined by the amended authoritative guidance, of rights issued pursuant to the Company’s ESPP during 2019, 2018 and 2017 was $4.28, $5.18 and $6.02, respectively. Sales under the ESPP were 24,131 shares of common stock at an average price per share of $9.76 for 2019, 31,306 shares of common stock at an average price per share of $15.40 for 2018, and 38,449 shares of common stock at an average price per share of $12.04 for 2017. As of December 29, 2019, 62,335 shares under the 2009 ESPP remained available for issuance. The Company recorded compensation expenses related to the ESPP of $60,000, $205,000 and $153,000 in 2019, 2018 and 2017, respectively. The fair value of rights issued pursuant to the Company’s ESPP was estimated on the commencement date of each offering period using the following weighted average assumptions: The methodologies for determining the above values were as follows: • Expected term: The expected term represents the length of the purchase period contained in the ESPP. • Risk-free interest rate: The risk-free interest rate assumption is based upon the risk-free rate of a Treasury Constant Maturity bond with a maturity appropriate for the term of the purchase period. • Volatility: The Company determines expected volatility based on historical volatility of the Company’s common stock for the term of the purchase period. • Dividend Yield: The expected dividend assumption is based on the Company’s intent not to issue a dividend under its dividend policy.
table: Fiscal Years
table: 2019 2018 2017
table: Expected life (months) 6.0 6.0 6.1
table: Risk-free interest rate 2.37% 2.26% 1.22%
table: Volatility 54% 50% 53%
question: Analyse this data from a financial earnings document. What is the average risk-free interest rate of the company's ESPP in 2017 and 2018?