Income Taxes



	Three months ended March 31,
	2018		2017
	(In millions)
Income tax provision	$	4.7	$	3.3

In the three months ended March 31, 2018, the income tax provision was $4.7 million for an effective tax rate of 25.1%. The Company’s effective tax rate differed from the 21% statutory federal income tax rate primarily due to state income taxes and certain expenditures which are permanently not deductible for tax purposes, partially offset by the impact of R&D credits.

In the three months ended March 31, 2017, the income tax provision was $3.3 million for an effective tax rate of 35.9%. The Company’s effective tax rate differed from the 35% statutory federal income tax rate primarily due to state income taxes and certain expenditures which are permanently not deductible for tax purposes, offset by the impact of R&D credits and excess tax benefits from the exercise and vesting of stock-based compensation.

See a discussion of the significant increase in the income tax payable balance in Note 5(f).

A valuation allowance is required when it is more-likely-than-not that all or a portion of deferred tax assets may not be realized. Assessing the need for a valuation allowance requires management to evaluate, on a quarterly basis, all available evidence, both positive and negative. As of March 31, 2018, the Company continues to believe that the weight of the positive evidence outweighed the negative evidence regarding the realization of its net deferred tax assets.