Landstar provides for the estimated costs of self-insured claims primarily on an actuarial basis. The amount recorded for the estimated liability for claims incurred is based upon the facts and circumstances known on the applicable balance sheet date. The ultimate resolution of these claims may be for an amount greater or less than the amount estimated by management. The Company continually revises its existing claim estimates as new or revised information becomes available on the status of each claim. Historically, the Company has experienced both favorable and unfavorable development of prior years’ claims estimates.

The following table summarizes the adverse effect of the increase in the cost of insurance claims resulting from unfavorable development of prior year self-insured claims estimates on operating income, net income attributable to Landstar System, Inc. and subsidiary and earnings per share attributable to Landstar System, Inc. and subsidiary set forth in the consolidated statements of income for the fiscal years ended December 25, 2021, December 26, 2020 and December 28, 2019 (in thousands, except per share amounts):


	Fiscal Years Ended
	December 25, 2021		December 26, 2020		December 28, 2019

Operating income	$	9,708	$	9,196	$	16,679
Net income attributable to Landstar System, Inc. and subsidiary	$	7,359	$	6,989	$	12,683

Diluted earnings per share attributable to Landstar System, Inc. and subsidiary	$	0.19	$	0.18	$	0.32

The unfavorable development of prior years’ claims in the fiscal year ended December 25, 2021 was primarily attributable to five claims. The unfavorable development of prior years’ claims in fiscal years ended December 26, 2020 and December 28, 2019 was attributable in each year to several specific claims as well as actuarially determined adjustments to prior year commercial trucking loss estimates.