	The lower age limit				The upper age limit
	${\bar{X}}_{i, \min}$	$S_{i, \min}$	Estimation interval under different confidence levels		${\bar{X}}_{i, \max}$	$S_{i, \max}$	Estimation interval under different confidence levels
	${\bar{X}}_{i, \min}$	$S_{i, \min}$	$z_{0.99}$	$z_{0.95}$	${\bar{X}}_{i, \max}$	$S_{i, \max}$	$z_{0.95}$	$z_{0.99}$
Handyman	19.37	3.244	19.12 - 19.61	19.18 - 19.55	39.29	7.067	38.88 - 39.69	38.75 - 39.82
Technician	22.24	4.288	21.93 - 22.55	22.00 - 22.48	41.22	6.402	40.87 - 41.58	40.76 - 41.69
Engineer	25.92	4.399	25.57 - 26.27	25.66 - 26.19	40.46	6.945	40.04 - 40.88	39.91 - 41.01
Manager	28.74	4.408	28.38 - 29.10	28.47 - 29.01	41.45	6.085	41.07 - 41.82	40.95 - 41.94