Table II.

IRT-Based Reliability Function Across the Measurement Continuum

	# of items	Cronbach's alpha	IRT-based reliability
			Overall	T = 20	T = 30	T = 40	T = 45	T = 50	T = 55	T = 60	T = 70	T = 80
Higher scores, better well-being
Global Health	8	0.91	0.88	0.93	0.93	0.92	0.92	0.90	0.80	0.51	0.00	0.00
Relationship	31	0.95	0.96	0.97	0.97	0.97	0.97	0.97	0.95	0.91	0.63	0.00
Physical Activity	5	0.82	0.74	0.89	0.89	0.87	0.88	0.83	0.64	0.00	0.00	0.00
Curiosity	6	0.90	0.89	0.91	0.91	0.90	0.90	0.91	0.88	0.78	0.00	0.00
Persistence	6	0.90	0.86	0.87	0.87	0.85	0.86	0.86	0.85	0.85	0.70	0.00
Positive Affect	13	0.95	0.94	0.97	0.96	0.94	0.94	0.97	0.95	0.86	0.00	0.00
Flexibility	5	0.91	0.87	0.87	0.89	0.84	0.86	0.89	0.85	0.87	0.79	0.00
Frustration Tolerance	6	0.90	0.87	0.82	0.89	0.86	0.84	0.85	0.89	0.86	0.88	0.45
Higher score, worse symptom
Sleep Problems	16	0.95	0.95	0.00	0.60	0.91	0.94	0.95	0.95	0.95	0.95	0.94
Anger/Irritability	16	0.95	0.94	0.05	0.82	0.94	0.95	0.96	0.95	0.95	0.96	0.95
Anxiety	14	0.96	0.93	0.00	0.00	0.56	0.85	0.94	0.96	0.96	0.96	0.96
Depressive Symptoms	10	0.94	0.87	0.00	0.00	0.00	0.65	0.88	0.94	0.95	0.96	0.96

Note. Expected reliabilities which were estimated using simulation; T = 50 (SD = 10) is the average score for the general population.