Table 4.

Data quality in personal time trade-off (TTO) and tele-TTO interviews, with quality indicators adapted from [51]

Problematic responder types	Personal TTO (n = 36)		Tele-TTO (n = 113)		${\mathrm{\chi }}^2$	P-value
	N	%	N	%
All 6 health states same utility	0	0	0	0	–	–
One or more health state(s) ranked the same as 55555	8	22.2	32	28.3	0.25	0.62
One or more health state(s) ranked strictly lower than 55555	3	8.3	3	2.6	1.07	0.30
11211 same utility as 55555	0	0	0	0	–	–
Fewer than 4 distinct values	1	2.8	7	6.1	0.13	0.72
Utility of −1, −0.5, 0, 0.5 or 1 for all 6 health states	0	0	0	0	0	–
No negative utilities	6	16.7	13	11.4	0.29	0.59
No use of half-year increments in TTO	7	19.4	31	27.4	0.55	0.46

Problematic responses	Personal TTO (n = 216)		Tele-TTO (n = 678)		${\mathrm{\chi }}^2$	P-value
	N	%	N	%
Non-trading (utility of 1)	36	16.7	98	14.4	0.47	0.49
All-in trading (utility of − 1)	23	10.6	95	14.0	1.34	0.25
Strict violations of logical consistency (e.g. utility of 13313 > 24443)	8	3.7%	6	0.9	6.71	0.01
Weak violations of logical consistency (e.g. utility of 13313 ≥ 24443)	27	12.5	89	13.1	0.02	0.90