Table 1

Study cohort characteristics

Publications for each unique study	Start and end of study	Type of study	Countries	Sample size*	Age† (years), mean (SD)	Male (%)	Modes of contact ever used in follow-up?	Time points for follow-up (months)	Retention rate Primary definition‡(%)	Retention rate Secondary definition§ (%)
Aitken et al23	June 2008– August 2012	Cohort	Australia	112 105	40 (20)	83	Phone, mail	1 6	76 72	83 84
Christensen et al18	August 2005–December 2008	Cohort	USA and 26 countries	472	38 (14)	77	Not reported	3	72	74
Richards et al24 25 37	July 2006–July 2008	Cohort	USA	160	43 (17)	57	In person	12	67	68
Orwelius et al26	August 2000–June 2006	Cohort	Sweden	108 83	44 (18)	68	Mail	12 24	79 54	79 69
Schnyder et al27 28	January 1996–June 1998	Cohort	Switzerland	120	38 (13)	74	Not reported	12	88	88
Tøien et al29 30	June 2005–December 2007	Cohort	Norway	148 147	40 (16)	70	Mail	3 12	79 79	80 80
Hepp et al31 32	January 1996–June 2003	Cohort	Switzerland	121 106 90	38 (13)	74	Not reported	6 12 36	88 88 74	88 100 100
Davydow et al33	July 2001–September 2003	Cohort	USA	1781	41 (32)	71	Phone	12	83	83
Frutiger et al34	1980–1988	Cohort	Switzerland	177	36 (17)	81	In person, other	60	94	94
Holbrook et al35	January 1990–June 1990	Cohort	USA	–	30 (13)	74	Phone	3	NA¶
Mackenzie et al36	July 1982–March 1984	Cohort	USA	–	27 (7)	78	In person, phone	6 12	NA NA

*Sample size was calculated as the number of ICU survivors eligible for follow-up at hospital discharge. For studies that did not provide this information we used the sample size at start of the study, and for studies that did not provide either we used the sample size after informed consent was obtained. In cases where there were articles published while the study was still ongoing, we used the article with the largest sample size.
†Age was expressed as mean (SD) or median (IQR).
‡Primary participant retention rates were calculated as the number of participants assessed at each follow-up time point divided by the number presumed alive and eligible for assessment at that time point (this included the participants who withdrew and withdrawn just prior to the time point).
§Secondary participant retention rates were calculated after a sensitivity analysis where we calculated the number of participants assessed at each follow-up time point divided by the number alive and eligible for assessment at the time point (this did not include the participants who died, withdrew, and withdrawn just prior to the time point).
¶Retention rates could not be calculated because mortality was combined with loss to follow-up.
ICU, intensive care unit; NA, not applicable;