Time to readiness for discharge is a valid and reliable measure of short-term recovery after colorectal surgery.
Short-term recovery after colorectal surgery has been traditionally investigated through length of stay (LOS). However, this measure is influenced by several confounding factors. This study aimed to investigate the construct validity and reliability of assessing the time to achieve standardized discharge criteria (time to readiness for discharge, or TRD) as a measure of short-term recovery. In a secondary analysis, we compared sample size requirements for randomized controlled trials (RCTs) using TRD or LOS as outcome measures. Seventy patients participated in the construct validity study and 21 patients participated in the reliability study. TRD was defined as the number of days to achieve discharge criteria previously defined by consensus. Construct validity was investigated by testing six hypothesis based on the assumption that TRD measures short-term recovery. Reliability was calculated by comparing measures of TRD by two independent assessors. Variability estimates (standard deviations) of LOS and TRD were used for sample size calculations. Five of the six hypotheses were supported by the data (p < 0.05). Interobserver reliability was excellent (ICC2.1 = 0.99). Sample size estimations showed that RCTs using TRD as an outcome measure require approximately 23 % less participants compared to RCTs using LOS. The results of this research support the construct-validity and reliability of TRD as a measure of short-term recovery. Using TRD as an alternative to LOS may reduce sample size requirements in future RCTs.