It is debated whether cognitive behaviour therapy (CBT) or graded exercise therapy (GET) reliably facilitate recovery in chronic fatigue syndrome (CFS). As such, any data on this issue, such as those presented by White et al. (Reference White, Goldsmith, Johnson, Chalder and Sharpe2013), are always of interest.

The trial was not blinded, however, with participants, therapists and research assessors aware of the treatment group for each individual (White et al. Reference White, Sharpe, Chalder, DeCesare and Walwyn2007). Consequently, there is the possibility of significant response bias. Indeed, while the CBT group performed better than the adaptive pacing therapy (APT) and the specialist medical care only (SMC) groups on the self-rated SF-36 physical functioning (SF-36 PF) scale, there were no significant differences and minimal numerical differences on the more objective six-minute walk distance test (6MWD) (White et al. Reference White, Goldsmith, Johnson, Potts, Walwyn, DeCesare, Baber, Burgess, Clark, Cox, Bavinton, Angus, Murphy, Murphy, O'Dowd, Wilks, McCrone, Chalder and Sharpe2011).

This discrepancy between subjective and objective outcome measures is not a novel finding in the CFS literature. Wiborg et al. (Reference Wiborg, Knoop, Stulemeijer, Prins and Bleijenberg2010) analysed three randomized control trials (RCTs) of three CBT interventions, finding that while fatigue was improved in the CBT groups compared to waiting-list controls, there was no difference in actometer readings between the two groups. Moreover, a mediation analysis showed changes in physical activity were not related to changes in fatigue. Similarly, in a GET RCT, Moss-Morris et al. (Reference Moss-Morris, Sharon, Tobin and Baldi2005) found that an increase in physical fitness did not mediate the treatment effect of reduced fatigue. In an uncontrolled trial of a graded activity programme, Friedberg & Sohl (Reference Friedberg and Sohl2009) reported improvements in SF-36 PF and fatigue while actometers showed overall reduction in total activity levels.

The 6MWD is one objective outcome measure White et al. (Reference White, Goldsmith, Johnson, Chalder and Sharpe2013) could have incorporated into their recovery criteria (White et al. Reference White, Sharpe, Chalder, DeCesare and Walwyn2007). Reference ranges for 6MWDs, which adjust for gender and age inter alia, exist for healthy adults (e.g. Chetta et al. Reference Chetta, Zanini, Pisi, Aiello, Tzani, Neri and Olivieri2006; Casanova et al. Reference Casanova, Celli, Barria, Casas, Cote, de Torres, Jardim, Lopez, Marin, Montes de Oca, Pinto-Plata and Aguirre-Jaime2011). Then, after calculating the new recovery percentages with the 6MWDs, analyses could be preformed to compare the means with predicted values.