Analyses of covariance with baseline values ( pain or disability ) as covariates showed that transcranial direct current stimulation was ineffective for the reduction of pain ( difference between groups on visual analogue scale @ mm ( @ % confidence interval -@ mm to @ mm ; P = @ ) ) and disability ( difference between groups @ point ( -@ to @ ; P = @ ) ) and did not influence the outcome of cognitive behavioural management ( difference between group @ mm ( -@ mm to @ mm ) ; P = @ ; difference between groups on Oswestry disability index @ point ( -@ to @ ) ; P = @ ) .