Table 3.
SELECTION BIAS |
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Method of recruiting subjects (healthy participant, non-healthy participant, with or without treatment participants). |
Duration and severity of the addiction or related disorder. Stage of treatment prior to tDCS (detoxification or continuation of substance use). |
OBSERVATION BIAS |
Over or underestimating the intensity of craving. |
Placebo effect of tDCS itself. |
Placebo effect of therapeutic trials carried out in the field of addiction and related disorders. |
Order of the placebo session and active session in a crossover study. |
Insufficient number of pulses and number of sessions. |
Attrition bias (drop out). |
CONFOUNDING BIAS |
Sociodemographic characteristics: age, gender, ethnicity. |
Hormonal status. |
Volume of gray matter. |
Psychiatric and somatic comorbidities. |
Handedness. |
Psychotropic treatments (in particular, continuation of anti-craving drugs during the trial). |
Duration of the session, which may overlap with the duration required for the craving to subside naturally. |
Cumulative and persistent effects of tDCS when the interval between two sessions is very short. |
Sample size. |
Ability of the treatment-seeking participants to use relapse prevention techniques during cue-induced craving procedure. |
All these biases are discussed in Sections Methodological Issues and Technical Issues.