The previous post has given me some inspirations. Actually, what statistical methods can be used to assess the reliability of a scale used to measure relapse behaviour of a drug user, and what do these methods measure?

Glad to learn it.

It is informative and I really appreciate it.

Statistical methods used to assess the reliability of a scale used to measure relapse behaviour of a drug user include Cronbach's alpha, intra-class correlation, and Cohen's kappa. These methods measure different aspects of reliability, such as internal consistency, inter-rater agreement, and test-retest stability.