Objective: To develop a self-report measure (the Glasgow Content of Thoughts Inventory [GCTI]) for the assessment of pre-sleep cognitive activity in adults with sleep-onset insomnia.
Design: A psychometric, scale development approach was used.
Method: Over three consecutive nights, 12 people with insomnia provided 'live' audio-recordings of pre-sleep thought content, which were used to generate an item pool. The results were compared to the content and categorical structure of pre-sleep cognitive activity identified by Wicklow and Espie (2000), and commonalities in thought content were used to generate a draft scale. Following further piloting, a 25-item scale was developed and administered to two groups (29 people with insomnia and 29 good sleepers), along with other self-report measures, objective (actigraphic recordings) and subjective (diary) sleep indices, and results analysed to evaluate the psychometric properties of the scale.
Results: The GCTI demonstrated evidence of construct validity, successfully discriminated between individuals with insomnia and good sleepers, and was significantly correlated with existing measures of sleep disturbance. A score of 42 yielded a sensitivity of 100% and specificity of 83%. The GCTI demonstrated good test- retest reliability (ICC = .88) and internal consistency (alpha = .87).
Conclusions: The GCTI appears to be a valid and reliable instrument for use with patients with sleep-onset insomnia.