Development and preliminary validation of the Glasgow Content of Thoughts Inventory (GCTI): a new measure for the assessment of pre-sleep cognitive activity.

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.