Table 1.

Available data and measures.

Data Item	Questionnaire	Information on measurement
Depression	Patient Health Questionnaire 9-item (PHQ-9) (Kroenke et al., 2001)	To measure symptoms of depression, scores of 10 or above indicate clinical caseness for depression, and a reduction of 6 or more points is used to indicate reliable improvement (NHS Digital, 2016).
Anxiety	The Generalized Anxiety Disorder Scale 7-item version (GAD7) (Spitzer et al., 2006)	To assess generalized anxiety symptoms, a cut-off of 8 or higher is used for caseness and 4 or more for reliable improvement. Alternative “anxiety disorder specific measures” (ADSMs) are used when specific anxiety disorders are identified as the “problem descriptor” (Clark, 2018), for example the Social Phobia Inventory (Connor et al., 2000) for use when social anxiety disorder is identified. When present, these ADSMs are used to calculate outcomes instead of the GAD-7. The full list of ADSMs alongside the service thresholds for caseness and reliable change is presented in Appendix B and further details are available in the annual reports on the UK IAPT programme (NHS, 2018).
Personal functioning	The Work and Social Adjustment Scale (WSAS) (Mundt et al., 2002)	Measures personal functioning in relation to: ‘ability to work’, ‘home management’, ‘social activities’, ‘private leisure activities’ and ‘close relationships’ (domain score range, 0-8). The WSAS item on the ‘ability to work’ is routinely recorded as “not applicable” for individuals not in employment, as was the case for 85% of older adults in the present study sample. As a result, this item was excluded from the analyses.
Phobic anxiety	The IAPT Phobia Scales (National IAPT Programme Team, 2011)	Consist of three questions each assessing the degree of avoidance of certain situations related to different types of phobic anxiety - agoraphobia, social phobia and specific phobias
Problem descriptor	N/A	The services collect data on each patient's problem descriptor (ICD-10 code), representing a probable or confirmed diagnosis, in order to match patients to evidence-based treatments. We categorised problem descriptors following conventions from previous studies that used similar data (Buckman et al., 2018): depression; mixed anxiety and depression; generalized anxiety disorder; obsessive compulsive disorder; post-traumatic stress; phobic anxiety and panic. In addition, bereavement was kept as a separate category due to its expected prevalence in the older adult population.
Demographics	N/A	Self-reported gender at point of referral, age, index of multiple deprivation (IMD) decile and ethnicity (based on UK census codes ‘White’, ‘Mixed’, ‘Asian’, ‘Black’, ‘Chinese’ and ‘other’) were available in the dataset.
Long-term health conditions	N/A	All patients are asked whether or not they have any long-term physical health condition (LTC). The type of condition was not available in the dataset.
Medication	N/A	At every clinical contact with their patients clinicians in the services routinely record whether their patients were prescribed psychotropic medication(s).
Treatment factors	N/A	The number of “Low Intensity” (LI) and “High Intensity” (HI) treatment sessions received; the number of days between referral to the service and assessment, and the number of days between the assessment and first treatment session. Days between referral and sessions, and days between assessment and first treatment session were winsorized at the top 99% due to a limited number of extreme values.