Group CBT with IPT will consist of 20 weekly two-hour sessions and has been developed for the proposed study based on the protocols for group CBT for HD and group IPT. Treatment includes strategies from CBT, including cognitive restructuring, behavioral exposures, and organizational strategies, as well as strategies from IPT, including role-play, interpersonal skills building, communication analysis, and decision analysis.

Group treatment designed to target relationships with both possessions and people.

The Hoarding Rating Scale is a commonly used measure of hoarding symptoms in which participants rate the severity of their symptoms. Minimum score is 0 and maximum score is 40. Higher scores indicate more severe/worse symptoms.

The Reciprocal Attachment Questionnaire Adapted assesses attachment to one's belongings, with higher scores indicating greater attachment to possessions (i.e., worse outcome). Minimum score is 75 and maximum score is 375.

The AAS is a measure of two dimensions proposed to underlie interpersonal attachment security: anxiety and avoidance. Higher scores indicate worse outcomes. Minimum score is 0 and maximum score is 72.

The INQ is a measure of two interpersonal risk factors, namely perceived burdensomeness and thwarted belongingness, with higher scores indicating higher levels of each construct (i.e., worse outcome). Minimum score is 15 and maximum score is 105.