<qa>  How many months are participants assigned to group treatment?The purpose of this study is to compare three methods of delivering behavioral weight loss treatment.Participants are randomly assigned to one of three 18-month weight loss treatments group, individual, or smartphone treatment. Participants who are assigned to group treatment will attend group meetings weekly for the first 6 months, then every 2 weeks for 6 months, and then monthly for the final 6 months. Participants who are assigned to individual treatment will attend one-on-one sessions with a weight loss counselor every month for 18 months. Participants who are assigned to smartphone treatment will use a smartphone to learn and practice weight loss skills. They will also attend one-on-one sessions with a weight loss counselor every month for 18 months. Assessment visits are conducted at baseline, 6, 12, and 18 months. 