Study Design

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SOS originally consisted of one registry study and one intervention study (2). Later one randomized reference study and one genetic sib pair study were added.

In the registry study 6000-7000 obese men (BMI > 34) and women (BMI > 38) in the age range 37-60 years are examined by GPs at 480 of the 700 existing primary health care centres in Sweden. From the registry, patients are recruited into the intervention study consisting of one surgically treated group (goal n = 2000, February 2000, n = 1870) and one matched control group (same numbers) treated conventionally at the 480 primary health care centres. The surgically treated patients obtain (variable) banding, vertical banded gastrop-lasty (VBG) or gastric bypass (3) (Figures 35.1-35.3).

SOS is a matched and not a randomized study since, in 1987, ethical approval for randomization was not obtained due to the high operative mortality (1-5%) observed in most surgical study groups from the 1970s and 1980s. Thus, partients choose for themselves if they want surgical or conventional treatment. When a surgical patient has been accepted according to a number of inclusion and exclusion criteria, a matching programme taking 18 different matching variables into account selects the optimal control among eligible individuals in the registry study (2). The selection is based on an algorithm moving the mean values of the matching

International Textbook of Obesity. Edited by Per Bjorntorp. © 2001 John Wiley & Sons, Ltd.

Figure 35.1 Gastric banding as originally described by Bo (59) and Solhaug (60). Later adjustable gastric banding was introduced (61-63). Copyright Sofia Karlsson and Lars Sjostrom

Figure 35.2 Vertical banded gastroplasty as described by Mason (64, 65). Copyright Sophia Karlsson and Lars Sjostrom variables of the control group towards the current mean values of the surgically treated patients. Thus a group match rather than an individual match is undertaken. The participating centres cannot influence the matching programme.

The surgically treated patient and the control start the intervention on the operation day of the former. Both patients are examined just before inclusion and then after 0.5,1,2,3,4,6,8 and 10 years. According to the original protocol the follow-up was planned to be 10 years for both groups, but recently, it was decided to add one 15- and one 20-year examination. Centralized biochemistry is obtained at 0, 2, 10, 15 and 20 years. All visits are automatically booked by a computer at the SOS secretariat and all centres obtain the necessary forms, test tubes etc. for a given visit some weeks before the booked appointment. If information is not coming back as expected from patients or centres, the programme is automatically sending out reminders or asks the staff of the secretariat to solve the problem by phone.

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