Randomized Controlled Trial

A - Click here for explanation of classification scheme.

POSITIVE: See Quality Criteria Checklist below.

• To test the effectiveness of a weight-loss intervention that used loss aversion (the tendency for people to put substantially greater weight on losses than gains) to magnify the impact of incentives
• In this financial incentive study, participants voluntarily enter into a pre-commitment or deposit contract, in which their own money is put at risk such that they lose money if they are unsuccessful in losing weight.

• Patients identified through a Philadelphia Veterans Affairs Medical Center (PVAMC) patient database
• Must have been between ages 30 years to 70 years and between body mass index (BMI) of 30kg/m² to 40kg/m².

If the investigators considered participation either infeasible (e.g., illiteracy) or unsafe (e.g., serious psychiatric diagnoses).

Recruitment

• Participants meeting initial eligibility requirements were identified through a Philadelphia Veterans Affairs Medical Center (PVAMC) patient database
• A randomly selected subset was recruited using mailings; those interested were screened for eligibility.

Design

• A 32-week, three-arm randomized controlled trial
• A 24-week weight-loss phase during which all participants were given a weight loss goal of one pound per week, followed by an eight-week maintenance phase in which participants were not required to lose weight. This was included to assess the impact of framing this period as maintenance vs. an ongoing opportunity for continued weight loss
• To assess longer-term maintenance following the 32-week intervention, participants returned for a weigh-in approximately 36 weeks after the last participant had completed the 32-week intervention.

Intervention

• Participants were randomized evenly to one of three groups:
  • Weight-monitoring program (control condition) or
  • The same program with one of two financial incentive plans (deposit contract conditions or DC1 and DC2):
    • DC1: The first 24 weeks of the study were described as the weight-loss period; the final 8 weeks (i.e., weeks 25 to 32) were framed as the maintenance of weight-loss period
    • DC2: Basically the same except that there was no explicit distinction between the two periods of the study, which was also the case in the control condition.
  • Groups used a block size of six, with stratification based on sex and age (30 years to 49 years vs. 50 years to 70 years).
• Control group:
  • One-hour, one-on-one consultation with a dietitian at enrollment:
    • Strategies for weight loss were discussed, along with goal setting and monthly weigh-ins
    • Weight loss target of 24 pounds in the first 24 weeks
    • In the second phase, participants who attained the 24-pound weight-loss goal could choose a goal of zero, 0.5, or one pound per week for weeks 25 to 32 of the study
    • Participants received a scale to monitor their weight at home daily
    • At the end of each month, participants received $20 for returning to the clinic to be weighed.
• DC groups:
  • Subjects were given a chart at the initial visit depicting the daily weight goals to attain to qualify for incentives and a handout describing the incentive plan
    • At the beginning of each month, they could contribute between zero and $3 per day of their own funds to a deposit contract
    • During the month, participants accumulated rewards. For each day that a participant called in and reported a weight at or below his weight loss goal, he accumulated a reward equal to his daily deposit, plus a 1:1 match from the study.
    • Participants would only receive accumulated awards if they weighed at or below their weight loss goal at the end of the month weigh-in
    • Participants could earn $84 net ($168 gross) per month (i.e., by making the maximum $3 daily deposit, and on every day of the month, truthfully reporting that they had attained their daily weight loss goal).
  • Participants were instructed to (assumed by a dietitian, although unclear):
    • Weigh themselves each morning before eating or drinking and after urinating
    • Record their weights
    • Call in their weight by noon.
  • They received daily text messages indicating whether they were on track toward attaining their monthly weight loss goal and how much they had earned that day in incentives
  • Non-adherent participants received feedback about what they would have earned had they met their target weight
  • Deposit contract money that was forfeited by participants failing to lose sufficient weight was contributed to a pool of money divided equally among DC participants who lost 20 pounds or more by the end of 24 weeks
  • The weight loss trajectory was reset at monthly intervals for those failing to attain goals
  • For those who had surpassed their goals, the trajectory was flattened; those individuals could then lose weight at a slower rate and still attain the final 24-pound weight loss goal
  • Participants above their goal at the end of a month were given a fresh start in which the overall goal was unchanged, but the slope of the trajectory was adjusted (i.e., steepened) such that the participant need not binge diet to resume receiving incentive payments.

Statistical Analysis

• Power calculations were based on detecting clinically significant weight loss: Weight loss of 11 pounds (5kg) at 32 weeks
• Making the assumption of an 11-pound standard deviation for weight loss and using a two-sided alpha of 0.025, the study required 22 participants per arm to provide 90% power to detect clinically significant differences between groups
• Pearson’s X² test or Fisher’s exact test was used for categorical variables, as appropriate
• T-tests or Wilcoxon rank sum was used for continuous variables, as appropriate
• All tests were two-sided.

Timing of Measurements

• A 32-week study
• DC participants weighed each morning at home
• Both control and DC group participants weighed and at the end of each month at the clinic office
• Participants weighed again at the end of 36 weeks to check weight loss maintenance after the intervention ended.

Dependent Variables

• Weight:
  • DC participants were given a scale to weigh at home. They weighed each morning after urinating and before eating or drinking at home.
  • DC participants and control participants weighed and at the end of each month at the clinic office
  • Participants weighed again at the end of 36 weeks to check weight-loss maintenance after the intervention ended.
• Finances:
  • Control participants received $20 for returning to the clinic to weigh at the end of the month
  • DC1 participants and DC2 participants could earn $84 net ($168 gross) per month (i.e., by making the maximum $3 daily deposit, and on every day of the month, truthfully reporting that they had attained their daily weight loss goal).

Independent Variables

Group assignment into control group, DC1 or DC2.

Control Variables

To control for variation in weighing, the DC participants were given the same type of scale to use at home to weigh daily.

Initial N

N=66 participants (22 in each group): 

• Control Group: 18 males, four females
• DC1 Group: 18 males, four females
• DC2 Group: 19 males, three females.

Attrition (Final N)

At the primary outcome point, 10% lost to follow-up (C lost one of 22, DC1 lost one of 22, DC2 lost four of 22).

• Control Group: N=21
• DC1: N=21
• DC2: N=18.

Age

Between 30 years and 70 years, otherwise not described.

Ethnicity

	Control (N=22)	DC1 (N=22)	DC2 (N=22)
Black	9 (40.1)	14 (63.6)	13 (59.1)
White	10 (45.5)	7 (31.8)	9 (40.9)
Hispanic	2 (9.1)	0	0
American Indian or Alaskan Native	1 (4.5)	0	0

Other Relevant Demographics
 

	Control (N=22)	DC1 (N=22)	DC2 (N=22)
Married	17 (77.3)	10 (45.5)	11 (52.4)
Education
Some high school	2 (9.1)	0	3 (13.6)
Completed high school or GED	8 (36.4)	8 (38.1)	8 (36.4)
Some college or higher	12 (54.5)	13 (59.0)	11 (50.0)
Median total annual household income	$48,500	$32,500	$35,550
Self-rated health measured on a one-to-five scale, endpoints labeled "poor" and "excellent"* (SD)	3.05 (0.90)	3.68 (0.95)	3.00 (0.93)
Self-rated importance of controlling weight* (SD)	9.05 (1.39)	9.56 (0.92)	7.67 (2.34)
Confidence in ability to lose weight (SD)	8.37 (1.89)	8.39 (2.57)	8.00 (1.64)
Physical health co-morbidities
Shortness of breath at rest	1 (4.5)	5 (22.7)	1 (4.5)
Chest pains not evaluated by physician	0	1 (4.5)	0
Active infection	0	9.1 (2)	0
Hernia in groin or belly area	2 (9.1)	2 (9.1)	2 (9.1)
Retinal hemorrhage	0	0	0
Loss of balance	0	1 (4.5)	2 (22.7)
Chronic medical problem flare-up	2 (9.1)	4 (18.2)	6 (27.3)
Back pain or spinal disc disease	9 (40.9)	11 (50.0)	63.6 (14)
Osteoporosis or bone disease	3 (13.6)	3 (13.6)	1 (4.5)
Amputation	0	0	0
Spinal cord injury	0	0	9.1 (2)
Lung disease	4 (18.2)	4 (18.2)	1 (4.5)
Heart disease	2 (9.1)	2 (9.1)	6 (27.3)
Poor circulation	1 (4.5)	1 (4.5)	4 (18.2)
Stroke, TIA or carotid surgery in neck	1 (4.5)	0	0
Diabetes	1 (4.5)	3 (13.6)	4 (18.2)
High blood pressure	15 (68.2)	12 (54.5)	14 (63.6)
High blood cholesterol	13 (59.1)	6 (27.3)	10 (45.5)
Family member with heart problems at age younger than 50 years	3 (13.6)	2 (9.1)	2 (9.1)
Psychological or chemical co-morbidities
Too much stress	6 (27.3)	5 (22.7)	8 (36.4)
General unhappiness	4 (18.2)	5 (22.7)	4 (18.2)
Depression	7 (31.8)	6 (27.3)	9 (40.9)
Anxiety problems	6 (27.3)	5 (22.7)	4 (18.2)
Family or relationship problems	7 (31.8)	6 (27.3)	4 (18.2)
Bipolar disorder	0	1 (4.5)	1 (4.5)
Schizophrenia	0	0	0
Post-traumatic stress disorder	11 (50)	7 (31.8)	8 (36.4)
Obsessive compulsive disorder	0	2 (9.1)	0
Eating disorder	1 (4.5)	1 (4.5)	2 (9.1)
Tobacco use	3 (13.6)	7 (31.8)	1 (4.5)
Substance abuse or dependence	0	1 (4.5)	0

Baseline characteristics of the three groups were generally equivalent, with the exception of three variables:

• Importance of controlling weight [F(2,66) = 3.84, P=0.03]:
  • Control: 9.05
  • DC1: 9.56
  • DC2: 7.67.
• Proportion using tobacco [X²(2) = 6.11, P=0.05]:
  • Control: 13.6%
  • DC1: 31.8%
  • DC2: 4.5%
• Self-rated health (P=0.03):
  • Control: 3.1 of five
  • DC1: 3.7 of five
  • DC2: of 3.0 of five.
• There were differences in marital status and household income that were possibly clinically, though not statistically, significant.

Anthropometrics

	Control (N=22)	DC1 (N=22)	DC2 (N=22)
Height (SD)	5'8" (3.0")	5'7" (2.9")	5'7" (3.4")
Initial weight measurement in pounds (SD)	230.9 (23.9)	227.7 (23.3)	231.2 (31.9)
BMI (SD)	34.7 (3.2)	35.1 (2.4)	34.1 (2.8)

Location

Philadelphia.
 

Key Findings

	Control (N=22)	DC1 (N=22)	DC2 (N=22)
Total weight loss, pounds
Mean (SD)	1.2 (13.8)	9.6 (13.6)	7.6 (12.8)
95% CI	5.0 (gain) to 7.3	3.6 to 15.7	2.1 to 13.4
Met 24-pound weight loss goal by week 32
Number (%)	2 (9.1)	4 (18.2)	2 (9.1)
95% binomial CI	1.1 to 29.2	5.2 to 40.3	1.1 to 29.2

 
Other Findings

• Mean weight loss at 32 weeks was not statistically different between the two incentive arms (mean DC1 of 9.65 pounds, SD=13.62; mean DC2 of 7.75 pounds, SD=12.82; F(one, 41)=0.064, P=0.80] so the incentive conditions were pooled together for analyses
• Mean weight loss at 32 weeks was statistically greater in the incentive groups (DC=8.70 pounds) relative to the control arm (C=1.17 pounds) [T(64)=2.16, P=0.04, 95% CI of the difference in means (0.56, 14.50)]
• At 24 weeks (the end of the weight loss phase of the study) 10.6% of participants had attained the goal of losing 24 pounds; this rate was not different between conditions [mean C=9.1% (two of 22), mean DC=11.4% (five of 44), X²(1)=0.080, P=0.78]
• The proportion of participants who had attained and maintained a 24-pound weight loss at 32 weeks was low and similar across arms [mean C=9.1% (two of 22), mean DC=13.6% (six of 44), !2(1)=0.284, P=0.59]
• Participants in the DC groups who had lost at least 20 pounds by the end of 32 weeks each received $467.80 (their share of the money forfeited by participants in the DC arms who did not attain their goals)
• Since very few participants (seven of 66) attained the initial weight loss goal, they were not able to examine with any statistical precision how participants did, given their secondary goals during the maintenance phase
• Although the proportion of participants contributing to deposit contracts decreased over time (58.1% in month eight), most participants made a deposit every month (mean number of months in which a deposit was made was 6.0, with SD of 2.7 and median of 7.0)
• Among participants not lost to follow-up, the average daily deposit contract contribution was $0.85 (SD=0.81); the median was $0.67 (IQR=0.83) and did not differ between incentive arms
• When participants lost to follow-up are included, the average daily deposit contract contribution was $0.77 (SD=0.79); the median was $0.63 (IQR=0.80)
• The average net incentive earnings was $88.18 (SD=117.64); the amount did not differ between DC groups
• Of those who completed the study, the daily call-in rate was extremely high and the same between incentive conditions (99.9%)
• Sixty-five percent of participants [43 of 66; control with 14 of 22, DC with 29 of 44; X²(1) =0.86, P=0.86] returned to the clinic for a follow-up weigh-in approximately 36 weeks after the last participant had completed the 32-week intervention (as with the primary endpoint, participants lost to follow-up were assumed to have reverted to baseline weight)
• There was substantial weight regain, particularly in the incentive conditions [mean DC was 7.5 pounds (95% CI: 4.12 to 10.95); mean C was 0.90 pounds (95% CI: -4.86 to 6.67); T=2.14, P=0.04).

• Incentive approaches based on behavioral economics are effective in inducing weight loss over an eight-month intervention period
• Future research is needed to devise techniques that promote sustained weight loss over longer periods of time.

Government:	USDA economic research service grant
Other:	Hewlett Foundation

• There were several variables assessed for this group but gambling was not one of them. For any kind of financial incentive or reward type of program, shouldn't gambling addiction be assessed?
• Unclear if the DC groups also were seen by a RD.