The Academy will be conducting system maintenance beginning at 7:00 p.m. (Eastern Time) on September 25. This maintenance period will continue for 24 to 48 hours. During this time, EAL content which requires member login, as well as the purchase of new subscriptions, will be unavailable. We apologize for the inconvenience.

MNT: Weight Management (2015)

Citation:

John LK, Loewenstein G, Troxel AB, Norton L, Fassbender JE, Volpp KG. Financial incentives for extended weight loss: A randomized controlled trial. J Gen Intern Med. 2011 Jun; 26(6): 621-626.
 

PubMed ID: 21249462
 
Study Design:
Randomized Controlled Trial
Class:
A - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
  • 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.
Inclusion Criteria:
  • 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.
Exclusion Criteria:
If the investigators considered participation either infeasible (e.g., illiteracy) or unsafe (e.g., serious psychiatric diagnoses).
Description of Study Protocol:

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.
Data Collection Summary:

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.

Description of Actual Data Sample:
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.
 

Summary of Results:

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).
Author Conclusion:
  • 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.
Funding Source:
Government: USDA economic research service grant
Other: Hewlett Foundation
Reviewer Comments:
  • 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.
Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
 
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? No
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? N/A
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? ???
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? No
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? Yes
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? N/A
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? No
  6.6. Were extra or unplanned treatments described? No
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? ???
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? No
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? No
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? No
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes