A Natural Experiment Evaluating the Effect of a Minimum Wage Increase on Obesity and Diet-related Outcomes

Study Overview
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Brief Summary
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To evaluate the effect of the Minneapolis minimum wage ordinance on change in body mass index among low-wage workers.

Detailed Description
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On June 30 2017, Minneapolis became the 40th local jurisdiction to set the minimum wage above the state level, following a succession of other cities and counties across the U.S that have passed similar ordinances since 2012. The city of Minneapolis will incrementally increase the minimum wage from $9.50 to $15 by July 1, 2022 for all businesses with greater than 100 employees; minimum wage in smaller businesses will increase from $7.75 to $13.50 during this same time period. The ordinance specifically states that its purpose is to maintain worker's health, efficacy, and general well-being. A report by members of the study team at the Humphrey School of Public Affairs at University of Minnesota estimates that the ordinance would increase wages by an average of 22% for the 71,000 city workers making minimum wage or just above minimum wage; moreover, it would affect 41% of non-Hispanic black workers and 54% of Hispanic workers, compared with 17% of white workers. The report also projects a post-policy decrease in food insecurity of 3.8 percentage points and an increase in food expenditures of $26 per week among affected workers. The available evidence suggests that minimum wage laws may be associated with a range of health outcomes, including obesity. Obesity affects 36.5% of Americans, and is disproportionately high among non-Hispanic blacks and Hispanics. A study by Meltzer and Chen (2009) estimated that 10% of the increase in body mass in the U.S. since 1970 can be explained through the diminished value of minimum wages by inflation, while Kim & Leigh (2010) used instrumental variables to demonstrate that low wages increase the risk of obesity. Mechanisms through which increasing the minimum wage could reduce obesity include improving food security and reducing cost constraints for purchasing healthier foods. However, existing studies linking wages and weight have design weaknesses that limit causal inference and the ability to identify causal mechanisms. A prospective study with a strong counterfactual condition is needed to test whether and how an increase in minimum wage results in improved obesity-related outcomes among low-wage workers. Throughout the 4.5-year implementation period of the Minneapolis minimum wage ordinance (January 1, 2018-July 1, 2022), the team will follow a cohort of low-wage workers in a natural experiment, using a difference-in-difference design to compare a panel of obesity-related measures among low-wage workers (those earning ≤$10 an hour at baseline) in Minneapolis (n = 400) with low-wage workers in a comparison city with no minimum wage increase (Raleigh, North Carolina, n = 400).

Official Title
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A Natural Experiment Evaluating the Effect of a Minimum Wage Increase on Obesity and Diet-related Outcomes

Conditions
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Obesity, Nutrition Poor

Intervention / Treatment
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* Other: Increase Minimum Wage to $15-an-hour
* Other: No Increase in Minimum Wage


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Age 18 or older. Plan to serve in the workforce for at least 5 years Have an address and phone number where they can receive mail and phone calls (though they do not necessarily need to own a phone or have a permanent home) Speak English or Spanish well enough to complete the survey Either A OR B must be true: A: Work at a wage of $11.50 an hour for at least an average of 10 hours a week, with at least 2 of those hours at a job in Minneapolis B: Be currently unemployed, but worked at a wage of $11.50 an hour or less for at least an average of 10 hours a week in the last 6 months AND be currently looking for working in Minneapolis Exclusion Criteria: Federal or state workers Full-time students Plan to retire or move more than 100 miles away in the next 5 years

Ages Eligible for Study
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Minimum Age: 18 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Low-Wage Workers from Minneapolis, MN<br>Low-wage workers from Minneapolis, MN, where the minimum wage will be increased to $15-an-hour over the study period. | Other: Increase Minimum Wage to $15-an-hour<br>* Increase in minimum wage to $15-an-hour<br>|
| Low-Wage Workers from Raleigh, NC<br>Low-wage workers from Raleigh, NC, where the minimum wage will not be significantly changed over the study period. | Other: No Increase in Minimum Wage<br>* No increase in minimum wage<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Change in Body Mass Index | Body mass index (BMI) will be measured over 5 years among low-wage workers in Minneapolis compared to workers in a comparison (control) city, as assessed by objective annual height and weight measurements. | 5 years | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Change Purchase of Healthier Foods | Change in purchasing of healthier foods (e.g. fruits and vegetables) and less healthy foods (e.g. sugar sweetened beverages) will be measured by 2 weeks of food purchase receipts, among a cohort of low-wage workers in Minneapolis compared to a control city. | 5 years | 
| Change in Food Insecurity | Change in food insecurity will be measured by the U.S. Household Food Security Survey Module: Six-Item Short Form (from the Economic Research Service, USDA September 2012), among a cohort of low-wage workers in Minneapolis compared to a control city. Scores are calculated by simple addition for the 6 items. Scores range from 0 (high food security) to 6 (very low food security). | 5 years | 
| Change in Food Assistance Program Participation | Change in participation in government-supported food assistance program (SNAP, WIC, FRPL) will be measured by self report among a cohort of low-wage workers in Minneapolis compared to a control city. | 5 years | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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obesity, overweight, food insecurity, food assistance program, minimum wage