GB794 Unit 9 Evidence Summary Example

Stars on the Shelf: A Unit 9 Evidence Summary on Supermarket Nutrition Rating Systems

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Purdue University Global

GB794: Advanced Topics in Marketing

Unit 9 Evidence Summary

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[Date]

Thornbury Market is composite and illustrative; the five studies summarized are real.

The Decision Behind the Review

Thornbury's merchandising team has proposed adding a nutrition rating to shelf tags across its stores, using a published algorithm that awards zero to three stars based on nutrients. The team expects the ratings to move shoppers toward more nutritious items and, possibly, to raise sales by attracting health-conscious shoppers. This summary examines what published evidence says about both expectations.

The Five Studies

Sutherland et al. (2010). This study examined the introduction of the Guiding Stars system at Hannaford supermarkets in the northeastern United States, comparing purchases of rated foods before and after the system was introduced. It reported that purchases shifted toward items carrying stars in several categories, including ready-to-eat cereals. It compared one chain's purchases before and after launch, with no outside comparison.

Rahkovsky et al. (2013). Using scanner data on ready-to-eat cereal purchases in the chain's stores, this study estimated how demand for cereals with different ratings changed after the same system was introduced. It found that the program increased demand for more nutritious cereals and decreased demand for less nutritious ones, with effects that were statistically significant but modest in size.

Cawley et al. (2015). This study analyzed weekly sales for 102 food categories across 168 supermarkets of a chain in the northeastern United States from 2005 to 2007, controlling for seasonality and time trends. After the ratings were introduced, overall weekly food sales declined by about 3,637 units per category. Sales of less nutritious foods fell by about 8 percent, while sales of nutritious foods did not change significantly. As a result, the share of purchases rated nutritious rose by about 1.4 percentage points.

Hobin et al. (2017). Studying the introduction of the Guiding Stars system in a Canadian supermarket chain, this study compared stores that adopted the system with stores that did not. It found shifts in purchasing toward rated items that translated into measurable nutritional improvements, such as slightly less sugar and trans fat and more fiber, and reported a positive effect on sales and revenue, which the authors emphasized because retailers are more likely to sustain programs that pay.

Sacks et al. (2009). This study examined front-of-pack traffic-light labels, which display red, amber or green for several nutrients, introduced by a major British retailer in 2007. Comparing sales of selected ready meals and sandwiches in the four weeks before and after labeling, it found that ready-meal sales rose while sandwich sales did not change, and that changes in sales were unrelated to how healthy the products were.

Three Claims, Graded

Claim 1: Shelf rating systems shift purchases modestly toward rated-nutritious items. Supported. Four of the five studies, using different chains, countries and analytic methods, found shifts in this direction, while the fifth, on a different label format applied to only two categories, found none. The shifts were small, typically a percentage point or two in the share of purchases rated nutritious, and none of the studies randomized which stores received the ratings.

Claim 2: The shift comes more from reduced purchases of less nutritious items than from increased purchases of nutritious ones. Suggestive. Cawley and colleagues found this pattern directly. Rahkovsky and colleagues found movement in both directions. The other studies did not separate the two. The evidence is consistent but rests mainly on one study.

Claim 3: Rating systems raise a grocer's total sales. Contested. Hobin and colleagues reported higher sales and revenue after adoption. Cawley and colleagues reported lower total unit sales. The difference may reflect the chains, the period, the measures or the comparison designs, and two studies pointing in opposite directions cannot settle the question.

The evidence is firmest that star ratings nudge shoppers a little toward healthier items, and weakest on the question a retailer cares most about, whether the stars pay.

What the Set Cannot Say

Three limits apply across the studies. First, none randomized the introduction of ratings, so each relied on before-and-after comparisons or comparison stores that may differ from the stores that adopted ratings. Second, most studies examined one rating system, Guiding Stars, in mainstream supermarkets, and some were conducted with the involvement of the system's developers or the adopting retailer, which a reader should note. Third, the studies measured purchases, not consumption or health.

Reading the Studies Together

Reading the five side by side brings out three patterns. First, effects were larger in categories where products differ widely on nutrition and look similar on the shelf, such as cereals, where a rating adds information a shopper could not easily see. They were smaller or absent in categories like sandwiches, where shoppers may choose on taste or convenience. Second, the studies that found the largest shifts examined systems introduced across whole stores with promotion, while the one null result examined labels on a narrow range of products over four weeks. Third, the studies differ in what they counted: units, revenue, share of purchases or nutrient content. A reader comparing their headline figures without noting those differences would draw false conclusions about which systems work best.

These patterns suggest that the effect of ratings depends on the category and the scale of introduction, which matters for Thornbury, since a rollout limited to a few categories would be expected to show smaller effects than a store-wide program.

How Far the Claims Reach Thornbury

Thornbury is a natural-foods grocer whose shoppers already buy more products that a rating algorithm would score well. Two consequences follow. The room for shifting purchases toward rated items is likely smaller than in a mainstream chain, since more of what shoppers buy already earns stars. And the sales question may run differently: if many items in a natural-foods store earn stars, the ratings differentiate less, and if some popular items do not, shoppers may be surprised. The evidence supports expecting, at most, a small shift in purchases and gives no reliable guidance on sales.

Recommendation

Thornbury should not adopt ratings chain-wide on the expectation of higher sales. If it adopts them for their informational value to shoppers, it should introduce them in a randomly chosen half of its stores first, so that their effect on purchases and sales can be measured directly, an improvement on the designs in all five studies. Measuring both purchases and total store sales in that test would answer the two questions the published evidence leaves furthest apart.

References

Cawley, J., Sweeney, M. J., Sobal, J., Just, D. R., Kaiser, H. M., Schulze, W. D., Wethington, E., & Wansink, B. (2015). The impact of a supermarket nutrition rating system on purchases of nutritious and less nutritious foods. Public Health Nutrition, 18(1), 8-14. https://doi.org/10.1017/S1368980014001529

Hobin, E., Bollinger, B., Sacco, J., Liebman, E., Vanderlee, L., Zuo, F., Rosella, L., L'Abbe, M., Manson, H., & Hammond, D. (2017). Consumers' response to an on-shelf nutrition labelling system in supermarkets: Evidence to inform policy and practice. The Milbank Quarterly, 95(3), 494-534. https://doi.org/10.1111/1468-0009.12277

Rahkovsky, I., Lin, B.-H., Lin, C.-T. J., & Lee, J.-Y. (2013). Effects of the Guiding Stars Program on purchases of ready-to-eat cereals with different nutritional attributes. Food Policy, 43, 100-107. https://doi.org/10.1016/j.foodpol.2013.08.013

Sacks, G., Rayner, M., & Swinburn, B. (2009). Impact of front-of-pack "traffic-light" nutrition labelling on consumer food purchases in the UK. Health Promotion International, 24(4), 344-352. https://doi.org/10.1093/heapro/dap032

Sutherland, L. A., Kaley, L. A., & Fischer, L. (2010). Guiding Stars: The effect of a nutrition navigation program on consumer purchases at the supermarket. The American Journal of Clinical Nutrition, 91(4), 1090S-1094S. https://doi.org/10.3945/ajcn.2010.28450C