Erratum for Nakamura et al. Price promotions on healthier compared with less healthy foods: a hierarchical regression analysis of the impact on sales and social patterning of responses to promotions in Great Britain. Am J Clin Nutr 2015;101:808–16.
On the basis of feedback provided by a reader, we have identified several errors in this article. The errors all derive from our misinterpretation of a regression coefficient in our Supplemental Table 9. The correct interpretation is that a 10% increase in frequency of promotion (FoP) is associated with a 0.273% increase in total sales. This is an effect that is 1/100th of what we had originally reported.
Hence, in the Abstract, the third and fourth sentences of the Results section should read as follows: “However, after we controlled for the reference price, price discount rate, and brand-specific effects, the sales uplift arising from price promotions was larger in less-healthy than in healthier categories: a 1-SD point increase in the category mean NP score, implying the category becomes less healthy, was associated with an additional 0.077-percentage point increase in sales (from 0.273% to 0.350%; P < 0.01). The magnitude of the sales uplift from promotions was larger for higher socioeconomic status (SES) groups than for lower ones (0.346% for the high-SES group; 0.281% for the middle-SES group; and 0.231% for the low-SES group).”
On page 812, the first sentence of the second paragraph under the heading “Differential consumer responses to promotions by NP score” should read as follows: “A 10% increase in the frequency of promotions was associated with an increase in sales of 0.273% (95% CI: 0.206%, 0.339%; P < 0.01) for the whole population (average effect).” The third sentence in that paragraph should read as follows: “An SD point increase (6.96 points) in the category mean NP score (implying that the food category becomes less healthy) was associated with, all else being equal, an additional 0.077-percentage point increase in sales (P < 0.01; Supplemental Table 9) (i.e., the overall effect increased from 0.273% to 0.350%).”
In the third paragraph of that section, the third sentence should read as follows: “Moreover, SES differences in the sales uplift were more marked in healthier than in less-healthy food categories; for less-healthy food categories, the sales uplift for high-, middle-, and low-SES groups was 0.395%, 0.351%, and 0.315%, respectively, whereas in healthier food categories, it was 0.297%, 0.211%, and 0.147%, respectively.”
These errors also affect Figure 2. The numbers in the figure are now 1/100th of the previous ones (see revised Figure 2 below). The errors also affect the Online Supplemental Material. In the last paragraph on page 15, the first sentence should read as follows: “In the estimation using all households, an SD point increase in the category-level NP score (implying that the food category becomes less healthy) was associated with an additional 0.0766 (= 0.011 × 6.96) percentage point increase of the effect (P < 0.01).” Similarly, in Supplemental Figure 1, the numbers in the figure are now 1/100th of the previous ones. A corrected version of the Online Supplemental Material has been posted.
FIGURE 2.
