Skip to main content

Table 1 Results from four randomized controlled supermarket trials with different methods of adjustment for baseline covariates

From: Testing for baseline differences in randomized controlled trials: an unhealthy research behavior that is hard to eradicate

Study Comparisons Adjustment for covariates Outcome B Lower 95% CI Upper 95% CI p-value
1. Effects of 25% discounts on fruits and vegetables in a web-based supermarket [10] 25% discount on fruits and vegetables versus regular prices Adjusted for statistically significant characteristics only (= level of education) Fruit (g) 126 −376 630 0.62
Vegetables (g) 445 −105 995 0.11
F&V (g) 571 −300 1443 0.20
Fully adjusted (including for level of education) Fruit (g) 481 −69 1,030 0.09
Vegetables (g) 504 −64 1,071 0.08
F&V( g) 984 97 1,872 0.03
2. Introducing taxes, subsidies or both in a web-based supermarket [11] 25% discount on healthy foods versus no discount Adjusted for statistically significant characteristics only (= none) Fruit (g) −376 −1097 345 0.03*
Vegetables (g) 88 −678 854 0.01*
Fully adjusted Fruit (g) −382 −1105 341 0.10*
Vegetables (g) 52 −665 769 0.05*
50% discount on healthy foods versus no discount Adjusted for statistically significant characteristics only (= none) Fruit (g) 599 −126 1,323 0.03*
Vegetables (g) 1034 264 1,804 0.01*
Fully adjusted Fruit (g) 420 −322 1,163 0.10*
Vegetables (g) 821 85 1,556 0.05*
10% versus 5% increase on unhealthy foods Adjusted for statistically significant characteristics only (= none) Fruit (g) 216 −500 933 0.83*
Vegetables (g) −128 −889 633 0.45*
Fully adjusted Fruit (g) 304 −421 1,029 0.69*
Vegetables (g) 121 −598 840 0.59*
25% versus 5% increase on unhealthy foods Adjusted for statistically significant characteristics only (= none) Fruit (g) 82 −643 807 0.83*
Vegetables (g) 345 −425 1,115 0.45*
Fully adjusted Fruit (g) 83 −646 813 0.69*
Vegetables (g) 368 −355 1,091 0.59*
3. The effects of price discounts on fruits and vegetables with or without health education in a real supermarket [12] 50% discount on fruits and vegetables versus no intervention Adjusted for statistically significant characteristics only (= none) F&V(g) at 1 month 2386 87 4,685 0.04
F&V (g) at 3 months 1,226 −1,063 3,596 0.31
F&V (g) at 6 months 5,252 2,836 7,668 <0.01
F&V (g) at 9 months −826 −3,284 1,632 0.51
Fully adjusted F&V(g) at 1 month 1,295 −1,031 3,621 0.28
F&V (g) at 3 months 951 −1,293 3,194 0.41
F&V (g) at 6 months 3,894 1,500 6,287 <0.01
F&V (g) at 9 months −1,397 −3,833 1,038 0.26
Nutrition education versus no intervention Adjusted for statistically significant characteristics only (= none) F&V(g) at 1 month −1,583 −4,049 884 0.21
F&V (g) at 3 months −886 −3,432 1,661 0.50
F&V (g) at 6 months 35 −2,571 2,640 0.98
F&V (g) at 9 months −1,235 −3,747 1,277 0.34
Fully adjusted F&V(g) at 1 month −913 −3,383 1,557 0.47
F&V (g) at 3 months −91 −2,584 2,402 0.94
F&V (g) at 6 months 1,075 −1,468 3,617 0.41
F&V (g) at 9 months −481 −2,937 1,976 0.70
50% discount on fruits and vegetables + Nutrition education versus no intervention Adjusted for statistically significant characteristics only (= none) F&V(g) at 1 month 1,912 −354 4,179 0.10
F&V (g) at 3 months 978 −1,386 3,343 0.42
F&V (g) at 6 months 5,383 2,958 7,808 <0.01
F&V (g) at 9 months −1,176 −3,582 1,230 0.34
Fully adjusted F&V(g) at 1 month 1,290 −1008 3,587 0.27
F&V (g) at 3 months 1,213 −1,078 3,504 0.30
F&V (g) at 6 months 5,556 3,188 7,925 <0.01
F&V (g) at 9 months −1,157 −3,533 1,220 0.34
4. Effects of different discount levels on healthy products coupled with a healthy choice label in a web-based supermarket [13] 25% versus 10% discount on healthy foods Adjusted for statistically significant characteristics only (= none) Fruit (g) 398 −384 1,180 0.33*
Vegetables (g) −83 −887 721 <0.01*
Fully adjusted Fruit (g) 393 −442 1,228 0.52*
Vegetables (g) 39 −808 885 0.02*
50% versus 10% discount on healthy foods Adjusted for statistically significant characteristics only (= none) Fruit (g) 544 −193 1,280 0.33*
Vegetables (g) 1,108 350 1866 <0.01*
Fully adjusted Fruit (g) 410 −361 1,182 0.52*
Vegetables (g) 1,017 226 1,807 0.02*
Special offer label versus combined label Adjusted for statistically significant characteristics only (= none) Fruit (g) 61 −676 797 0.94*
Vegetables (g) −436 −1,193 322 0.52*
Fully adjusted Fruit (g) 74 −704 853 0.78*
Vegetables (g) −479 −1,286 328 0.50*
Healthy choice label versus combined label Adjusted for statistically significant characteristics only (= none) Fruit (g) −76 −858 705 0.94*
Vegetables (g) −217 −1,021 587 0.52*
Fully adjusted Fruit (g) −200 −1,014 613 0.78*
Vegetables (g) −282 −1,138 574 0.50*
  1. *Overall p-value comparing the three groups.
  2. CI = confidence interval; F&V = fruit and vegetables.