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Table 3 Changes in the prevalence of households purchasing beverages in Tonga from 2009 to 2015/16

From: Equity of expenditure changes associated with a sweetened-beverage tax in Tonga: repeated cross-sectional household surveys

Characteristic   Purchasing prevalence (% households)
2009 2015/16 Absolute difference Relative change (%) Diff. p-value
Soft drinks (taxed in 2013) Total All 51.3 (48.3 to 54.3) 40.4 (37.3 to 43.5) −10.9 (−15.2 to −6.5) −21.2 (−28.7 to − 13.4) < 0.001
Age Adults only 45.8 (41.3 to 50.4) 34.4 (28.2 to 40.6) −11.4 (−19.1 to −3.7) −24.9 (−40.1 to −9.0) 0.004
Adults and children 53.2 (49.7 to 56.7) 42.8 (39.1 to 46.4) −10.5 (−15.5 to −5.4) −19.6 (−28.1 to − 10.8) < 0.001
  p-value    0.835   
Income tertile Lowest 46.9 (42.0 to 51.7) 32.6 (27.2 to 38.0) −14.3 (−21.5 to −7.0) −30.4 (−43.6 to − 16.5) < 0.001
Middle 51.0 (46.8 to 55.1) 45.5 (40.7 to 50.2) −5.5 (−11.9 to 0.8) − 10.8 (−22.4 to 1.3) 0.087
Highest 56.0 (51.6 to 60.3) 41.8 (37.1 to 46.5) −14.1 (−20.6 to −7.7) −25.3 (−35.3 to − 14.8) < 0.001
  p-value    0.980   
Island Outer islands 35.1 (30.7 to 39.5) 23.1 (18.5 to 27.7) −12.0 (−18.3 to −5.6) −34.1 (−49.1 to − 18.0) < 0.001
Tongatapu (main island) 58.6 (54.7 to 62.4) 47.2 (43.3 to 51.2) −11.3 (−16.9 to −5.8) −19.4 (−27.8 to −10.6) < 0.001
  p-value    0.886   
Milk Total All 29.9 (27.3 to 32.4) 44.5 (40.7 to 48.4) 14.6 (10.0 to 19.3) 49.0 (31.3 to 67.8) < 0.001
Age Adults only 26.3 (22.1 to 30.4) 39.7 (33.8 to 45.7) 13.4 (6.2 to 20.7) 51.2 (19.9 to 86.4) < 0.001
Adults and children 31.1 (28.0 to 34.3) 46.4 (42.1 to 50.7) 15.2 (9.9 to 20.5) 48.9 (29.3 to 70.0) < 0.001
  p-value    0.698   
Income tertile Lowest 22.9 (19.5 to 26.3) 36.2 (30.6 to 41.9) 13.3 (6.7 to 19.9) 58.0 (25.7 to 93.9) < 0.001
Middle 30.9 (26.7 to 35.1) 46.0 (40.5 to 51.4) 15.0 (8.2 to 21.9) 48.6 (23.2 to 76.9) < 0.001
Highest 35.8 (32.1 to 39.5) 49.6 (43.4 to 55.8) 13.8 (6.6 to 21.1) 38.7 (16.9 to 62.1) < 0.001
  p-value    0.913   
Island Outer islands 18.8 (15.1 to 22.5) 27.3 (23.2 to 31.3) 8.5 (2.9 to 14.0) 44.9 (11.5 to 84.2) 0.003
Tongatapu (main island) 34.8 (31.5 to 38.2) 51.3 (46.3 to 56.3) 16.4 (10.4 to 22.5) 47.2 (27.7 to 68.1) < 0.001
  p-value    0.055   
Bottled water Total All 10.4 (8.7 to 12.1) 35.0 (31.5 to 38.4) 24.6 (20.7 to 28.4) 236.5 (176.3 to 306.0) < 0.001
Age Adults only 9.4 (6.8 to 12.0) 31.9 (25.5 to 38.2) 22.5 (15.7 to 29.4) 240 (135 to 375) < 0.001
Adults and children 10.8 (8.7 to 12.8) 36.2 (32.6 to 39.8) 25.4 (21.3 to 29.5) 236 (169 to 316) < 0.001
  p-value    0.477   
Income tertile Lowest 6.2 (4.1 to 8.3) 28.4 (23.5 to 33.2) 22.1 (16.8 to 27.4) 355 (203 to 563) < 0.001
  Middle 9.7 (6.7 to 12.6) 33.5 (28.5 to 38.5) 23.8 (18.0 to 29.6) 246 (141 to 385) < 0.001
  Highest 15.3 (12.1 to 18.4) 41.5 (36.1 to 47.0) 26.3 (20.0 to 32.6) 172 (111 to 246) < 0.001
  p-value    0.324   
Island Outer islands 2.0 (1.0 to 3.1) 19.3 (15.6 to 23.0) 17.2 (13.4 to 21.1) 849 (399 to 1606) < 0.001
Tongatapu (main island) 14.2 (11.7 to 16.6) 41.2 (36.7 to 45.7) 27.0 (21.9 to 32.1) 191 (136 to 255) < 0.001
  p-value    0.003   
  1. All values are survey weighted to be representative of the national Tongan population. Absolute differences were calculated from the difference between the two means, with t-tests used to give the 95% confidence interval (CI) for the absolute difference and the p-value. Percentage change confidence intervals were calculated using the Fieller method [29]. The absolute difference p-value tests the null hypothesis that the absolute changes in outcome were the same in each sub-group, for example comparing the highest and lowest income group. The difference (Diff.) p-value tests for whether there was any evidence against the null hypothesis that there was no change over time between the two surveys. Source: Tonga Department of Statistics