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Table 4 Statistical test outcomes and interpretation for energy and nutrient intakes derived from the test data set 1

From: Application and interpretation of multiple statistical tests to evaluate validity of dietary intake assessment methods

Nutrient Spearman correlation (r value) Wilcoxon signed rank test (P value) Percentage difference (%) Cross-classification (Tertiles) Weighted Kappa statistics (value) Bland – Altman 2,3 Spearman Correlation (r value)
  Association (strength & direction) Agreement Agreement (size & direction of error) Agreement (including chance) Agreement (excluding chance) Presence, direction and extent of bias
  % in same tertile % in opposite tertile
Level of validation Individual Group Group Individual Individual Individual Group
Energy (kJ) 0.26 P > 0.05 −9.8 46.8 19.2 0.20 P < 0.001
Validly interpretation Acceptable Good Good Poor Poor Acceptable Biased
Protein (g) 0.23 P < 0.01 −19.1 42.6 23.4 0.12 P < 0.05
Validly interpretation Acceptable Poor Acceptable Poor Poor Poor Biased
Fat (g) 0.01 P > 0.05 −6.9 34.0 31.9 −0.01 P > 0.05
Validly interpretation Poor Good Good Poor Poor Poor Not biased
Carbohydrates (g) 0.40 P > 0.05 −1.4 50.0 17.4 0.25 P < 0.01
Validly interpretation Acceptable Good Good Good Poor Acceptable Biased
Folate (mcg) 0.40 P < 0.05 33.0 53.2 8.5 0.30 P < 0.01
Validly interpretation Acceptable Poor Poor Good Good Acceptable Biased
Vitamin A (mcg) 0.15 P < 0.01 −22.9 34.0 14.9 0.03 P > 0.05
Validly interpretation Poor Poor Poor Poor Poor Poor Not biased
Iron (mg) 0.38 P > 0.05 −24.8 51.1 23.4 0.29 P < 0.01
Validly interpretation Acceptable Good Poor Good Poor Acceptable Biased
  1. 1Energy and nutrient intake derived from a QFFQ and four repeated 24-hour recalls conducted in 18–65 year old adults (n = 47, 11 males & 36 females) in a rural area in the Eastern Cape.
  2. 2% in LOA: Energy: 93.6%; protein: 95.7%, fat: 97.9%, carbohydrate: 95.7%; folate: 95.7%, vitamin A: 89.4%; iron: 98%.
  3. 3Upper & lower limits of agreement (LOA) and DRI for females aged 18 to 55: energy (kJ): −13406 & 10694 (EER: 10093 kJ); protein (g): −94.6 & 59.4 (RDA: 46 g); fat: −125.4 & 96.6 (no DRI); folate (mcg): −649 & 925.8 (RDA: 400mcg); vitamin A (mcg): −876 &576.4 (RDA: 700mcg); iron (mg): −22,4 &10.4 (RDA: ????mg).
  4. Interpretation criteria for statistical tests.
  5. Wilcoxon signed rank test: Good: p > 0.05; Poor: ≤ 0.05 [9].
  6. Percentage difference: Good: 0.0 – 10.9%; Acceptable: 11.0 – 20.0%; Poor: > 20.0% [92].
  7. Correlations coefficient (Spearman): Good: ≥ 0.50; Acceptable: 0.20 – 0.49; Poor < 0.20[2]
  8. Cross-classification (Tertiles) (% in same tertile): Good: ≥ 50%; Poor: < 50% [2].
  9. Cross-classification (% in opposite tertile): Good: ≤ 10%, Poor: > 10% [2].
  10. Weighted Kappa statistics: Good: ≥ 0.61; Acceptable: 0.20 – 0.59; Poor: < 0.20 [2].
  11. Bland-Altman - Correlation coefficient (Spearman): Good: P > 0.05; Poor: P ≤ 0.05 [2].