TABLE 2.
Information on the best-fit regression model between previous and newly measured 25(OH)D from subsets of serum from study populations and model coefficients1
| If Rval ≤ value3 |
If Rval > value3 |
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| Study (n)2 (ref) | Model type | Value | Intercept 1 | X1 | Value | Intercept 2 | X2 | R2 |
| HELENA (178) (15, 16) | Piecewise | 69.1574 | 0.6266 | 0.9064 | 69.1574 | 41.5535 | 0.2965 | 0.76 |
| OPUS School Meal Study (163) (17, 18) | Weighted Deming | — | 1.8686 | 0.8921 | — | — | — | 0.90 |
| Tromsø Study: Fit Futures (168) (19–21) | Weighted Deming | — | 2.6488 | 0.7645 | — | — | — | 0.98 |
| HGS (172) (22) | Weighted Deming | — | 1.6027 | 0.6615 | — | — | — | 0.74 |
| KiGGS (160) (25) | Piecewise | 60.5211 | 9.4005 | 1.0225 | 60.5211 | 52.4099 | 0.3119 | 0.79 |
| NDNS (Old) (91)4 (26) | Piecewise | 62.1396 | 4.3376 | 0.9719 | 62.1396 | 28.0068 | 0.5910 | 0.82 |
| NDNS (New) (115)4 (26) | Piecewise | 83.5082 | 1.2955 | 1.0380 | 83.5082 | 30.3591 | 0.6900 | 0.95 |
| DEGS (163) (27, 28) | Piecewise | 121.9968 | 14.5309 | 0.7715 | 121.9968 | 102.19191 | 0.0529 | 0.79 |
| Tromsø Study–6th Survey (nonsmokers) (168)5 (29–31) | Weighted Deming | — | 12.5531 | 0.9547 | — | — | — | 0.81 |
| Tromsø Study–6th Survey (smokers) (167)5 (29–31) | Unweighted Deming | — | −0.7299 | 0.9047 | — | — | — | 0.75 |
| LASA (158) (33) | Weighted Deming | — | −2.9577 | 1.0375 | — | — | — | 0.93 |
| AGES-Reykjavik (157) (34) | Piecewise | 49.2155 | 7.7011 | 1.0128 | 49.2155 | 27.3969 | 0.6125 | 0.98 |
| Finnish Migrant Health and Wellbeing Study (Maamu) (159) (35, 36) | Piecewise | 91.8081 | 0.0629 | 1.0218 | 91.8081 | 62.7450 | 0.3390 | 0.93 |
X1 and X2 are the slope(s) of the regression line(s). Three studies [Infant’s Nourishment and Nutritional Status (23), Cork BASELINE Birth Cohort Study (24), and New Hoorn Study (32)] required complete analysis of all samples as they had not previously measured serum 25(OH)D and thus were not standardized in the way the other studies were. AGES, Age, Gene/Environment Susceptibility; DEGS, German Health Interview and Examination Survey for Adults; HELENA, Healthy Lifestyle in Europe by Nutrition in Adolescence; HGS, Healthy Growth Study; KiGGS, German Health Interview and Examination Survey for Children and Adolescents; LASA, Longitudinal Aging Study Amsterdam; NDNS, National Diet and Nutrition Survey; OPUS, Optimal well-being, development and health for Danish children through a healthy New Nordic Diet; ref, reference; 25(OH)D, 25-hydroxyvitamin D.
n, number of sera/plasma from statistical algorithm-defined subsets used for regression equation development.
In piecewise regression, the independent variable is partitioned into intervals and a separate line segment is fit to each interval; the change point [serum 25(OH)D concentration] at which this occurs is reflected by Rval in the above equations.
DiaSorin Liaison assay had an assay formulation change during the course of the NDNS survey, and thus “new” and “old” formulation assays are included.
Roche ECLIA assay used in the Tromsø Study–6th Survey 6 overestimates serum 25(OH)D concentrations in smokers, and thus smokers and nonsmokers are standardized separately.