Table 1

GRADE (Grading of Recommendations, Assessments, Development and Evaluation) assessment of the strength of evidence for standard weighted meta-analysis for parameters included in Fig. 3 (Standardised mean difference values (SMD) and 95 % confidence intervals)

ParametersSMD95 % CIEffect magnitude* Inconsistency Precision Publication bias§ Overall reliability
Antioxidant activity1·110·43, 1·79ModerateMediumPoorNoneModerate
FRAP0·59− 0·89, 2·06ModerateLowPoorMediumModerate
ORAC1·92− 0·86, 4·71LargeLowPoorStrongLow
TEAC0·250·02, 0·48SmallMediumHighMediumGood
Phenolic compounds (total)0·520·00, 1·05SmallMediumModerateNoneModerate
Flavonoids (total)1·640·09, 3·19LargeMediumPoorMediumModerate
Phenolic acids (total)0·810·18, 1·44SmallLowModerateStrongLow
Phenolic acids 0·590·11, 1·07SmallMediumModerateNoneModerate
Chlorogenic acid1·58− 0·32, 3·49LargeHighPoorMediumLow
Flavanones 4·760·54, 8·98LargeMediumModerateNoneModerate
Stilbenes0·740·19, 1·28SmallLowModerateMediumModerate
Flavones and flavonols1·741·21, 2·28LargeMediumHighNoneGood
Flavones0·950·39, 1·51ModerateMediumModerateNoneModerate
Flavonols 1·971·31, 2·64LargeMediumHighNoneGood
Quercetin0·55− 0·58, 1·69SmallLowPoorMediumLow
Rutin1·10− 0·31, 2·50ModerateMediumPoorNoneLow
Kaempferol1·340·19, 2·50ModerateLowPoorNoneLow
Anthocyanins (total)1·600·59, 2·62LargeLowModerateMediumModerate
Anthocyanins3·811·53, 6·09LargeMediumHighMediumModerate
Carotenoids (total)7·98− 6·22, 22·18LargeMediumPoorStrongLow
Carotenoids 0·47− 0·13, 1·07SmallMediumPoorNoneLow
Xanthophylls 1·060·18, 1·94ModerateMediumPoorMediumLow
Lutein0·51− 0·27, 1·29SmallMediumPoorMediumLow
Ascorbic acid0·330·06, 0·60SmallMediumModerateNoneModerate
Vitamin E− 0·23− 0·46, 0·00SmallLowModerateNoneModerate
Carbohydrates (total)1·540·10, 2·99LargeLowPoorMediumLow
Carbohydrates 0·460·00, 0·91SmallMediumModerateNoneModerate
Sugars (reducing)0·21− 0·23, 0·65SmallLowModerateNoneModerate
Protein (total)− 3·01− 5·18, − 0·84LargeMediumModerateMediumModerate
Amino acids − 0·82− 1·14, − 0·50SmallMediumHighMediumModerate
DM 1·31− 0·65, 3·28ModerateMediumPoorMediumLow
Fibre− 0·42− 0·76, − 0·07SmallLowModerateNoneModerate
N− 0·88− 1·59, − 0·17ModerateLowModerateMediumLow
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Object name is S0007114514001366_inline2.jpg − 0·50− 1·73, 0·73SmallMediumPoorMediumLow
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Object name is S0007114514001366_inline1.jpg − 0·11− 0·38, 0·16SmallLowHighNoneModerate
Cd− 1·45− 2·52, − 0·39ModerateMediumModerateMediumModerate

FRAP, ferric reducing antioxidant potential; ORAC, oxygen radical absorbance capacity; TEAC, Trolox equivalent antioxidant capacity.

*Study quality was considered low because of high risks of bias and potential for confounding. However, we considered large effects to mitigate this sensu GRADE; large effects were defined as >20 %, moderate effects as 10–20 % and small as < 10 %.
Inconsistency was based on the measure of heterogeneity and the consistency of effect direction sensu GRADE.
Precision was based on the width of the pooled effect CI and the extent of overlap in the substantive interpretation of effect magnitude sensu GRADE.
§Publication bias was assessed using visual inspection of funnel plots, Egger tests, two fail-safe number tests, and trim and fill (see online supplementary Table S13). Overall publication bias was considered high when indicated by two or more methods, moderate when indicated by one method, and low when indicated by none of the methods. The overall quality of evidence was then assessed across domains as in standard GRADE appraisal.
Outlying data pairs (where the mean percentage difference between the organic and conventional food samples was over fifty times higher than the mean value including outliers) were removed.