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74 bytes added ,  11:17, 28 December 2020
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===== Energy (kcal) =====
 
===== Energy (kcal) =====
[[File:OliveOilsEnergyKcalNormalised20201217.png|thumb|center|Distribution of normalised Energy (kcal) (17-dec-2020)]]
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[[File:OliveOilsEnergyKcalNormalisedCorrected20201227.png|thumb|center|Corrected normalised kcal-energy distribution (27-dec-2020)]]
The three peaks seem to indicate that there are three groups. The peak seen around 857 kcal seems a off. We would expect it to be around 900 kcal. Products in this peak belong to 100g group and the per serving group. It looks like the normalisation (which was based on the fats), did not work out well. So what happened?
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The distribution shows three peaks:
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* 856 kcal combines the serving, 100g and the serving in 100ml group
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* 870 kcal
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* 895 kcal
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Th 100g-group products seem to come from the USDA import, but the data was per 100g and not per serving as you would expect for this import. So the normalisation was already done, but wrong.
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The corrected normalisation has well worked out for the serving group, but not at all for the 100g group. We expect that the peak at 856 is the correct one. So what should the correction factor be if we want the peaks to match?
 
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[[File:OliveOilsKcalEnergyDistributionFudged20201227.png|thumb|center|Fudged kcal-energy distribution (27-dec-2020)]]
The canonical energy (kcal) value per serving is 120 kcal. And the canonical energy (kcal) value for the 100g-group is 900 kcal, i.e. 7.5 times larger. Where could this 7.5 factor come from? The conversion to 100 ml plus de conversion to gram, only provides a factor of 7.14. Hence the value of 857 kcal, which we see in the distribution.
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The peak is roughly correct with a factor 1.055 instead of the 1.01 used earlier. No idea where this comes from.
 
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I wonder whether this difference is due to rounding issues. The US style nutritional table likes to have a simple serving size: 1 tablespoon, which translates to 15ml. But are tablespoons in de US measured in milliliters? It says so on the packages. If we calculate the tablespoon-size from 120 and 900 kcal, we get a size of 14.63 ml, i.e. rounded 15 ml. We better use this value for normalisation.
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Or 123 kcal per 15 ml would have been more accurate.
      
==== Correlations ====
 
==== Correlations ====
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| Poly-unsaturated fat (g) || 7.1 || 11.2 || 14.3
 
| Poly-unsaturated fat (g) || 7.1 || 11.2 || 14.3
 
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|}
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==== Accuracy and Variation ====
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How accurate are the listed nutritional values? And has the apparent variation any meaning?
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Many products use the canonical values as indication for their nutritional values, like 3700kJ or 900 kcal. These are probably average values. Note that the listed accuracy is one or two significant digits. This means that it is not worthwhile to add more significant digits. Normally this implies that the variation is ± 50 kcal or 50 kJ (200 kJ?). This corresponds to the spread of values seen in the graphs above.
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One can wonder about the usefulness of products that display the nutritional values with four or five significant digits. Are those values just a reflection of statistical errors, actual differences in olive oils (year, olive, region?)
    
== OFF Conclusions and thoughts ==
 
== OFF Conclusions and thoughts ==
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