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255 bytes added ,  11:17, 28 December 2020
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A closer look reveals that many of these products come from the USDA import or have 1 Tbsp serving size. So they belong to the per-serving-group, but as they lack the nutritional values that such products should have, like transfat, cholesterol, etc. So how can I recognise these? The original per serving data is not available, only the 100 ml data. This can be seen from the values that are a result of conversion, like 93.333333. This is the same fat percentage that we see in the per-serving group. Thus if a product has a fat percentage between 92.9 and 93.6, it should belong to the per serving group.
 
A closer look reveals that many of these products come from the USDA import or have 1 Tbsp serving size. So they belong to the per-serving-group, but as they lack the nutritional values that such products should have, like transfat, cholesterol, etc. So how can I recognise these? The original per serving data is not available, only the 100 ml data. This can be seen from the values that are a result of conversion, like 93.333333. This is the same fat percentage that we see in the per-serving group. Thus if a product has a fat percentage between 92.9 and 93.6, it should belong to the per serving group.
[[File:OliveOilsNormalisedFatDistributionTwo20201226.png|thumb|center|Corrected normalised fat distribution (27-dec-2020)]]
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[[File:OliveOilsNormalisedFatDistributionThree20201226.png|thumb|center|Olive oils corrected normalised fat distribution (26-dec-2020)]]
 
The corrected normalised fat distribution is shown in the graph above. Now some 1400 products have a fat percentage of 100%. Every product that falls the 100% either have indeed less than 100% fat, or are the victim of rounding errors.
 
The corrected normalised fat distribution is shown in the graph above. Now some 1400 products have a fat percentage of 100%. Every product that falls the 100% either have indeed less than 100% fat, or are the victim of rounding errors.
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There still lie a few products under 98% in the per 100mg group.
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There still lie a few products under 98% in the per 100ml group. These products have a fat percentage of 90g per 100ml. Is this a rounding issue?
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===== ° Saturated fat =====
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===== Saturated fat =====
The distribution spans some 4%. Normalisation seems to have worked well.
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The distribution spans some 4%. The corrected normalisation seems to have worked well.
[[File:OliveOilsSaturatedFatNormalised20201217.png|thumb|center|Distribution on normalised saturated fat percentage (17-dec-2020)]]
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[[File:OliveOilsSaturatedFatNormalisedCorrected20201226.png|thumb|center|Corrected normalised saturated fat distribution (26-dec-2020)]]
    
===== Mono-unsaturated fat =====
 
===== Mono-unsaturated fat =====
The range of mono-unsaturated fat spans some 10%. It seems there are two peaks visible in the three groups.
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The range of mono-unsaturated fat spans some 10% with a peak at 71.5% and at 78.5%. The two peaks are present in all four groups. No explanation occurs to me.
[[File:OliveOilsMonosaturatedFatNormalised20201217.png|thumb|center|Distribution of normalised mono-unsaturated fat percentage (17-dec-2020)]]
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[[File:OliveOilsMonoUnsaturatedFatDistributionNormalisedCorrected20201227.png|thumb|center|Corrected normalised mono-unsaturated fat distribution (27-dec-2020)]]
    
===== 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
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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* 870 kcal
 
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* 895 kcal
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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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.
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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)]]
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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.
    
==== 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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==== 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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