PEREZGONZALEZ Jose D (2012). BNI of kinds of potato chips (inferential statistics). Journal of Knowledge Advancement & Integration (ISSN 1177-4576), 2012, pages 292-295. [Printer friendly]
BNI of generic brands (inferences)
Some potato chips6 are sold under generic brands (eg, a supermarket brand) while others are sold under proprietary brands. Thus, it is of interest to test whether the type of brand informs about overall nutritional balance (BNI) and, thus, whether it may help choose more balanced products. As part of his research on the nutritional balance of potato chips, Perezgonzalez (2012b)3 also assessed whether generic and proprietary brands differed in regards to overall nutritional balance. This article provides inferential information both about the sample of products under research (foodBNI) as well as about hypothetical diets based on those products (dietBNI).
foodBNI
Proprietary brands tend to be more abundant than generic brands, overall, also providing more flavors and package sizes. Notwithstanding this, the distribution of nutritional balance between both kinds of product is quite similar, with 95% confidence that their medians and means will be found in practically the same range of balance, respectively (illustration 1). This range is a bit larger for the population of generic brands, probably due to its smaller availability.
| Illustration 1: Food's nutritional balance |
| Non-parametric |
Generic brand |
|
No |
Yes |
| Median CI95 lower |
79.15 |
76.16 |
| Median CI95 upper |
86.75 |
88.60 |
| SPR lower |
5.81 |
3.13 |
| SPR upper |
13.40 |
15.58 |
|
| Parametric |
Generic brand |
|
No |
Yes |
| Mean CI95 lower |
83.58 |
80.41 |
| Mean CI95 upper |
89.82 |
91.31 |
| SD CI95 lower |
8.58 |
6.30 |
| SD CI95 upper |
12.90 |
13.38 |
| (95% confidence interval's lower and upper bounds) |
The similarity of both groups is compounded further when looking at any differences between them. Indeed, there is no difference from a practical perspective (equivalent to less than 0.8% in nutritional balance), the effect size of the group difference is equally negligible (d=0.08), and statistic tests are non-significant both under non-parametric assumptions (Mann-Witney U=331, p=0.64) and under parametric assumptions (t-test(df 61)=0.27, p=0.79).
dietBNI
As part of two hypothetical diets where the corresponding generic and named products contributed the same weight of chips, the resulting nutritional balance would still be highly unbalanced, with 95% confidence of it ranging somewhere between BNI 65.68 and BNI 75.20 for the diet based on proprietary brands, and between BNI 63.77 and BNI 77.26 for the diet based on generic brands (illustration 2).
| Illustration 2: Diet's nutritional balance (potato chips) |
| Named brands |
Protein |
Carbs |
Sugar |
Fat |
Sat.fat |
Fiber |
Sodium |
BNI |
| CI95 lower |
5.9 |
51.7** |
1.5 |
31.9 |
9.4 |
4.4* |
587.9 |
65.68 |
| CI95 upper |
6.4 |
49.7** |
2.1 |
32.9 |
12.7 |
4.4* |
721.8 |
75.20 |
|
| Generic brands |
Protein |
Carbs |
Sugar |
Fat |
Sat.fat |
Fiber |
Sodium |
BNI |
| CI95 lower |
5.0 |
50.8** |
1.0 |
32.1 |
12.7 |
4.4* |
463.7 |
63.77 |
| CI95 upper |
5.4 |
49.8** |
1.5 |
34.0 |
16.0 |
4.4* |
715.0 |
77.26 |
| (Nutrients per 100g; *fiber content estimated from USDA database5; **carbs' upper and lower bounds are reversed8) |
Research approach
Exploratory study for inferring the nutritional balance of potato chips6 in New Zealand.
Design
Quantitative (fixed) in nature, including a descriptive component and a between-group component.
Sample
Stratified sample of 63 potato chip products (Perezgonzalez, 2012a2), including diverse flavors and other relevant categories. Of these products, 15 were from generic brands and 48 were from proprietary brands. The products were collected in a convenient manner from three major national supermarket chains. Notwithstanding this, the final sample covered a large proportion of the population of potato chip products available in such supermarkets. Thus, given the scope of the sample and the national coverage of the retail chains behind the sampled supermarkets, the actual sample is fairly representative of the population of potato chips available to New Zealanders nationwide. It may also partially inform about the population of potato chips available to Australians, as one of the retail chains is Australian-owned and several of the products are imported from (and probably exported to) Australia.
Variables
Variables of interest for this research were the following:
- Weight contribution of seven nutrients (protein, carbohydrate, sugar, fat, saturated fat, fiber and sodium) to 100g of a food product.
- The Balanced Nutrition Index (BNI) of each food product, as calculated from above variables.
- Aggregated information for the sample of products (foodBNI).
- Aggregated information about the individual nutrients for the simulation of potato-chip-based diets (dietBNI).
Materials and procedure
Relevant data were collected in person by purchasing the food products or by capturing such information from the producers' websites if this information was available and was deemed reliable. The data were then assessed using the Balanced Nutrition Index™ (BNI™) technology (see Perezgonzalez, 20111). Missing data for fiber was estimated for the aggregated variable dietBNI from USDA's database (20115).
Data analysis
The sample's data was assessed as per normality (see Perezgonzalez, 2012b3) for the whole sample, as well as for each group. The BNI distribution of the whole sample was significantly non-normal in skewness even when being quite conservative in its assessment (z=3.39, p<0.001, s=0.001, as per Tabachnick & Fidell, 20014). The BNI distribution of the proprietary brands group was within 'normality' when assessed according to above conservative parameters, but not so the BNI distribution of the generic brands group, which showed a very skewed distribution (z=3.57, p<0.001).
Extreme values also appeared at the upper end of both groups, more so within the generic brands group distribution, although such values were not out of the ordinary (for example, the 5% trimmed means were practically similar to the untrimmed mean for both groups).
The present stage of research on the BNI of foods offers little evidence to ascertain the real distribution of nutritional balance in the population of food products, including that of potato chips. In theory, the nutritional distribution of well balanced products would resemble a chi-square distribution, thus, it can be expected that as products move up the scale towards greater unbalance, they may adopt a more normal distribution. Anecdotal evidence of the nutritional distribution of a sample of 1000 food products seems to support such trend towards a normal distribution or, rather, towards an F-distribution.
Given the uncertainty about the nutritional distribution of potato chips in the population, the sample's data was not transformed in any way. Instead, the article provides results to cover both eventualities. On the one hand, that the sample represents the true nature of the population, this being skewed towards higher levels of unbalance; therefore non-parametric results are more appropriate under such assumption. On the other hand, the population is normally distributed, therefore parametric results are more appropriate under such assumption.
The main analyses carried out were both population descriptives (95% confidence intervals) as well as tests of differences for independent groups with their corresponding statistical significance assessed following Fisher-Perez's approach with threshold set at sig≤0.05 (ie, results with 5% or more extreme probabilities), 2-tailed.
SPSS-v18 was used for the computation of variables, including BNI and international indexes, and for inferential statistical analyses.
Generalization potential
Most of the products were either produced locally or imported from Australia. The results of this study may, thus, be generalizable to the following populations (in order of decreasing generalization power):
- New Zealand, nationwide.
- Australia.
- Internationally, if one assumes potato chip products to be of approximately similar nutritional composition anywhere.
The results of this study may also be of interest to the following populations:
- food researchers
- dietitians
- food policy makers
- consumers
