4-Point Efficiency Comparator
Comparator figures will be displayed only when data for two gardens is entered in the form, and only when data for each garden is sufficient enough to generate ratings for all four efficiencies having a score.gifmark. The average of all four are displayed in a set of percentage figures that add up to 100%. When each garden has a 50% score, both are equally efficient, even though individual efficiencies may vary. The spread between these two figures is the relative difference in efficiencies between the two gardens.

Intended for those with a general interest in overall efficiency, the 4-Point Efficiency Comparator provides a single unbiased representation of all four efficiencies combined. Those with special interests, however, can still focus directly on an individual efficiency rating to decide which is the more efficient garden in that regard.

It's important to understand that, unlike individual efficiency ratings, Comparator scores are not absolute. They are relative (to each other). When an efficiency rating for one garden changes, the scores for both gardens are affected. Thus, to have meaning, a Comparator score for one garden should not be taken out of the two-garden context in which it was originally formulated.

How Comparator Scores are Computed
In order to provide a single unbiased average of all four efficiencies combined, a simple average cannot be taken directly from raw efficiency ratings. An issue with their unequal numeric scales must first be addressed or the overall average will be biased in favor of efficiencies using larger numbers. For example, grams/sqft (space) uses a larger numeric scale than grams/kwh (energy).

Individual
Efficiency
Ratings

Simple
Averaging
(biased)

Comparator
Scoring

Comparatorscore.gif
Averaging
(unbiased)

score.gif
Space

score.gif
Energy

Space

Energy

1

60.1

0.94

30.52
(60.1+0.94)/2

0.6663
(60.1/90.2)

0.3072
(0.94/3.06)

48.7%
(.6663+.3072)/2

2

30.1

2.12

16.11
(30.1+2.12)/2

0.3337
(30.1/90.2)

0.6928
(2.12/3.06)

51.3%
(.3337+.6928)/2

sum 90.2 3.06 Math is shown in dimmed font

Looking at the Individual Efficiency Ratings in the table to the right, notice how garden 1 is 1.99 times more space-efficient, while garden 2 is 2.25 times more energy-efficient (you can confirm by dividing the smaller rating into the larger one). Given that garden 2 is more energy-efficient than garden 1 is space-efficient we know that garden 2 is slightly more efficient overall. Yet when looking under Simple Averaging, the results not only point to the wrong garden but greatly exaggerate the difference between them.

To overcome this problem, the Comparator sums the original ratings for each efficiency (see underlined figures) then uses that as a base upon which to build individual relative scores that share a common scale of 1 . It then averages those individual scores instead of the original ratings. As you can see under Comparator Averaging, garden 2 rightfully has the better overall score and without exaggerating the difference.

It is this kind of objectivity - giving each efficiency equal importance while still maintaining the relative differences between gardens - that the Comparator carries to its results. Although only two efficiencies were used here to make a point, the Comparator actually performs the same computations with all four.

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