Sunday, 28 December 2014

The Ocean Health Index - summary & revisited

One Ocean, One Index – a 'Composite Essay' on Opportunities and Limits.

The Ocean Health Index – summary: Ten amalgamated assets
To set up the ocean-health index, Ben S. Halpern and co-workers identified ten "assets" of the human-ocean system [c]. The assets are ranging from "Artisanal Fishing Opportunities" and "Biodiversity" through "Carbon Storage" and "Food Provision" to "Sense of Place" and "Recreation". The assets were selected to cover a wide range of ecological, social, and economic benefits or 'use cases'; in that sense they are a possible choice but not necessarily the most obvious. Some of the assets are composites of sub-assets.

To calculate the index, a composite assessment of the state of each asset is undertaken that is applying reference values, studying current situations and development paths. A score is calculated for each asset, and finally one single number, the average score of the ocean-health index, is calculated. That number describes the state of the human-ocean system as a "composite-asset". Obviously, if different composites of result in the same average score then the index indicates a comparable "healthiness" of the human-ocean system.
Considering mathematics, the average score for the ocean-health index is calculated as the weighted arithmetic average of the individual score of each asset. That choice and its implications will be the subject of the following discussions.
However, before turning to that subject following has to be stressed: Selecting these ten assets, identifying indicators for each, gathering data measuring the indicators is a tedious and complex undertaking. That process itself gives ample space for biases, nuanced choices or simple errors. Improving the ocean-health index is a very valuable subject of research and study. Attempts to improve the index do not render it meaningless; they will, on the contrary, strengthen its role as a means for global benchmarking and comparison that otherwise would be missing. Wilfried Rickels and co-workers discuss methodological improvements, while recognising the legitimacy of the data on which it is based. However, these improvements have other limitations that argue for the initial approach of Ben S. Halpern and co-workers.
The annual ocean-health index is calculated at regional level, for coastal seas or Exclusive Economic Zones of countries, for high sea areas, and at global level for the world ocean. For 2012 to 2014, the score of the ocean-health index for the world ocean was estimated to be a modest ~65 of 100. The score for Exclusive Economic Zones of different countries varies between "below 50" and "above 90". Compared to the average score the scores for individual assets may differ considerably. For example, Belgium scores about 100 for coastal protection scores, about 30 for tourism/recreation and has an average score of around 80 for its EEZ.
The index is designed to compare different natural and economic settings and different choices how countries manage their Exclusive Economic Zones. Thus the question arises what is implied when the average score of the ocean-health index for the EEZ of Norway and Netherlands is about 80 and the average score for Iceland's EEZ is about 70. Looking for detail, e.g. what are the scores for single assets, one notices that the scores for single assets vary in a different manner for each of the countries.
In face of these variations the question arises, what kind of simple guidance a manager or the public can get. Consequently one may turn back to the average score and conclude: Norway and Netherlands manage their EEZ equally well and, overall, a bit better than Iceland. If correct, than this is a bold statement. Consequently the question moves into focus "how the average score is obtained?"

The Ocean Health Index – revisited: intermediate level of substitution
Recalculating the ocean-heath index with a modified methodology to estimate the average score [2], showed a considerable dependence of the ocean-health index on the choices for the substitution possibilities including substantial swings of countries between camps of comparatively "well-performing countries" and "under-performing countries". The bulk result of the study [2] is that the global ocean-health index decreases by 20%; namely from a score of 65 of 100 to the score of 52 of 100 if the "weighted arithmetic average" is replaced by a revised methodology limiting substitution among assets. The revised index reduces less-realistic possibilities for offsetting poorer performances in certain assets by better performances in other assets. The associated drop of the global ocean-health index is important, and possibly many decision makers, who would find a score of 65 of 100 "still tolerable" - two good for one bad -, would modify that view for a score of 52 of 100.
Even more striking is the finding [2]:“...when we turn to the assessment of individual countries. Countries with an unbalanced performance across the assets significantly deteriorate in the ranking compared to countries with a balanced performance. For example, Russia and Greenland fall in the ranking for 2013 by about 107 and 118 places (out of 220) respectively, while Indonesia and Peru improve by about 78 and 88 places respectively.” Similarly striking changes are observed regarding the assessment of change over time, for one out of four countries the direction of change is inverted.

These changes of the score of the index in function of the mathematical method is worrisome. An overall shift of scores likely is a simple feature with less impact on management choices. However inverting either relative ranking positions or trends are changes that put in question the usefulness of the index as management tool.

No comments:

Post a Comment