Numbers Do Matter – Another Weightings Discussion
Numbers do matter. With different weightings applied to the main categories considered by the consultants, the results change and Kettle Island drops out of the #1 position. If you’re interested to hear more, keep reading.
In simple terms, weightings define how important each factor (or category) is when determining the overall project recommendations. Within their findings and recommendations, the consultants have presented a Sensitivity Analysis (slide 15) of weightings and results. The intent of this slide is to deflect any criticism around the weightings assigned to the factors that were considered for the analysis.
This slide depicts the overall results of varying weightings for every major category. For example, within the current analysis, where Kettle Island is ranked #1, Traffic and Transportation is assigned a weighting of 29%. This slide attempts to answer the question: “How does the overall ranking of alternatives change when the weighting of Traffic and Transportation is changed from as low as 15% to as high as 40%? ” This same process is done for every major factor, with the range of values tested varying for each factor.
According to this slide, through every high / low variation tested for each major factor, Kettle Island ranks as the overall #1 selection every time (I’ve read and heard others misinterpret this slide to mean that Kettle Island ranked #1 in every category analyzed – this is not the case, nor is it the intent of this slide).
This doesn’t sit very well with me.
Let me assure you that the results most definitely are sensitive to the weightings assigned to each category. For argument’s sake, let’s consider these weightings, which I believe to be sensible, and see how this impacts Kettle Island’s overall ranking. I haven’t changed any of the data provided by the consultants other than the weightings applied to the major categories. For comparative purposes, the consultants’ weightings are in shown brackets.
Traffic and Transportation: 20% weighting (29%)
Natural Environment: 20% weighting (17%)
Cultural Environment: 20% weighting (9%)
Water Use and Resources: 10% weighting (5%)
Socio Economic Environment: 7% weighting (7%)
Land Use and Policy: 8% weighting (8%)
Cost: 15% weighting (26%)
With these weightings, the results are very different. The 10th Line crossing becomes the #1 choice, and Kettle Island ranks in a virtual 3-way tie for second place with Gatineau Airport and Lower Duck. In another scenario, with equal weightings applied to all major categories, 10th Line again comes out on top, with Kettle Island in 2nd place.
The main point I’m trying to make here is that the numbers do matter. Don’t let slide 15 fool you. With different weightings applied to the major categories, the results change.
But most of all, don’t forget that these are just numbers. At the end of the day, the numbers should be inputs into the final decision, but they should not be the sole basis of the final decision.
They need to be balanced with some common sense.
For more information about the categories and weightings, please refer to these earlier postings: Who determined the evaluation weightings? and Selection Process – Flawed Analysis?
Loading ...
September 23rd, 2008 at 9:35 am
I agree with the above posting. Any result can be obtained by changing the weightings of the major categories or sub-items or the number of these categories.
Why is there so much weight to cost, traffic and transportation where the long term cost to a community (included in cultural environment) is discounted? We should be building livable cities and not creating a barrier that will affect 100,000 people.
Also, am I reading the details correctly that they say there are no emission concerns with Kettle Island. I find this very hard to believe.
September 23rd, 2008 at 9:44 am
You are absolutely correct about emissions. Although there is a factor dedicated to quantifying the impact of harmful emissions on people, the consultants have concluded that there will be ZERO people negatively impacted by these emissions for the Kettle Island Corridor. I also find this very hard to believe.
September 24th, 2008 at 12:38 pm
For bilinguism purposes, my article is written in french and english.
The consultants only gave 9% weight to the impact on residential communities, institutions and national heritage sites (misleadingly labeled “cultural” in the study) whereas they gave 29% weight to an insignificant (25%) reduction of truck traffic on King Edward. The consultants only gave the natural environment 17% weight versus 26% to costs, completely unacceptable in 2008. The Kettle Bridge’s pollution would directly affect 100,000 residents living close by.
Cette pollution est une diffusion directe ou indirecte dans l’environnement de polluants. Ce sont souvent des sous-produits involontaires d’une activité humaine, comme les émissions des pots d’échappement.
Les particules en suspension (notées PM en anglais pour Particulate Matter) sont d’une manière générale les fines particules, portées par l’eau ou l’air et que l’on peut recueillir et quantifier par filtration ou par d’autres procédés physiques.
Selon la taille des particules (diamètre aérodynamique ou diamètre aéraulique), on distingue en métrologie les PM 10, les PM 2,5 ou les PM 1 selon la taille des particules en micromètre (10-6 m).
• PM 10 particules en suspension dans l’air, d’un diamètre aérodynamique ( ou diamètre aéraulique) inférieur à 10 micromètres. Les particules plus fines peuvent être référencées :
• PM 2,5 dont le diamètre est inférieur à 2,5 micromètres, appelées particules fines
• PM 0,1 dont le diamètre est inférieur à 0,1 micromètre, appelées particules ultrafines
ces particules fines pénétrent plus ou moins profondément dans le système respiratoire. Des particules de type PM2,5 par exemple arrivent jusqu’au niveau des alvéoles pulmonaires.
L’OMS a estimé que le taux actuel de particules dans l’air est un facteur de diminution de l’espérance de vie ;
• de 8,2 mois dans l’Europe des 15,
• de 10,3 mois dans les dix nouveaux États de l’UE (plus pollués).
Dans l’Europe des 25, ce sont environ 348 000 morts prématurées par an qui sont attribuées à cette polllution.
• Les effets sont trois fois plus élevés là où sont concentrés les transports et émissions de chauffage ou centrales thermiques mal filtrées (par rapport aux zones moins polluées)
• Les PM de taille inférieure à 2,5 micromètres (PM2.5) sont les plus dangereuses.
• Un rapport EMEP a montré qu’en 2005-2006 de nombreuses grandes villes européennes étaient très polluées par les particules, avec des teneurs moyennes en PM2.5 dépassant quotidiennement et annuellement – et de beaucoup – les seuils, valeur limites ou directives de l’OMS (qui sont plus strictes que les limites européennes).
Les valeurs limites OMS sont aussi dépassées dans des secteurs de taille très significative en aval de zones urbaines denses, suite au transport des petites particules par le vent.
Few investigators have specifically addressed the particle lung doses from fine and coarse PM. Venkataraman & Kao (1999) showed that on a mass basis, the proportion of fine PM being deposited in the pulmonary region is three times larger than the proportion of coarse PM. The number dose to the pulmonary region, however, was five orders of magnitude higher for fine than for coarse PM. This indicates that if effects of PM would even [be] partly related to particle number, the fine fraction completely dominates effects related to pulmonary deposition.
Long-term ambient exposure to current ambient PM concentrations may lead to a marked reduction in life expectancy. The reduction in life expectancy is primarily due to increased cardio-pulmonary and lung cancer mortality.
Increases are likely in lower respiratory symptoms and reduced lung function in children, and chronic obstructive pulmonary disease and reduced lung function in adults.
Common sense never seems to prevail in this decision making.