Well, here is a graph I found at luftkvalitet.info, and it's a report over the air quality in Bergen. There are two automatic air-samplers in Bergen, one at Danmarksplass and one by the old town hall. The NO2 level and concentration of particles in two different sizes are measured. Each of the components is classified into four different categories, depending on the concentration (as shown in the chart below). The (total) air quality is the reported as one of the categories, depending on the most polluted of the three components. The chart below is from month of November 2009.
Some interesting data can be extracted from this graph. Like that November 2009 where approximately 30 hours longer at Rådhuset compared to Danmarksplass, but on average the years 2003 and 2009 where longer on Danmarksplass.
What I'm getting at here, is (again) that this isn't a very good graph. Personally, I think that they are missing a "no data" category or something, since November has a total of 720 hours, which none of the bars have. And, as I understand the data, the total of all categories isn't interesting, since they are all the same (only depending on how many days in the month). In fact, the interesting data here is the hours with elevated level of air pollution. And due to the large size of the normal (green) bars, the graph does not do a good job in presenting these data. So, here is my suggestion of a redesigned graph, focusing on comparing the data with elevated level of pollution. I opted for a three panel vertical Trellis chart:
To even better compare the individual values, a 1x4 vertical Trellis chart could also been used, wiyh panels Rådhuset Nov 2009, Rådhuset average 2003-2009, Danmarksplass Nov 2009 and Danmarksplass average 2003-2009. Each panel with three horizontal bars with each of the different level of pollution.
Another option would be to include a bar for the total hours with elevated pollution (sum of some, much og severely polluted categories).
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12 comments:
..so the air quality at Danmarksplass is worse than at the old city hall, and whomever designed this format did not have the knowhow required to normalize data?
Mucho improved graphics, btw.
But why in the blue hell didn't they normalize?
And quelle surprise with the results...
.....do you think there could be another axis showing - I don't know - the traffic density at the sampling site - to make a 3D chart or something? :-)
He, he. Yeah, you could do a further analysis if more data where added. :D
I too would normalize the data and report it as % or something. But maybe the thought is that hours is a unit more understandable for people? Or it's the "standard unit" to report these data in? I don't know, I just feel it's a bit weird to report it like this when there are so many hours missing to make a full month...
People are always fed results in percentages though, right? 'Cause when the number of hours exceed familiar values, like 42.5, they stop making sense.
That's a good point, Wilhelm. And I do agree that hours above 24 starts to be confusing.
As for people understanding percentage: If severely polluted where reduced from 10 hours to 5 hours from one month to the next, most (or at least many) people would understand that this is a 50% reduction. Now, if you reduce the time with severely pollution from 10% to 5% from one month to the next, how many will claim that the reduction is 5%?
Actually, I do believe that (bar) graphs do a really good job here, because people can compare length and have a clear understanding of how much the change is. In this case, both hours and % can be confusing. Still, hours that doesn't add up without any explanation why is the worst of the two, in my opinion.
.....do you think there could be another axis showing - I don't know - the traffic density at the sampling site - to make a 3D chart or something? :-)
LOL!
I missed that one the first time. But actually, I've been thinkign about this, due to the restrictions on traffic in Bergen lately. And I would have loved to see three measurements compared: Pollution, traffic and weather (like wind or something?). Of course these three are somewhat correlated, but it would be interessting to see how much they affect each other.
Damn..I just realized that I used 42.5 as an example of a familiar number because I thought that was the average work-week.....
Yeah, I know how it is with you and maths...
:D
I thought you picked 42 due to the hitch-hiker's guide to the galaxy connection...
HAH...outed as nerd :D
...as that wasn't apparent by my posts here at m-factor the last couple of days.
:D
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