Monday, November 12, 2012

The Worst Graph

One reason for quotes like there are "there are lies, damn lies, and statistics" is because of graphs like these:

This was on the front of this morning with the caption: "Huge US Oil Boom ahead: The U.S. will overtake Saudi Arabia to become the world's biggest oil producer before 2020."

I was shocked at first glance, because I thought oil production was going to go up 10 or 20-fold from the tiny amount in 2011 to the huge amount in 2015.  That does indeed sound huge.  Then I looked at the left y-axis, where I can see it is only going from 8 million to 10 million barrels a day, an increase of about 25%.  

Fine, you say, but you can still easily see that the light blue bar is above the dark blue bar starting in 2025, showing the US overtakes Saudia Arabia.  

I'm afraid not.  The two bars are not Saudia Arabia versus US production but oil versus gas production, and it is not even clear whose production is depicted.  Is the the whole world, the US, Saudi Arabia?  The article puts US production at 5.8 million barrels a day in 2011, so it appears not to be US production, but other sources put it at closer to 9 million, so maybe it is the US.  

Ok, you say, despite the poor caption, at least you can clearly see that gas production begins to top oil production (in whatever country the graph is depicting) around 2025.  

Not really.  Since oil is in millions of barrels per data and the gas is in billions of  cubic meters (per day, per month, per year, who knows?), this is actually not the case.  The year 2030 shows oil at about 10 million barrels per day and gas at nearly 800 billion cubic meters.  Which is more?  Maybe the readers of money can quickly translate these figures into BTUs or some useful measure of production output, but I sure can't tell you.

Fine, you say, but since they start at about the same level, we at least know that gas increases more than oil over the time period.  

Sorry, even that is incorrect.  Look at the scale on the left axis (oil), which starts at 8 and goes to 12, a 50% increase.  The right axes starts at 600 and goes to 800, a 25% increase. Thus, oil goes from 8 to just over 10 (more than a 25% increase) while gas goes from a little over 600 to just little under 800 (less than a 33% increase--maybe a little more than oil but maybe not).

The only thing that appears to be correct about this graph is the year, until you realize that in the first period, there are only four years (2011-2015) while in the other periods, there are five year differences.

Friday, September 21, 2012

Election Polls

With the upcoming election, I have been following my favorite prediction site:  That site has a big map showing current predictions state-by-state as well as the overall electoral vote prediction.  It also shows the senate predictions.  It has been amazing accurate in the past (though, of course, this doesn't mean that the sites predictions wont change considerably between now and the election). The predictions are all based on some sort of averaging of polls, and the site shows the results of each poll.  What I have found interesting (and it has been noted on the site) is that some polls appear to lean toward Obama while others lean toward Romney.  In other words, the polls appear to have biases.

Why?  Theories abound about this, and much of it comes down to the polling methodology.  The most compelling reason I have seen comes from Nate Silver's blog on the New York Times site.  Silver's blog compares traditional polls, which call only land-line phones, with more modern polls, which call cell phones along with land-lines.

As shown by a chart in Silver's blog,  there is a clear and consistent difference in every swing state between the two types of polls, with modern polls leaning toward Obama.  This is consistent with the idea that younger people are both likely to vote for Obama and also more likely to not have landlines.  This issue has been pointed out before, and a Pew Research Report in 2010 noted substantial differences in party affiliation between voters who had a landline and those who only had a cell phone.

There is no doubt that the percentage of homes without landlines is rising rapidly.  See, for example, the CDC Report from last year, showing that about 30% of adults did not have a landline in 2011, about twice the percentages as 2008.  This increase in wireless-only homes does not necessarily mean an increase in bias (more and more Republicans may be shedding their landlines, and thus the bias could fall even as wireless only usage increases).  Still, the departure in the polls indicates that a bias persists.