lies and statistics, statistics, work

Lies, Damned Lies, and Statistics (3): Growth Rates and Cherry Picking

Statistics can be dangerous, as is evident from the previous posts in this series. People making them can make mistakes, or can use them to deceive. And people reading them can misinterpret them. Our treatment of human rights on this blog depends heavily on the use of statistics, and so the quality of those statistics is important. This blog series mentions some of the things that can go wrong.

Statistical mistakes or statistical lies occur in all kinds of fields, not only the field of human rights. Here’s one that is often made in discussions on climate change. It has to do with measuring growth rates (which we also do for human rights).

Kevin Drum has a quote from George Will, and replies with a graph:

George Will [claimed] that “If you’re 29, there has been no global warming for your entire adult life”. … If you’re 29, you became an adult in 1998, and average global temperatures last year were lower than they were in 1998. So: no global warming in your adult lifetime.

Global warming 1998 2008

The earth is actually cooling! But as about a thousand serious climate researchers have pointed out, it’s not true. Global temps have been trending up for over a century, but in any particular year they can spike up and down quite a bit. In 1998 they spiked up far above the trend line and last year they spiked below the trend line. So 2008 was cooler than 1998.

Of course, you can prove anything you want if you cherry pick your starting and ending points carefully enough. For example: The year 2000 was below the trend line and 2005 was above it. Temps were up 0.4°C in only five years! The seas will be boiling by 2050!

Here’s another example of cherry picking start or ending dates in a time series so as to highlight or drown a growth rate (positive or negative), this time more closely related to the issue of human rights (more specifically the right to work).* Compare these two graphs (in the first graph, just look at the red line for “unemployment rate”, the rest isn’t important, for now – I’ll come back to it in a future post because there are other problems with this first graph):

graph number of jobs

(source)

US unemployment rate 1998 present

(source)

The first graph makes the – honest? – mistake of starting in 2003, giving the impression that Bush’s economic policies  brought down unemployment. The second graph, however, gives some more historical perspective because it starts earlier, and shows that unemployment was much lower before Bush (Bush took office in 2000) and that the decrease during his presidency wasn’t so spectacular as the first graph suggests.

Of course, you can’t hold a president responsible for unemployment, at least not exclusively. But then neither should you tweak graphs so as to give the impression that the president’s policies have a beneficial impact (read the title of the first graph).

* Technically, this isn’t a growth rate, just a time series, but the same logic holds.

Standard

3 thoughts on “Lies, Damned Lies, and Statistics (3): Growth Rates and Cherry Picking

  1. Pingback: Lies, Damned Lies, and Statistics (4): Manipulating the Y-axis Scale in Graphs « P.A.P. Blog – Politics, Art and Philosophy

  2. Pingback: Lies, Damned Lies, and Statistics (35): Sample Sizes, Ctd. | P.a.p.-Blog, Human Rights Etc.

  3. Pingback: Lies, Damned Lies, and Statistics (43): Cherry Picking Time Frames | P.a.p.-Blog // Human Rights Etc.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s