Author: Geoff Cumming

Video too slow? Then speed it up!

Video lectures can sometimes drag, maybe even statistics videos? Did you know that YouTube lets you adjust the playback speed? Simply go to ‘Settings’, the little cogwheel lower right, choose ‘speed’, and select from the options. Often, speeding up to 1.25 or 1.5 can be good. Of course, you can pause, rewind, or tweak the speed up or down at any moment. Better still, pause, write down the main messages in your own words, then watch some more.

You might even like to fiddle with the speed of the ITNS videos, which are all on YouTube, as described in this post.

Happy (fast?) watching.

Geoff

Geoff on Sydney radio: p hacking

Wendy Harmer is a great comedian and also a high-rating host on Sydney chat radio. Recently I (Geoff) had great fun chatting with her about p hacking, following my article in The Conversation on that topic. (See earlier post.)

Here’s our chat:

 

Trying to keep it simple, I describe just 3 tools, or questions, that are worth having in the toolkit for the intelligent and sceptical reader of a report of a research result, in the mass media. They are the take-home message. Keep handy at all times!

Geoff

MoE, the Margin of Error: What the New York Times says

The title of this NYT article is a good summary: “When You Hear the Margin of Error Is Plus or Minus 3 Percent, Think 7 Instead”. The NYT piece is based on this article by famous statistician (imagine that!) Andrew Gelman and colleagues.

But first, a few words about Chapter 1 in ITNS. A fictional poll reports 53% support for a proposition, with margin of error (MoE) of 2%. So the 95% confidence interval is [51, 55]. This CI tells us about the sampling variability, according to our statistical model and N for the poll.

OK, but later in the chapter we discuss how, in real life, there’s even greater uncertainty–extra reasons why the poll result may differ from the true level of support in the population of all likely voters. Perhaps the poll sample doesn’t represent that population well? What about the people who couldn’t be reached by the pollster, or who refused to answer the question? Was the poll question loaded in any way? Unfortunately, the confidence interval can’t tell us about all that.

Gelman and colleagues investigated more than 4,000 U.S. polls for more than 600 presidential, senatorial, and state governor elections since 1998. All the polls were conducted in the final three weeks of the election campaigns. They compared the polls with the election results to estimate total error, which they found to be considerably larger than sampling variability as indicated by the pollster’s stated MoE.

So, yes, in real life polls do typically have uncertainty beyond sampling variability. Furthermore, the Gelman team could estimate that this extra uncertainty is often considerable. Their conclusion was the NYT title: On average, the polls reported MoE of around 3%, but the researchers found total uncertainty was more like a 7% error.

So now we can go back and read Chapter 1 again, with confidence that there’s evidence to back up our discussion, and even to give us a rough idea about the typical amount of extra uncertainty, at least for recent U.S. political polls. Take-home message: There’s often more error than we appreciate. Alas!

 

Are you hearing ‘The Conversation’? This time on p hacking.

‘The Conversation’ is a non-profit online publication with the tag line ‘academic rigour, journalistic flair’. Starting in Australia a few years back and, at first, largely funded by universities, it is spreading worldwide, with editions in a number of countries, and recently a global edition. Articles are mainly written by academics (university faculty) with much editing for accessibility. It’s all free, and I find the daily email bulletins increasingly timely and interesting. It covers an incredible range of topics. Follow the US Presidential  campaigns, Brexit, climate change, or what you will. Timely and intelligent.

I mention this as a preview to mentioning my post of a couple of hours ago on p hacking and the replication crisis. I find an excuse to mention estimation and the new statistics. But you expected that. Feel free to add a comment in response to my post if you wish.

Now streaming from YouTube: ITNS videos

There are 38 videos that come with ITNS. They aim to explain ideas and, in many cases, to walk through using ESCI to see cool things, or analyse data and make nice data pictures. Pictures with CIs, of course.

I’ve uploaded those videos to YouTube, for easy streaming. At YouTube, search for ‘ITNS book’. The first digit in the name is the chapter number. The text below the vid on YouTube summarizes the content.

If instead you search for ‘Geoff Cumming’ you get in addition a dozen or so earlier videos, including the original dance of the p values. (Another way to find that is to Google ‘dance of the p values’.)

Back to the ITNS vids. Early feedback from students has been positive. “Not too fast, not too slow.” (Goldilocks?) “Great that they are pretty short.” (I’m believing that’s a positive remark.)

Enjoy.