18 September 2017

Political polls – why they work – or don't

Political polls – why do they work – or don’t This is written in the week before the 2017 New Zealand General Election and it is an exciting time. Many New Zealanders are finding political polls fascinating right now. We wait with bated breath for each new announcement – is our team winning this time? If it goes the way we want, we accept the result with gratitude and joy. If not, then we conclude that the polling system was at fault. Many wonder how on earth asking 1000 people can possibly give a reading of the views of all […]
4 September 2014

Sampling error and non-sampling error

The subject of statistics is rife with misleading terms. I have written about this before in such posts as Teaching Statistical Language and It is so random. But the terms sampling error and non-sampling error win the Dr Nic prize for counter-intuitivity and confusion generation. Confusion abounds To start with, the word error implies that a mistake has been made, so the term sampling error makes it sound as if we made a mistake while sampling. Well this is wrong. And the term non-sampling error (why is this even a term?) sounds as if it is the error we make from […]
19 August 2013

The importance of being wrong

We don’t like to think we are wrong One of the key ideas in statistics is that sometimes we will be wrong. When we report a 95% confidence interval, we will be wrong 5% of the time. Or in other words, about 1 in 20 of 95% confidence intervals will not contain the population parameter we are attempting to estimate. That is how they are defined. The thing is, we always think we are part of the 95% rather than the 5%. Mostly we will be correct, but if we do enough statistical analysis, we will almost definitely be wrong […]
20 March 2012

Statistical Misconception Removal

Our central city is being “deconstructed”. That’s the modern word for demolition. We live in Christchurch, New Zealand where many of our buildings were badly damaged by a string of serious earthquakes over the last 18 months, beginning on 4 September 2010. Over a thousand buildings in the central city are being demolished, because they are no longer safe. The larger ones will take up to a year to bring down, and experts have come from other parts of the world to assist in the process. It is pretty sad, really as we love our buildings. But we need to […]
26 January 2012

Sampling Error Isn't

I hope you committed to a response in the box before reading this post. This is an important topic. Recently I read an amusing blog regarding poor sampling technique. The tweet that led to the link called it “a humorous look at sample error”. I’m hoping the person who tweeted meant bad sampling, because the problem is, the story was not about sampling error. And that is because sampling error isn’t. Isn’t what? It isn’t error. It doesn’t occur by mistake. It is not caused by bad procedures. There is nothing practical you can do when sampling to avoid sampling […]