Peter's stats stuff

Applying statistics and data science 'in the wild'

I write about applications of data and analytical techniques like statistical modelling and simulation to real-world situations. I show how to access and use data, and provide examples of analytical products and the code that produced them.

Latest post »

Recent posts

Luke-warm about micromaps

30 April 2017

Linked micromaps are an ok way of presenting data and are probably the right tool in some circumstances; but they're not as cool as I thought they might be.

More cartograms of New Zealand census data (district and city level)!

25 April 2017

Shapefiles for cartogram by New Zealand Territorial Authority (ie District or City), with area proportional to population in 2013, have been added to the nzcensus package on GitHub.

Cartograms of New Zealand census data

23 April 2017

Choropleth maps are useful ways of using fill colour to show densities, proportions and growth rates by political or economic boundaries, but can be visually problematic when large geographic areas represent few people, or small areas (ie cities) represent many. One solution is a cartogram, and I have a go at using them to present New Zealand census data in this post and accompanying shiny app.

Impact of omitted variables on estimating causal effects - simulations

15 April 2017

It's much more important to get a well-specified model than worry about propensity score matching versus weighting, or either versus single stage regression, or increasing sample size. A regression that includes all "true" 100 explanatory variables with only 500 observations performs better in estimating a treatment effect than any of those methods when only 90 of the 100 variables are observed, even with 100,000 observations.

Exploring propensity score matching and weighting

09 April 2017

Compared to the older style propensity matching to create a pseudo control sample, it may be better to weight the full data by inverse propensity score because it doesn't discard data. Performing a regression (rather than simple cross tabs) after the weighting or matching is a good idea to handle inevitable imperfections. The whole family of methods doesn't necessarily deliver big gains over more straightforward single stage regressions. And if you have omitted material variables you're in trouble whatever you do.

New Zealand election forecasts

26 March 2017

My New Zealand Election Forecasts web page is up; and I have some reflections on election day randomness, and on quality control.

House effects in New Zealand voting intention polls

21 March 2017

I use generalized additive models to explore "house effects" (ie statistical bias) in polling firms' estimates of vote in previous New Zealand elections.

Simulations to explore excessive lagged X variables in time series modelling

12 March 2017

Adding lots of lagged explanatory variables to a time series model without enough data points is a trap, and stepwise-selection doesn't help. The lasso or other regularization might be a promising alternative.

New data and functions in nzelect 0.3.0 R package

11 March 2017

Version 0.3.0 of the nzelect R package now on CRAN includes historical polling data and a few convenience functions

Visualising relationships between children's books

04 March 2017

Statistical methods like hierarchical clustering and principal components analysis can help understand and visualise literary concepts but don't replace reading the books and engaging with them in traditional critical ways!