Archive for the ‘Statistics’ category

Student-Staff Ratios and Results

November 10th, 2009

Nathan just posted this really interesting visualisation of the influence of Student-Staff ratios on SAT scores in the US.  What it implies is that lower ratios tend to result in better scores, but not always…


You can see an additional chart for ‘Math’ and some more comments on the data in the original post.  Nathan quotes the data as being sourced from the US National Center for Education Statistics.  I’ve had a quick peep at the site and there seems to be a huge amount of data there.  If only I had more time…

Back to the Future

September 26th, 2009

Anyone with children will know all about regression; when behaviour goes backwards and you wonder what on earth just happened.  As adults we are also prone to regression and at work and under pressure many of us revert to behaviours that aren’t ones we would probably choose in some of our less pressured moments.

The actual term regression is attributed to Francis Galton, a prolific 19th century statistician (amongst many other things) and a half-cousin of Charles Darwin.  In a statistical context, the term refers to the relationship between the selected values of x and the observed values of y which when used correctly can be incredibly powerful and enable the prediction of future events.

I’m particularly interested in regression at the moment because I want to further refine my thinking on scatterplots that appear to show a reliable correlation between course searches and enrolments.  I’ve had very little formal training in statistics so when I spotted Stephen Few’s positive review of an O’Reilly publication called Head First Data Analysis, I thought I’d give it a go.


What a great book.  OK, some of it is a little basic, but the 80-odd pages on statistical regression are just fantastic and walked me through the basic concepts and then extensions of them effortlessly.  The Head First series isn’t something I’ve seen before but I really like the approach they use – the idea of keeping your brain busy and focussed on the content while learning some fairly detailed concepts – something I always struggle with when reading drier, more academic publications.  I managed to consume all 400-odd pages in the course of a return flight to Sydney so I’d consider it light reading and highly effective.

If like me you now have a hunger for more detail, there is a reference to our old friend Edward Tufte right at the end of the book.  In the 70’s Tufte published a book on regression called Data Analysis for Public Policy which is jammed full of theory and relevant examples.  The best bit of all is it can be downloaded for free here.

Education – Still better value than Sliced Bread

June 12th, 2009

I finally got back to looking at those CPI figures I posted a couple of weeks ago and comparing the overall rate of change for the last 8+ years across the three major categories.

The annual Q1 education leap isn’t quite so pronounced in this format but what is clear is that the cost of Tertiary Education is managing to stay lower (relatively) than food and possibly not rising as rapidly just of late.  I conclude that there has never been a better time to get a tertiary education (or buy that fancy plasma tv) in Australia…


Education CPI Analysis

June 7th, 2009

I noticed that there was a quite sharp increase in the Education element of the March CPI figures.  This appeared to contradict what I had read elsewhere about the cost of education.  I jumped on the excellent Australian Bureau of Statistics website and found that I could download figures going back many years so did a bit of analysis.

Here is the sum of the quarterly CPI percentage change for Education, and Education broken down into 3 sub-classes for the last 10 years.  It is pretty clear that there is adramatic increase in Q1 and then not much movement at all for the rest of the year.


I dragged in the CPI figures for Food and Audio Visual and Computing categories for the same period and you see a much more standard spread of increase (food) and decrease (technology) prices.

So why might this be?  Well the ABS not only produce these figures but they provide a commentary on them.  In that commentary for Education for March 2009 they say

All education indexes rose in the March quarter, with the commencement of the new school year. Secondary education rose 7.6%, preschool and primary education rose 6.6% and tertiary education rose 3.2%.  Secondary education was the main contributor, mainly due to wide-spread fee increases. Both preschool and primary education fees rose with providers reporting that rises were to cover increases in wages and other operating costs.

The commentary is almost identical for the same quarter for the last 3 years except in March 2007 this extra bit of text was added

The rise in tertiary education was due to rises in all tertiary education fees. Increases in TAFE and HECS fees were the main contributors to this movement.

So what is all this telling us?  Well I think it is saying that as one would expect, the cost of education has risen over the last 10 years in a way that is comparable with the price of food but the difference is the hit comes in the first quarter each year.