A little bit of self-plagiarism doesn't hurt everyone, it seems

We all (hopefully) know that plagiarism is bad. Copying someone else's work and passing it off as your own is definitely not okay. But what about plagiarising your own work? As a senior colleague of mine once noted, there's only so many ways that you can describe the same methods and data, so some degree of self-plagiarism is unavoidable if you are using the same or very similar methods and data in multiple research papers. But how much is too much?

Take the following two snippets:

1. "Compared to other OECD countries New Zealand has a poor crash record. In 1990, New Zealand had the third highest traffic death rate (21.5 deaths per 100,000 population) after Portugal and Spain and ranked the seventh highest out of 21 OECD countries at 3.3 deaths per 10,000 vehicles (Land Transport Safety Authority, 1995). These population and vehicle rates were 58 and 43%, respectively higher than Australian rates, New Zealand’s closest neighbour."
2. "Compared with other OECD countries, New Zealand has a poor crash record. In 1990, New Zealand had the third highest traffic death rate (21.5 deaths per 100 000 population) after Portugal and Spain and is ranked the seventh highest out of 21 OECD countries with 3.3 deaths per 10 000 vehicles (Land Transport Safety Authority, 1995). These population and vehicle fatality rates were 58% and 43% respectively higher than rates in New Zealand’s closest neighbour, Australia."

The first quote is from the introduction in this 2002 article by Paul Scuffham and John Langley, published in the journal Accident Analysis & Prevention. The second quote is from the introduction in this 2003 article by Paul Scuffham, published in the journal Applied Economics. They're pretty similar, wouldn't you agree?

And before you think I'm cherry picking from the articles, you should read them both (the first one is gated, unfortunately). Here's another bit, from the discussion section:

1. "We did not include all policy changes in the model primarily because our aim was to establish a link between economic factors and traffic crashes. Furthermore, there may have been more policy changes than observations and many policy changes are introduced simultaneously with other policy changes making distinguishing the effects of policies difficult – especially if dummy variables are used. Other variables not included were weather conditions and public holidays. These factors may have some explanatory power in forecasting crashes. However, the effects of these factors may be captured in the trend, seasonal or residual components of the STSM."
2. "Not all policy changes were included in the model primarily because the aim was to establish a link between economic factors and traffic crashes. Furthermore, there may have been more policy changes than observations, and many policy changes are introduced simultaneously with other policy changes making distinguishing the effects of policies difficult – especially if dummy variables are used. Other variables not included were weather conditions and public holidays. These factors may have some explanatory power in forecasting crashes. However, the effects of these omitted factors may be captured in the trend, seasonal or residual components of the STSM."

Virtually the entire introductory section, and data and methods section, are identical in the two papers. The results are slightly different between the two papers because the dependent variables were specified slightly differently, but in the main, the results and discussion sections are incredibly similar as well (as the quotes above illustrate).

It's difficult to know how often this sort of thing happens (although Retraction Watch will give you some idea). I only picked it up in this case because I happened to read both of those articles consecutively, as part of background reading for a research project on road accidents in New Zealand (more on that in a future post). It's also not clear where the threshold is between acceptable and excessive self-plagiarism, and no guidelines exist (that I'm aware of).

The key point here is that this is essentially one journal article, and the authors have received double value for by publishing it twice. It's impossible to know their motives for this. At best, this is innocent and lazy writing. At worst, it is a cynical gaming of the publication system. Either way, it certainly hasn't hurt Paul Scuffham, who is described in his Griffith University profile as "one of the leading and most productive health economists in Australia and internationally". However, it's easy to be productive when you publish the same thing multiple times.