Friend of the blog, Don Schaffner (left, sort of as shown), a professor of food safety at Rutgers University and co-host of Food Safety Talk writes:
I can tell when something is a big news story.
First, I read about it in my news feed from one or more sources. Second, friends and family send it to me. By these two criteria, the recent news about the five second rule qualifies as a big news story. No links to any of the news outlets blathering on about this, except for the Beacon Journal, who contacted our colleague Jeff LeJeune to comment on the story. Props to them for at least checking with a reputable expert (shurley some mistake, he’s Canadian).
barfblog.com readers are probably aware of this story. And it’s a story, or a press release, not a study.
The press release is apparently based on a PowerPoint presentation. The study has not undergone any sort of peer review, as far as I know. Science by press release is something that really bugs me. It’s damned hard to do research. It’s even harder to get that research published in the peer-reviewed literature. And when reputable news outlets publish university press releases without even editing them, that does a disservice to everyone; the readers, the news outlet, and even the university researchers.
I do have to give credit to the Ashton University press officer, who responded promptly to my request for more information when I clicked on the link on the website where the press release was posted. And it certainly is better to have a PDF of a PowerPoint presentation, instead of just a press release. But it’s still not a peer-reviewed manuscript.
A review of the slide set shows a number of problems with the study. The researchers present their data as per cent transfer. As my lab has shown repeatedly, through our own peer-reviewed research, when you study cross-contamination and present the results as percentage transfer, those data are not normally distributed. A logarithmic transformation appears to be suitable for converting percentage transfer data to a normal distribution. This is important because any statistics you do on the results generally assume the data to be normally distributed. If you don’t verify this assumption first, you may conclude things that aren’t true.
The next problem with the study is that the authors appear to have only performed three replicates for most of the conditions studied. Again, as my own peer-reviewed research has shown, the nature of cross-contamination is such that the data are highly variable. In our experience you need 20 to 30 replicates to reasonably truly characterize the variability in logarithmically transformed percent transfer data.
Our research has also shown that the most significant variable influencing cross-contamination appears to be moisture. This is not surprising. Bacteria need moisture to move from one location to another. When conditions are dry, it’s much less likely that a cell will be transferred.
Another problem that peer-reviewers generally pick up, is an awareness (or lack thereof) of knowledge of the pre-existing literature. Research on the five-second rule is not new. I’m aware of at least three groups that have worked in this area. Although it’s not peer-reviewed, the television show MythBusters has considered this issue. Paul Dawson at Clemson has also done research on the five-second rule. Dawson’s research has been peer-reviewed and was published in the Journal of Applied Microbiology. Hans Blaschek and colleagues were, as far as I know, the first lab to ever study this. Although this research was never published, it did win an Ig Noble prize.
If you don’t have any pathogens on your kitchen floor, it doesn’t matter how long food sits there. If you do have pathogens on your kitchen floor, you get more of them on wet food than dry food. But in my considered opinion, the five-second rule is nonsense. I’m a scientist, I’ll keep an open mind. I know what some people in my lab will be working on this summer. And I’ll tell you more about it… after it’s been accepted for publication in a peer-reviewed journal.