Being in a Good Mood Won’t Make Your Flu Shot More Effective
It’s almost flu season, which means flu shot season. The New York Times suggests that being in a good mood can improve your immune response to vaccinations, which gives you another reason to happily head to the pharmacy. It is a pity that this pleasant title is supported only by fragmentary statistics.
Headline: Upbeat Mood May Boost Effectiveness of Flu Shot
History: Flu shots are not 100% effective – although let me say this first: if you can get one, you should – and scientists don’t know all the variables that affect that effectiveness. They do know that age is a factor, for example: for young people, the flu vaccine is 70 to 90 percent effective, and for older people it drops to 17-53 percent. Therefore, the authors of this study decided to test the influence of a variety of behavioral and psychological factors on the effectiveness of the vaccine in elderly patients.
In this study, 122 seniors recorded their diet, sleep patterns, exercise, stress, and mood for two weeks before and 16 weeks after the flu shot. They were tested for influenza antibodies four and 16 weeks after vaccination to evaluate the effectiveness of the vaccine.
This is where statistical Jiu Jitsu comes into play. The researchers had a lot of data to compare: on the one hand, the effectiveness of the vaccine at two time points; on the other hand, all these lifestyle factors are looking for trends and correlations. There is a lot of math under the hood here to identify results that are “statistically significant,” meaning they don’t look like the result of chance or luck.
The researchers found that the correlation between positive mood and vaccine efficacy was statistically significant. However, they did not correct the fact that they tested nearly a dozen possible influences on the result. This is a big problem for their conclusions. The more comparisons you make, the more likely it is that one of them will be recorded as statistically significant just due to random sampling error.
Rebecca Goldin, professor of mathematics at George Mason University and director of STATS at Sense About Science, USA , put it this way:
In this study, the authors made so many comparisons that some kind of smoking gun could appear, whether there is a real relationship or not. […] This study does not provide statistical evidence for or against the scientific hypothesis that mood influences vaccine efficacy.
The authors acknowledge this in the study: “Due to the exploratory nature of this analysis and the desire not to increase type 2 errors, corrections for multiple comparisons were not applied.” They are correct that if they corrected multiple comparisons, they would risk type 2 errors or false negatives, but the tradeoff was that their method allowed for false positives. It was impossible to come to a firm conclusion from a study with so many comparisons. Without more focused observation, we know nothing at all.
Conclusion: The authors of this study told the New York Times that “they were unable to control all possible variables, and that their observational study does not prove causality.” Yeah, that doesn’t prove anything. Being in a good mood is great, and so are flu shots, but as far as the connection between the two is concerned, the current data is pretty much it.