Unfortunately, the summary of this research linked to above and the complete article published in the scientific journal both make a major, but all too common, mistake in risk communication. Research in risk communication has shown that one of the main factors that causes people to mis-understand risks is by using odds-ratios to communicate them, and this is exactly what this research has done.

The article, and the summary drives home the point that babies born in the autumn have a 29% greater risk of getting asthma. Looking at the article, you can discover that the normal risk of getting asthma is about 8%. Most people infer from this that the risk of a baby born in the autumn getting asthma must be 37% (8% + 29%). In fact, this is not how it works. If the normal risk of getting asthma is about 8% then when this is increased by 29% the increased risk is actually about 10.3% (8% * 129%). The value of 29% is a relative increase (or an "odds-ratio"), not an absolute increase (which is only 2.3%: 10.3% - 8%).

Of course, the researchers want to make a big deal about their results to increase their funding and further their careers, and the people writing the summary article in the popular press want to increase their readership, so they all use the value of 29% instead of the more understandable, and arguably more important value of 2.3%. The result of all of this self-interest is that the general public gets misled.

Furthermore, the researchers and the people writing the summary try to simplify the story by saying that the rate of increase is 29% (although the absolute increase is about 2%) is true for all babies born in the autumn. In fact, the full results show that it is a much more gradual increase and decline of risk across the entire year, and the difference in the values at the very worst day compared to the very best day is 29% in relative terms, or about 2% in absolute terms. If this was to be averaged across all babies born in the autumn compared to all babies born in all other months (which is what most people assume that the result refers to when reading about it), the actual absolute difference would probably be less than 1%!

There's a big difference between 29% and 1%, and I think it's wrong to mislead people in this way. Hopefully, if you've made it all the way to here in my comment then you'll now know to treat statements of relative risk increases with a lot more caution, and hopefully try to find out what the absolute risk increase is instead (unfortunately, this can often be quite difficult to do).