What is the link between statistics, inactivity and longevity? When people cite health statistics, how can you be sure that what you read can be trusted? Is there a way statistics can help prove or disprove the effect of exercise or inactivity on longevity?
The problem is the following: someone said a while ago that there are lies, damned lies and statistics. Somehow, there is a bit of truth in this statement. With the amount of conflicting statistics coming out of different studies, people have become, and rightly so, a little bit mistrustful of statistics. Fortunately, there are ways to get a feeling about statistics, to know whether you can trust these benefits of a biostatistics tutor numbers or not. Here are a few pointers:
- Do the numbers make sense? Could they have happened by chance alone or could there be an alternate explanations? (Something called a confounding factor). Let's look at a non medical example: in 2012, DoD released statistics that "proved" that increasing the number of people going to the Walter Reed Medical Center in Bethesda had decreased the volume of cars around the Center. This makes absolutely no sense! But the numbers were real! What was the catch? It was simple! Because of the fear of getting stuck in traffic, people came in to work much earlier. Which meant that when DoD did their measurement of car volume at their usual time, most people had already arrived, since they had come in much earlier.
- How big is the sample? Usually, it is difficult to conclude anything useful if the number of people studied is less than 30.
- Check to see who paid for the study. Dr Ben Goldacre, author of the book "Bad Science", has called this the cancer of Evidence Based Medicine: pharmaceutical companies will publish only studies that give positive results for their product and will hide all studies that give negative results. So if there is a financial interest and the results are glowingly positive for what is "studied", beware!
Now on to statistics, inactivity and longevity. An Australian study published in the British Journal of Sports Medicine strongly suggests the importance of an active lifestyle. This study analyzed the lifestyle of 11 000 Australians over the age of 25 (a good number) and demonstrated that being inactive and constantly watching TV had as bad an effect on lifespan as smoking. For each one hour spent in front of the TV screen, lifespan would decrease by 22 minutes. Watching 6 hours each day (and many do it) would reduce life span by 5 years. Inactivity also increased the risk of a heart attack.
Watching television increases obesity risk even more than being only inactive... Not only are people watching television inactive, but it was found that spending time in front of the television increases automatic eating without people being aware of the amount of calories taken in.
Is this study big enough? Definitely!
Do these numbers make sense? Intuition tells us that our body is a machine that needs to move. Studies on people who were confined to bed showed rapidly a marked decrease in cardiovascular capacity and muscular strength. So yes, the numbers do make sense.
Can results be explained by chance or a confounding factor? The odds of chance explaining the results are very slim given the number of people studied. And as far as I can see, no confounding factor can explain results.
Are there financial interests? Nobody is trying to promote the sale of anything and there does not seem to be any financial interests here.
So it seems this study is to be trusted.
The effect of activity on longevity was looked at in another study out of Taïwan. It indicated that 15 minutes of exercise each day increases life span by 3 years.
One could question the actual numbers. A three years increase in lifespan for every 15 minutes of exercise? Well, maybe. Or maybe not. But the general conclusion does make sense. The take home message is the following: if inactivity decreases lifespan, an active lifestyle increases it. And it does even more: it increases the number of healthy years. You can count on that!