What are they? Causality is when you've got evidence to prove that one variable actually had a direct impact on the results (we'll give examples in a minute). Correlation is when they appears to be a pattern between a variable and the results but we don't have evidence to prove that variable caused the change on the results. Might sound boring / not interesting but bear with us and we'll explain in more detail and explain why it's so important to understand.
To give you and example of actual causality you can think about kicking a football. If you're given the choice to either kick a football or not and then measure whether it's moved position we can say that kicking the football will be the cause of the football moving position. There's a direct, provable link between the two. Now think about the scene of an emergency. 9 times out of 10 the emergency services will be at the scene of an emergency. But there's no direct proof at he emergency services caused the accident. In fact, as we all know, they wouldn't have. The number of emergency services you see just goes up as accidents go up.
The reason this is important to know is because often the media, and even scientific reports e selves get the 2 muddled up. We've seen many a common myth of health and fitness caused by misinterpreting results and making leaps of judgement without prove of the causality. Some examples to think about are below. We're not saying that they're all wrong, but there's evidence out there to at least question their validity.
1) being a little overweight and having increased mortality. BMI would tell you that if you're classed as overweight you'll have higher mortality but does being overweight cause the higher mortality? Or is it the lifestyle choices that are made by overweight people (ie poor nutrition) that causes the mortality rate to rise?
2) cholesterol can be found in the arteries of people that have had a heart attack or suffer heart disease. Doctors and the media will tell you cholesterol therefore causes heart problems. But what if it's the other way around? What if cholesterol is like the emergency services and is in the arteries to try and fix some other form of damage. Does it just correlate with heart disease risk rather than cause it?
3) how about obesity and activity levels. We all have the opinion that people become obese because they're not active enough, but who's to say it's not the other way around? Is it possible that obesity is actually the cause of reduced activity rather than the other way around (there's actually some proof this may be the case).
The message to take away from today is to not just agree with everything you hear in the media, or even on blog websites! If the scientific data is misinterpreted it can have huge impacts on your health. If you can then go and do a little research yourself. Search the web for someone that's gone into the study in more detail and reviewed it's results. Make your own decision rather than relying on the news reader to tell you what's healthy and what isn't. At the end of the day they want drama to keep the news interesting!