Thursday, June 24, 2010

Just to let you know the variation in human studies

When a doctor or medical person talks to you and recommends something it sounds like they know what they are talking about. This is because they have come to understand was is "normal" variation. When I stated to discover how big this variation was I was very concerned. This is because I was used to creating sensors that were very accurate. The correlation between cause and effect is very different between machines and biological systems.

Let me give you an example. You know that vitamin D is important in bone formation and the higher the vitamin D the more calcium is absorbed. This would be considered a basic fact. Well let you show a graph that shows this correlation:

When I was in research we would have called this a shot gun plot. It is the shape that a shot gun creates when you fire it therefore there is no correlation. However because human studies have such higher variation this is considered a correlation.

This is very problematic. Because the level of calcium absorption is so variable, you can't tell the individual what they need to be taking. This is because if you look at the graph some people have the same calcium absorption at 20 mmmol/l level, while others have it at the 120 mmol./l. I look forward to the day when tests are common enough and cheap enough that we can all have our blood levels measured and our supplementation tailored to our needs.

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