Statistical validation of results, as Shaffer described it, simply involves testing the null hypothesis: that the pattern you detect in your data occurs at random. If you can reject the null hypothesis—and science and medicine have settled on rejecting it when there's only a five percent or less chance that it occurred at random—then you accept that your actual finding is significant.
The problem now is that we're rapidly expanding our ability to do tests. Various speakers pointed to data sources as diverse as gene expression chips and the Sloan Digital Sky Survey, which provide tens of thousands of individual data points to analyze. At the same time, the growth of computing power has meant that we can ask many questions of these large data sets at once, and each one of these tests increases the prospects than an error will occur in a study; as Shaffer put it, "every decision increases your error prospects." She pointed out that dividing data into subgroups, which can often identify susceptible subpopulations, is also a decision, and increases the chances of a spurious error. Smaller populations are also more prone to random associations.
In the end, Young noted, by the time you reach 61 tests, there's a 95 percent chance that you'll get a significant result at random. And, let's face it—researchers want to see a significant result, so there's a strong, unintentional bias towards trying different tests until something pops out.
Young went on to describe a study, published in JAMA, that was a multiple testing train wreck: exposures to 275 chemicals were considered, 32 health outcomes were tracked, and 10 demographic variables were used as controls. That was about 8,800 different tests, and as many as 9 million ways of looking at the data once the demographics were considered.
anonymous on 14 Apr 15Cerebral palsy-also known as CP-is a condition caused by injury to the parts of the brain that control our ability to use our muscles and bodies. Cerebral means having to do with the brain. Palsy means weakness or problems with using the muscles. Often the injury happens before birth, sometimes during delivery, or soon after being born. Physical symptoms typically appear in the first few years of life. Cerebral Palsy are frequently slow to reach developmental milestones such as learning to roll over, sit, crawl, smile, or walk. Cerebral Palsy occurs in 1 in every 300 children (Source: Center for Disease Control). Cerebral Palsy is a condition that effects the brain and nervous system and can cause many different symptoms ranging from extremely mild to extremely severe. There are different kinds of CP: spastic, dyskinetic, ataxic, hypotonic, and mixed. We believe Sadie is spastic. Cerebral palsy (CP) children can also have learning problems, speech, problems with hearing or seeing (called sensory problems), intellectual differences, and behavioral or emotional challenges. Cerebral palsy does not always cause serious disabilities. Usually, the greater the injury to the brain, the more severe the CP. Cerebral Palsy (CP) can be mild, moderate, or severe. Mild CP may mean a child is clumsy. Moderate CP may mean the child walks with a limp. He or she may need a special leg brace or a cane. More severe CP can affect all parts of a child's physical abilities.Child with moderate or severe CP may have to use a wheelchair and other special equipment. Cerebral palsy is caused by damage or abnormal development to parts of the brain responsible for controlling muscles and movement. The damage or abnormal growth usually occurs before, during or shortly after birth. Cerebral palsy is a non-progressive but ever changing condition; children with cerebral palsy will have high, low or fluctuating tone in their muscles depending on the level and extent of damage t
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