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 21 Nov 14Types of CP Associated With Muscle Tone Cerebral palsy comes in several types, which may be associated with muscle tone or specific body parts. Those associated with muscle tone include: spastic CP, where abnormally high muscle tone causes problems with movement, usually in the legs and hips; ataxia, which is marked by involuntary muscle movements; athetoid, which prevents sufferers from maintaining a fixed muscle position (for example, grasping and holding); and mixed, where symptoms of both spastic and athetoid CP occur. Cerebral Palsy: Hope Through Research: Detailed information from the National Institute of Neurological Disorders and Stroke, including facts on the causes, risk factors, warning signs, and types of CP. Definitions and Accommodations for Cerebral Palsy: Information on the types of CP and how to accommodate and interact with severe sufferers. From Kentucky's Office for the Americans With Disabilities Act. United Cerebral Palsy Association: Nonprofit organization that offers a nationwide network of affiliates aimed at expanding the rights, freedoms, and opportunities of those with cerebral palsy. Health Encyclopedia: Cerebral Palsy: Facts on the types, causes, prevalence, and accommodations related to cerebral palsy. Provided by the Florida Agency for Health Care Administration. Cost of Cerebral Palsy: Information on the human and economic impact of cerebral palsy, presented in the form of an academic report composed by the Environmental Protection Agency. Types of CP Associated With Body Parts Certain types of cerebral palsy are associated with specific body parts rather than with the general condition of the muscular system. These types include: quadriplegia, in which all four limbs suffer severe motor dysfunction and a general inability to work together; hemiplegia, in which the limbs on one side of the body are severely affected, with the impact more pronounced in the digits; and diplegia, which causes problems with mus
