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size of your gray matter, and greatly decrease the chances of developing Alzheimer's disease or dementia in older adults, a new study suggests.”Is this conclusion valid?(a) Yes(b) NoAllen, N. “One way to ward off Alzheimer’s: Take a Hike,” msnbc.com, 10/13/10.Observational study – cannot yield causal conclusions.
Statistics: Unlocking the Power of DataLock5Exercise and the BrainHow would you design an experiment to determine whether exercise actually causeschanges in the brain?
Statistics: Unlocking the Power of DataLock5Exercise and the BrainA sample of mice were divided randomlyinto two groups. One group was given access to an exercise wheel, the other group was kept sedentary “The brains of mice and rats that were allowed to run on wheels pulsed with vigorous, newly born neurons, and those animals then breezed through mazes and other tests of rodent IQ” compared to the sedentary miceIs this evidence that exercise causes an increase in brain activity and IQ, at least in mice?(a) Yes(b) NoReynolds, “Phys Ed: Your Brain on Exercise", NY Times, July 7, 2010.Randomized experiment– can yield causal conclusions.
Statistics: Unlocking the Power of DataLock5Randomized ExperimentsIf a randomized experiment yields a significant association between the two variables, we can establish causation from the explanatory to the response variableRandomized experiments are very powerful! They allow you to infer causality.
Statistics: Unlocking the Power of DataLock5How to Randomize?Option 1: As with random sampling, we can put all the names/numbers into a hat, and randomly pull out names to go into the different groupsOption 2: Put names/numbers on cards, shuffle, and deal out the cards into as many piles as there are treatmentsOption 3: Use technology
Statistics: Unlocking the Power of DataLock5Knee Surgery for ArthritisResearchers conducted a study on the effectiveness of a knee surgery to cure arthritis. It was randomly determined whether people got the knee surgery. Everyone who underwent the surgery reported feeling less pain. Is this evidence that the surgery causes a decrease in pain?(a) Yes(b) NoNeed a control or comparison group. What would happen without surgery?
Statistics: Unlocking the Power of DataLock5Control GroupWhen determining whether a treatment is effective, it is important to have a comparison group, known as the control groupIt isn’t enough to know that everyone in one group improved, we need to know whether they improved more than they would have improved without the surgeryAll randomized experiments need either a control group, or two different treatments to compare
Statistics: Unlocking the Power of DataLock5Knee Surgery for ArthritisIn the knee surgery study, those in the control group received a fake knee surgery. They were put under and cut open, but the doctor did not actually perform the surgery. All of these patients also reported less pain!