Collecting Data: Randomized Experiments

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1 STAT 250 Dr. Kari Lock Morgan Collecting Data: Randomized Experiments SECTION 1.3 Randomized Experiments Exercise and the Brain A study found that elderly people who walked at least a mile a day had signibicantly higher brain volume (gray matter related to reasoning) and signibicantly lower rates of Alzheimer s and dementia compared to those who walked less The article states: Walking about a mile a day can increase the 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) No Allen, N. One way to ward off Alzheimer s: Take a Hike, msnbc.com, 10/13/10. Exercise and the Brain How would you design an experiment to determine whether exercise actually causes changes in the brain? Exercise and the Brain A sample of mice were divided randomly into 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 mice Is this evidence that exercise causes an increase in brain activity and IQ, at least in mice? (a) Yes (b) No Reynolds, Phys Ed: Your Brain on Exercise", NY Times, July 7, Randomized Experiments If a randomized experiment yields a signibicant association between the two variables, we can establish causation from the explanatory to the response variable Randomized experiments are very powerful! They allow you to infer causality. How 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 groups Option 2: Put names/numbers on cards, shufble, and deal out the cards into as many piles as there are treatments Option 3: Use technology 1

2 Knee Surgery for Arthritis Researchers 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) No Control Group When determining whether a treatment is effective, it is important to have a comparison group, known as the control group It 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 surgery All randomized experiments need a control or comparison group (could be two different treatments) Knee Surgery for Arthritis In 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. Clinical Trials Clinical trials are randomized experiments dealing with medicine or medical interventions, conducted on human subjects Clinical trials require additional aspects, beyond just randomization to treatment groups: Placebo Double- blind Source: The Placebo Prescription, NY Times Magazine, 1/9/00. Placebo Effect Often, people will experience the effect they think they should be experiencing, even if they aren t actually receiving the treatment. This is known as the placebo effect. Example: Eurotrip One study estimated that 75% of the effectiveness of anti- depressant medication is due to the placebo effect A review of 15 clinical trials with different diseases found that 35% of patients were satisfactorily relieved by the placebo alone (The Powerful Placebo) For more information on the placebo effect (it s pretty amazing!) read The Placebo Prescription or listen to Radiolab s podcast Placebo Study on Placebos Blue pills are better than yellow pills Red pills are better than blue pills 2 pills are better than 1 pill 4 pills are better than 2 pills And shots are the best of all! 2

3 Placebo Effect Placebo- controlled studies Control groups should be given a placebo, a fake treatment that resembles the active treatment as much as possible This allows researchers to separate effect of treatment itself from effect of the placebo effect Often instead of a placebo, new treatment is compared to the existing standard treatment (not ethical to not help a patient in need) Should doctors be allowed to prescribe placebos? Double- Blind Experiments If possible, randomized experiments should be double- blinded: neither the participants or the researchers involved should know which treatment the patients are actually getting The participants should be blinded because of the placebo effect The researchers should be blinded to avoid conscious or unconscious bias of the results SildenaSil and cgmp The molecule cgmp is a natural vasodilator: it increases blood Blow by relaxing muscle in the walls of blood vessels. SildenaBil inhibits phosphodiesterase (an enzyme), which degrades cgmp. sildenasil Blood vessel cgmp phosphodiesterase degrades cgmp SildenaSil 1980s: PBizer develops sildenabil citrate, which inhibits phosphodiesterase, hoping to increase blood Blow in the coronary arteries of individuals with heart disease. 1991: Phase I clinical trials are begun. 1992: PBizer gets reports of an unexpected side effect in men. 1994: After sildenabil fails to show any cardiac benebit, PBizer begins pilot studies for treatment of erectile dysfunction (ED). 1998: FDA approves sildenabil, marketed as Atenonol: A randomized experiment Silvestri et al assigned 96 men to take atenolol, a heart drug which can cause ED as a side effect: 32 men were told they were taking either atenolol or placebo 32 were told only that they were taking atenolol 32 were told that they were taking atenolol, and that it can cause ED as a side effect. After 3 months, the researchers asked men to report any experience of ED. Silvestri A, Galetta P, Cerquetani E, Marazzi G, Patrizi R, Fini M, Rosano GM. Report of erectile dysfunction after therapy with beta- blockers is related to patient knowledge of side effects and is reversed by placebo. Eur Heart J Nov;24(21):

4 SildenaSil: A Randomized Experiment The researchers then assigned all men who d experienced ED to either 50mg sildenabil or placebo. The men were blinded regarding this treatment. After a week the researchers asked the men if their ED had improved. Any guesses what the men reported? They were all on the same drug! 32 men had been randomized to atenolol and told it can cause ED 5 randomized to take Viagra (blinded) 10 reported experiencing ED 5 randomized to take placebo (blinded) Trustworthy Clinical Trials To assess the trustworthiness of results from clinical trials (or any medical result), ask Was the treatment randomly assigned? Was the control group given a placebo or other treatment? Was the study double- blind? All improved! All improved! Control, placebos and blinding are important! Green Tea and Prostate Cancer A study was conducted on 60 men with PIN lesions, some of which turn into prostate cancer Half of these men were randomized to take 600 mg of green tea extract daily, while the other half were given a placebo pill The study was double- blind, neither the participants nor the doctors knew who was actually receiving green tea After one year, only 1 person taking green tea had gotten cancer, while 9 taking the placebo had gotten cancer Green Tea and Prostate Cancer A difference this large is unlikely to happen just by random chance. Can we conclude that green tea really does help prevent prostate cancer? (a) Yes (b) No 4

5 Matched Pairs In a matched pairs experiment, either each case gets both treatments, in random order, or cases are paired and each pair gets both treatments (randomly assigned). Compare a case to itself or a similar case Look at differences in response within the pair Useful when the response variable varies a lot from case to case Gatorade and Running Does drinking Gatorade make you run faster? Variables: Explanatory: drink Gatorade or placebo before running Response: time to run a certain distance (a mile?) Completely randomized: Randomize half of the people to drink Gatorade half to drink a placebo (colored water? with sugar?) Matched pairs: have each person run twice (on different days?), one time drinking Gatorade, one time drinking placebo. Randomize order. Matched Pairs: Identical Twins Why not always randomize? Randomized experiments are ideal, but sometimes not ethical or feasible Ethics: Can t force someone to partake in a treatment known or suspected to cause harm Feasibility: Often, randomized experiments are simply not feasible (cost, time, and practical issues are limiting factors) Often, you have to do the best you can with data from observational studies Randomization in Data Collection Was the sample randomly selected? Yes Possible to generalize to the population No Should not generalize to the population Was the explanatory variable randomly assigned? Yes Possible to make conclusions about causality Can not make conclusions about causality No Two Fundamental Questions in Data Collection Population Sample DATA Random sample??? Randomized experiment??? 5

6 Randomization Doing a randomized experiment on a random sample is ideal, but rarely achievable If the focus of the study is using a sample to estimate a value for the entire population, you need a random sample, but do not need a randomized experiment (example: election polling) If the focus of the study is establishing causality from one variable to another, you need a randomized experiment and can settle for a non- random sample (example: clinical trials) Summary Randomized experiments involve randomly determining the level of the explanatory variable Randomized experiments prevent confounding variables, so causality can be inferred A control or comparison group is necessary The placebo effect exists, so a placebo and blinding should be used Matched pair experiments can be useful when the response variable varies a lot from unit to unit To Do Read Section 1.3 HW 1.3 due 10:10am Friday, Jan 30 th 6