Warm Up Categorize each variable based on its level of measurement as nominal, ordinal, interval, or ratio.

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1 Warm Up Categorize each variable based on its level of measurement as nominal, ordinal, interval, or ratio. gender IQ distance commuting pain rating 1 10 Warm Up Solve: 1

2 An observational study measures the characteristics of a population by studying individuals in a sample, but does not attempt to manipulate or influence the variables of interest. The easiest examples of observational studies are surveys. No attempt is made to influence anything just ask questions and record the responses. A designed experiment applies a treatment to individuals (referred to as experimental units or subjects) and attempts to isolate the effects of the treatment on a response variable. They try to determine what affect a particular treatment has on an outcome. After reading the article carefully, try to decide whether it was anobservational study or a designed experiment. Vietnam veterans who experienced posttraumatic stress disorder (PTSD) were twice as likely to die from heart disease as veterans without PTSD, a new Geisinger study finds. In a study published in the July issue of Psychosomatic Medicine, Geisinger Senior Investigator Joseph Boscarino, PhD, MPH examined the prevalence of heart disease, PTSD and other problems in more than 4,000 Vietnam veterans. The more severe the PTSD diagnosis, the greater the likelihood of death from heart disease, the study showed. Vietnam veterans with PTSD like chronic smokers are at higher risk of early death from heart disease, Dr. Boscarino concluded. Boscarino equated PTSD to smoking two to three packs of cigarettes per day for more than 20 years. PTSD causes the body to release stress hormones, which leads to the inflammation and damage to the arteries and cardiovascular system damage. Stress hormones also tend to reduce the amount of inflammation reducing cortisol in the body though researchers aren't sure why. "Increased levels of stress hormones and less cortisol from PTSD are a bad combination," Dr. Boscarino explained. "Basically, PTSD just cooks your arteries in this situation." Dr. Boscarino previously found that people with PTSD had dramatically higher rates of chronic health problems such as psoriasis, arthritis and other inflammatory diseases. "The science is conclusively showing that if you suffer psychological trauma, it's going to take a toll on your physical health," Dr. Boscarino said. "Getting counseling today is critical to avoiding a related problem tomorrow." This study excluded patients with a prior history of heart disease and included a national sample of veterans, which is different from prior studies on the topic, Boscarino said. Geisinger Health System. "PTSD Causes Early Death From Heart Disease, Study Suggests." ScienceDaily. ScienceDaily, 8 July < 2

3 After reading the article carefully, try to decide whether it was anobservational study or a designed experiment. Weight Loss with a Low Carbohydrate, Mediterranean, or Low Fat Diet BACKGROUND Trials comparing the effectiveness and safety of weight loss diets are frequently limited by short follow up times and high dropout rates. METHODS In this 2 year trial, we randomly assigned 322 moderately obese subjects (mean age, 52 years; mean body mass index [the weight in kilograms divided by the square of the height in meters], 31; male sex, 86%) to one of three diets: low fat, restricted calorie; Mediterranean, restricted calorie; or low carbohydrate, non restricted calorie. RESULTS The rate of adherence to a study diet was 95.4% at 1 year and 84.6% at 2 years. The Mediterranean diet group consumed the largest amounts of dietary fiber and had the highest ratio of monounsaturated to saturated fat (P<0.05 for all comparisons among treatment groups). The lowcarbohydrate group consumed the smallest amount of carbohydrates and the largest amounts of fat, protein, and cholesterol and had the highest percentage of participants with detectable urinary ketones (P<0.05 for all comparisons among treatment groups). The mean weight loss was 2.9 kg for the low fat group, 4.4 kg for the Mediterranean diet group, and 4.7 kg for the low carbohydrate group (P<0.001 for the interaction between diet group and time); among the 272 participants who completed the intervention, the mean weight losses were 3.3 kg, 4.6 kg, and 5.5 kg, respectively. The relative reduction in the ratio of total cholesterol to high density lipoprotein cholesterol was 20% in the low carbohydrate group and 12% in the low fat group (P=0.01). Among the 36 subjects with diabetes, changes in fasting plasma glucose and insulin levels were more favorable among those assigned to the Mediterranean diet than among those assigned to the low fat diet (P<0.001 for the interaction among diabetes and Mediterranean diet and time with respect to fasting glucose levels). CONCLUSIONS Mediterranean and low carbohydrate diets may be effective alternatives to low fat diets. The more favorable effects on lipids (with the lowcarbohydrate diet) and on glycemic control (with the Mediterranean diet) suggest that personal preferences and metabolic considerations might inform individualized tailoring of dietary interventions. (ClinicalTrials.gov number, NCT ) Probably the biggest difference between observational studies and designed experiments is the issue of association versus causation. Since observational studies don't control any variables, the results can only be associations. Because variables are controlled in a designed experiment, we can have conclusions of causation. 3

4 Observational studies only allow us to claim association,not causation. The primary reason behind this is something called a lurking variable (sometimes also termed a confounding factor). A lurking variable is a variable that affects both of the variables of interest, but is either not known or is not acknowledged. Example 1 of Lurking Variables What mistaken assumption is the boy making? What is the Lurking variable? 4

5 Example 2 of Lurking Variables A well known relationship exists between shark attacks and ice cream sales: both of them increase at the same time. This relationship is often used to demonstrate how two seemingly unrelated events can often vary together, which requires those who notice the correlation to consider what lurking variables might be in effect. How might you explain this correlation? Important Observational studies only allow us to claim association,not causation. So, why use observational studies? A designed experiment trial may be impossible, impractical or unethical. Observational studies may cost much less than designed experiments possible to get data from more people 5

6 1. Cross sectional Studies 2. Case control Studies 3. Cohort Studies 1. Cross sectional Studies This first type of observational study involves collecting data about individuals at a certain point in time. A researcher concerned about the effect of working with asbestos might compare the cancer rate of those who work with asbestos versus those who do not. Example: A cross sectional study can be used to look at the association between obesity and television watching. A sample of people from the population that you are interested in can be polled and asked about their height/weight ratio and the number of hours of television the person watches each week. 6

7 2. Case control Studies These studies are retrospective, meaning that they require individuals to look back in time or require the researcher to look at existing records. In case control studies, individuals that have a certain characteristic are matched with those that do not. Case control studies are frequently used in the medical community to compare individuals with a particular characteristic with individuals who do not have that characteristic. Researchers attempt to select homogeneous groups, so that on average, all other characteristics of the individuals will be similar, with only the characteristic in question differing. 3. Cohort Studies A cohort study first identifies a group of individuals to participate in the study (the cohort). The cohort is then observed over a period of time (sometimes a long period of time). Over this time period, characteristics about the individuals are recorded and some individuals in the study will be exposed to certain factors (not intentionally) and others will not. At the end of the study the value of the response variable is recorded for the individuals 7

8 A recent article in the BBC News Health section described a study concerning dementia and "mid life ills". According to the article, researches followed more than 11,000 people over a period of years. They found that smoking, diabetes, and high blood pressure were all factors in the onset of dementia. In 2004, researchers published an article in the New England Journal of Medicine regarding the relationship between the mental health of soldiers exposed to combat stress. The study collected information from soldiers in four combat infantry units either before their deployment to Iraq or three to four months after their return from combat duty. In 1993, the National Institute of Environmental Health Sciences funded astudy in Iowa regarding the possible relationship between radon levels and the incidence of cancer. The study gathered information from 413 participants who had developed lung cancer and compared those results with 614 participants who did not have lung cancer. Cohort Study Cross sectional Study Case control Study 8