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Observational Studies

Observational Studies. Main ideas: 1- What is an observational study? 2- How are subjects selected? 3- What is a parameter of interest? 4- What is the nature and scope of the conclusion?. Observational studies – the population is observed without any interference by the investigator.

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Observational Studies

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  1. Observational Studies

  2. Main ideas: 1- What is an observational study? 2- How are subjects selected? 3- What is a parameter of interest? 4- What is the nature and scope of the conclusion?

  3. Observational studies – the population is observed without any interference by the investigator Experimental studies – the investigator tries to control the environment in which the hypothesis is tested (the randomized, double-blind clinical trial is the gold standard) Observational vs. Experimental Studies

  4. Observational Studies: 1- Looking at a current or past situation 2- Collect relevant data of that situation by observation. a- collecting from past event – Retrospective has already happened b- collecting from current event – Prospective watching while it happens 3- Conclusions Poll 1.2

  5. Observational Studies: 3- Conclusions a- because not an SRS cannot draw conclusions about the population. b- No Causation – just an association 4- Watch out for Lurking Variables. Lurking Variables – affect the explanatory and response variables (some other reason than the one thought up that might cause the same effects) Poll 1.3

  6. Coffee Chronicles BYMELISSA AUGUST, ANN MARIE BONARDI, VAL CASTRONOVO, MATTHEW JOE'S BLOWS Last week researchers reported that coffee might help prevent Parkinson's disease. So is the caffeine bean good for you or not? Over the years, studies haven't exactly been clear:

  7. According to scientists, too much coffee may cause... • 1986 --phobias, --panic attacks • 1990 --heart attacks, --stress, --osteoporosis • 1991 -underweight babies, --hypertension • 1992 --higher cholesterol • 1993, 08 --miscarriages • 1994 --intensified stress • 1995 --delayed conception But scientists say coffee also may help prevent... • 1988 --asthma • 1990 --colon and rectal cancer,... • 2004—Type II Diabetes (*6 cups per day!) • 2006—alcohol-induced liver damage • 2007—skin cancer

  8. Limitation of observational research: confounding • Confounding: risk factors don’t happen in isolation, except in a controlled experiment. • Example:In a case-control study of a salmonella outbreak, tomatoes were identified as the source of the infection. But the association was spurious. Tomatoes are often eaten with serrano and jalapeno peppers, which turned out to be the true source of infection. • Example:Breastfeeding has been linked to higher IQ in infants, but the association could be due to confounding by socioeconomic status. Women who breastfeed tend to be better educated and have better prenatal care, which may explain the higher IQ in their infants.

  9. Why Observational Studies? • Cheaper • Faster • Can examine long-term effects • Hypothesis-generating • Sometimes, experimental studies are not ethical (e.g., randomizing subjects to smoke)

  10. Among a group of disabled women aged 65 and older who were tracked for several years, those who had a vitamin B12 deficiency were twice as likely to suffer severe depression as those who did not. (American Journal of Psychiatry 157 [2000]: 715) 1- Retrospective or Prospective? Poll 1.4 2- Subjects and how they were selected? 3- What is the parameter of interest? Poll 1.5 4- Nature & scope of conclusion the study can reach? Poll 1.6

  11. Researchers have linked an increase in the incidence of breast cancer in Italy to dioxin released by an industrial accident in 1976. The study identified 981 women who lived near the site of the accident and were under age 40 at the time. Fifteen of the women had developed breast cancer at an unusually young average age of 45. Medical records showed that they had heightened concentrations of dioxin in their blood and that each tenfold increase in dioxin level was associated with a doubling of the risk of breast cancer. (Science News, Aug. 3, 2002) 1- Retrospective or Prospective? Poll 1.7 2- Subjects and how they were selected? 3- What is the parameter of interest? Poll 1.8 4- Nature & scope of conclusion the study can reach? Poll 1.9

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