Section 1.2 Observational Studies Vs. Designed Experiments
¶Definition 1.2.1. response variable.
The response variable is the focus of a question in a study or experiment.Definition 1.2.2. explanatory variable.
An explanatory variable is one that explains changes in the response variable.Definition 1.2.3. observational study.
measuring response variable without influencing the values of either the response variable or explanatory variableDefinition 1.2.4. cross-sectional studies.
observational studies that collect data at one particular timeDefinition 1.2.5. case-control studies.
observational studies that require individuals to look back in time to record measurements (retrospective)Definition 1.2.6. cohort studies.
observational studies that track individuals repeatedly over time (prospective)Definition 1.2.7. designed experiment.
measuring response variable after intentionally changing the value of the explanatory variableDefinition 1.2.8. confounding.
in a study occurs when the effects of two or more explanatory variables are not separated. Therefore, any relation that may exist between an explanatory variable and the response variable may be due to some other variable or variables not accounted for in the studyDefinition 1.2.9. lurking variable.
a variable that was not considered in the study, but affects the response variableIMPORTANT: Because of the possibility of lurking variables, observational studies DO NOT allow a researcher to claim causation, only association.
Definition 1.2.10. confounding variable.
a variable in the study where you can’t tell the difference between its effect and another explanatory variable’s effectDefinition 1.2.11. census.
list of information from all individuals in a populationReading Questions Observational Study or Designed Experiment?
1.
Rats with cancer are divided into two groups. One group receives 5 milligrams of a medication that is thought to fight cancer, and the other receives 10 milligrams. After 2 years, the spread of cancer is measured. Answer2.
Conservation agents netted 250 large-mouth bass in a lake and determined how many were carrying parasites. Answer3.
Seventh grade students are randomly divided into two groups. One group is taught math using traditional techniques; the other is taught math using a reform method. After 1 year, each group is given an achievement test to compare proficiency. Answer4.
A survey was conducted asking 400 people, "Do you prefer Coke or Pepsi?" AnswerReading Questions Daily Coffee Consumption
Is there an association between daily coffee consumption and the occurrence of skin cancer? Researchers asked 93,676 women to disclose their coffee drinking habits and also determined which of the women had non-melanoma skin cancer. The researchers concluded that consumption of 6 or more cups of caffeinated coffee per day was associated with a reduction in non-melanoma skin cancer.
1.
Was this an observational study or experiment? If observational, what type of observational study was it? Answer2.
What is the response variable? What is the explanatory variable? Answer3.
Can we conclude drinking six or more cups of coffee reduces the chance of non-melanoma skin cancer? AnswerReading Questions Get Married, Gain Weight
Are young couples who marry or cohabit more likely to gain weight than those who stay single? Researchers followed 8000 men and women for 7 years. At the start of the study, none of the participants were married or living with a romantic partner. The researchers found that women who married or cohabited during the study period gained 9 pounds more then single women, and married or cohabiting men gained, on average, 6 pounds more than single men.