Statistics - 1.2

What does it mean when an observational study is​ retrospective?

A retrospective study requires that individuals look back in time or require the researcher to look at existing records.

Forty patients with skin cancer are divided into two groups. One group receives an experimental drug to fight cancer comma the other a placebo. After two years comma the spread of the cancer is measured. Does the description correspond to an observational study or an​ experiment?

The study is an experiment because the researchers control one variable to determine the effect on the response variable.

Determine whether the study depicts an observational study or an experiment. First-grade students are randomly divided into two groups. One group is given a fruit and vegetable for lunch; the other is given candy for lunch. After lunch, each group is given an attention test to compare hyperactivity.

The study is an experiment because the researchers control one variable to determine the effect on the response variable.

What does it mean when an observational study is​ prospective?

A prospective study collects the data over time.

What is a designed​ experiment?

A designed experiment is when a researcher assigns individuals to a certain​ group, intentionally changing the value of an explanatory​ variable, and then recording the value of the response variable for each group.

What is a lurking​ variable?

A lurking variable is an explanatory variable that was not considered in a​ study, but that affects the value of the response variable in the study. In​ addition, lurking variables are typically related to explanatory variables in the study. A relation that appears to exist between a certain explanatory variable and the response variable may be due to some other variable or variables not accounted for in the study. These variables are called lurking variables.

What is an observational​ study?

An observational study measures the value of the response variable without attempting to influence the value of either the response or explanatory variables.

What is a​ case-control study?

Case-control studies are observational studies that 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. A disadvantage to this type of study is that it requires individuals to recall information from the past. Plus it requires the individuals to be truthful in their responses. An advantage of​ case-control studies is that they are relatively inexpensive to conduct and can be done relatively quickly.

What is meant by​ confounding?

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 study. Confounding is potentially a major problem with observational studies.​ Often, the cause of confounding is a lurking variable.

Which is the superior observational​ study? Why?

Neither study is always the superior to the other. Both have advantages and disadvantages that depend on the situation. Both studies are inexpensive and can be done relatively quickly. A​ case-control study is limited in that it requires individuals to recall information​ correctly, and to answer questions truthfully. A​ cross-sectional study is limited in that it only gives information at a specific point in time or over a very short period of​ time, and might not contain valuable information that occurs outside of that point in time.

What is a confounding​ variable?

A confounding variable is an explanatory variable that was considered in a study whose effect cannot be distinguished from a second explanatory variable in the study. The big difference between lurking variables and confounding variables is that lurking variables are not considered in the study whereas confounding variables are measured in the study.

What is a​ cross-sectional study?

​Cross-sectional studies are observational studies that collect information about individuals at a specific point in time or over a very short period of time. For​ example, a researcher might want to assess the risk associated with smoking by looking at a group of​ people, determining how many are smokers and comparing the incidence rate of lung cancer of the smokers to the nonsmokers. A clear advantage of​ cross-sectional studies is that they are cheap and quick to do.​ However, cross-sectional studies have limitations. For the lung cancer​ study, it could be that individuals develop cancer after the data are​ collected, so the study will not give the full picture.