## Chapter 71. Statistics

Which of the following is the outcome variable for a study? Select all that apply.

a. DV

b. IV

c. Confounder

d. Population

Answer a is correct. There are three types of variables: dependent (DV), independent (IV), and confounding. The DV is the response or outcome variable for a study.

Answers b and c are incorrect. The IV is a variable that is manipulated and a confounding variable is any variable that has an effect on the DV over and above the effect of the IV, but is not of specific research interest.

Answer d is incorrect. A population refers to all objects of a similar type in the universe, while a sample is a fraction of the population chosen to be representative of the specific population of interest. Thus, samples are chosen to make generalizations about the population of interest.

A pharmacy resident in South Carolina is charged with evaluating daptomycin as her research project for the year. She is evaluating all patients within 18 months and comparing them to vancomycin. The primary outcome is clinical response as defined by clearance of bacteremia within 5 days. Her data collection sheet has two boxes for the primary outcome (yes and no). What type of measurement scale is the resident collecting?

a. Nominal

b. Ordinal

c. Interval

d. Ratio scales

Answer a is correct. A nominal scale consists of categories that have no implied rank or order (male versus female; or absence versus presence). The patient can fit into only one category; that is, the data points are mutually exclusive.

Answers b, c, and d are incorrect. An ordinal scale has all of the characteristics of a nominal variable; however, the data are placed into rank-ordered categories. Interval scales increase the information provided by an ordinal scale by allowing researchers to quantify a meaningful distance between two units (eg, temperature). Ratio scales differ from interval scales in that they have an absolute zero (eg, blood pressure).

The pharmacy resident in question number 3 completed her study and demonstrated that vancomycin has a higher cure rate of bacteremia at 5 days as compared to daptomycin. She was concerned that she had introduced error into her study because of a low sample size (17 daptomycin patients and 34 vancomycin patients). Additionally, she was concerned that measuring the outcome as yes/no impacted the results. She is going ...

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