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Difficulty: EasyInferential Statistical Tests

A quality improvement committee at a large hospital evaluates two different preoperative skin preparation protocols. Eight hundred patients undergoing elective abdominal surgery are randomized to receive either a chlorhexidine-alcohol scrub (n=400) or a povidone-iodine scrub (n=400). The researchers track the patients for 30 days postoperatively to determine the presence or absence of a surgical site infection. The primary outcome is the proportion of patients in each group who develop an infection. Which of the following is the most appropriate statistical test to compare the primary outcome between these two study groups?

  1. Chi-square testAnswer
  2. B
    Two-sample t-test
  3. C
    Analysis of variance
  4. D
    Paired t-test
  5. E
    Pearson correlation coefficient

Answer

Chi-square test
The correct statistical test is the Chi-square test. In this study, the researchers are comparing two independent groups (chlorhexidine-alcohol vs. povidone-iodine) based on a categorical, binary outcome (presence vs. absence of a surgical site infection). When evaluating the association between two categorical variables, particularly comparing proportions or frequencies between independent groups with an adequate sample size, the Chi-square test is the appropriate choice.

Step-by-Step Solution

1
Identify the independent variable and its data type.
The independent variable is the skin preparation protocol (chlorhexidine vs. povidone-iodine), which is a categorical (nominal) variable with two independent groups.
Determining the predictor variable type is the first step in selecting a statistical test.
2
Identify the dependent variable and its data type.
The dependent variable is the development of a surgical site infection (yes vs. no), which is a categorical (binary/nominal) variable.
The outcome variable's data type dictates the mathematical approach used to analyze differences.
3
Select the statistical test that compares a categorical outcome between independent categorical groups.
The Chi-square test is selected.
The Chi-square test is designed to compare proportions (frequencies) of a categorical outcome across two or more independent groups.

Key Concept

Inferential Statistical Tests - Test Selection
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Topics

Inferential Statistical Tests

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