A group of investigators plans to conduct a study to assess the relationship between colon cancer and elevated plasma C-reactive protein (CRP) levels. The study design involves determining the prevalence of elevated plasma CRP levels (based on prespecified cutoff values) and of colon cancer in a sample of individuals at a given point in time. The prevalence of elevated CRP levels is compared between patients with and without colon cancer. Which of the following is the best statement of the null hypothesis for this study?

Question

A group of investigators plans to conduct a study to assess the relationship between colon cancer and elevated plasma C-reactive protein (CRP) levels.  The study design involves determining the prevalence of elevated plasma CRP levels (based on prespecified cutoff values) and of colon cancer in a sample of individuals at a given point in time.  The prevalence of elevated CRP levels is compared between patients with and without colon cancer.  Which of the following is the best statement of the null hypothesis for this study?

Quizplus · Accepted Answer

To state the null hypothesis correctly, the study design must be considered. In this case, the study is cross-sectional as the investigators are taking a snapshot of a sample and measuring prevalence of elevated C-reactive protein (CRP) levels and of colon cancer at the same time. Therefore, the null hypothesis should state that there is no association between elevated plasma CRP levels (equivalent to exposure) and colon cancer (equivalent to outcome). In general, the null hypothesis represents a statement of no association between variables of interest. As this is a cross-sectional study, the temporal relationship between the 2 variables (ie, whether the exposure preceded the outcome, or whether the outcome preceded the exposure) cannot be determined. It would not be suitable for the null hypothesis in this case to suggest a temporality or risk profile, whether having colon cancer is a risk factor impacting CRP levels (Choice B) or having elevated CRP levels is a risk factor for colon cancer (Choice C). (Choice A) This would not be a suitable null hypothesis as it states that there is an association ("more prevalent") between an exposure and outcome. (Choice D) This would have been a valid statement of the null hypothesis for a cohort study, in which individuals with and without elevated CRP levels are followed over time to determine the risk of colon cancer. Educational objective: The null hypothesis is the statement of no relationship between the exposure and the outcome. To state the null hypothesis correctly, the study design should be considered.

A Group of Investigators Plans to Conduct a Study to Assess