Glycine (Gly) has been implicated in several neurological disorders, including malignant brain tumors. However, the precise measurement of Gly has been difficult, primarily due to the spectral overlap with myo-inositol (mI). A novel approach to measuring Gly and mI in healthy and tumorous human brains provides more reliable spectral differentiation between Gly and mI, such that alterations of Gly in brain tumors can now be evaluated more precisely. A group of researchers plans to conduct 2 parallel studies to measure and compare Gly levels among healthy and tumorous brains. Study A will use the current approach to measure Gly in the brain, whereas study B will use the novel approach. All other factors being equal, which of the following statements is most likely true concerning these 2 studies?
A)Compared to study A, study B will have a higher probability of establishing a difference in Gly that does not exist between groups
B)Differences in Gly levels between groups in study A will be statistically different from the differences in Gly levels between groups in study B
C)Study B will have a higher probability of establishing a true difference in Gly between groups than study A
D)The confidence interval for the difference in Gly levels among healthy and tumorous brains will most likely include the null value in study A
E)The difference in Gly levels among healthy and tumorous brains will be statistically significant only in study B

Question

Glycine (Gly) has been implicated in several neurological disorders, including malignant brain tumors.  However, the precise measurement of Gly has been difficult, primarily due to the spectral overlap with myo-inositol (mI).  A novel approach to measuring Gly and mI in healthy and tumorous human brains provides more reliable spectral differentiation between Gly and mI, such that alterations of Gly in brain tumors can now be evaluated more precisely.  A group of researchers plans to conduct 2 parallel studies to measure and compare Gly levels among healthy and tumorous brains.  Study A will use the current approach to measure Gly in the brain, whereas study B will use the novel approach.  All other factors being equal, which of the following statements is most likely true concerning these 2 studies?
A)Compared to study A, study B will have a higher probability of establishing a difference in Gly that does not exist between groups
B)Differences in Gly levels between groups in study A will be statistically different from the differences in Gly levels between groups in study B
C)Study B will have a higher probability of establishing a true difference in Gly between groups than study A
D)The confidence interval for the difference in Gly levels among healthy and tumorous brains will most likely include the null value in study A
E)The difference in Gly levels among healthy and tumorous brains will be statistically significant only in study B

Quizplus · Accepted Answer

Explanation: The novel approach to measuring Glycine (Gly) and myo-inositol (mI) in healthy and tumorous brains provides more precise detection of Gly in brain tumors, which reduces the variability in measurement of Gly levels. The lower the measurement variability of an outcome (eg, Gly levels), the more likely a statistical test will detect an effect (eg, difference in Gly levels between healthy and tumorous brains)-an increase in statistical power (ie, a study's ability to detect a true difference, given by [1 - β]). Study B has increased its statistical power by reducing the variability in Gly measurements (more precise detection of Gly). Therefore, compared to study A, study B will have a higher probability of detecting a true difference in Gly between healthy and tumorous brains if such a difference exists (Choice A). (Choices B and E) The increased statistical power in study B increased its ability to detect a difference between groups if one exists; however, the observed difference in study B may or may not be statistically significant, and it may or may not be different from the observed difference in study A. (Choice D) Although the approach used in study A to measure Gly is not as precise as the novel approach used in study B, the observed difference in Gly levels between healthy and tumorous brains in study A may or may not be statistically significant (ie, confidence interval may or may not exclude the null value) depending on other factors such as sample size (n), significance level (α), and effect size (size of the expected difference). Educational objective: The power of a study is the ability to detect the difference between 2 groups (eg, treated versus nontreated, exposed versus nonexposed). Increasing the precision of measurements increases the power of a study.

Glycine (Gly) Has Been Implicated in Several Neurological Disorders, Including