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Review Question - QID 217252

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QID 217252 (Type "217252" in App Search)
A team of researchers is investigating whether differences exist in the incidence of acute kidney injury between obese and non-obese patients who are hospitalized with a respiratory virus infection. With institutional review board approval, the researchers prospectively enroll 450 obese and 1,560 non-obese patients in their study after obtaining informed consent. At hospital admission, each patient receives a serum creatinine measurement. Serum creatinine measurements are repeated daily during the admission. The researchers calculate the change in serum creatinine concentration from admission to hospital day 2 for each patient. The average change is shown for each cohort:

Non-obese cohort: +0.14 mg/dL (95% confidence interval: 0.09-0.20 mg/dL)
Obese cohort: +0.34 mg/dL (95% confidence interval: 0.09-0.54 mg/dL)

Which of the following is true regarding the accuracy and precision of the estimate for average change for the 2 cohorts?

Accuracy cannot be determined but precision was greater in the non-obese cohort.

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Accuracy cannot be determined but precision was greater in the obese cohort.

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Accuracy was greater in the non-obese cohort but precision cannot be determined.

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Accuracy was greater in the obese cohort but precision was greater in the non-obese cohort.

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Both accuracy and precision were greater in the non-obese cohort.

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Accuracy is a measure of how close a measurement is to a known true value whereas precision is a measure of how close a series of measurements are to each other. In this study, accuracy cannot be determined because there is no true value given, but precision was greater in the non-obese cohort, as evidenced by the narrower confidence interval.

The accuracy of a measurement is an evaluation of how closely it reflects a known true value. For example, the accuracy of a diagnostic test can be benchmarked against the existing gold standard test. A diagnostic test that yields results that are concordant with the existing gold standard test 99% of the time is accurate. Put another way, accuracy is determined by whether the confidence interval of a measurement contains the true value. The precision of a measurement is an evaluation of how consistent and reproducible a series of measurements are. Precision is determined by the width of a confidence interval; the narrower the confidence interval, the greater the precision.

Incorrect Answers:
Answer 2: Accuracy cannot be determined but precision was greater in the obese cohort is incorrect because the measurement in the obese cohort had a wider confidence interval, thus denoting lower precision.

Answer 3: Accuracy was greater in the non-obese cohort but precision cannot be determined is incorrect because the information about the precision of these measurements is contained in the width of the confidence intervals. Accuracy cannot be determined because no true value is given.

Answer 4: Accuracy was greater in the obese cohort but precision was greater in the non-obese cohort is incorrect because accuracy cannot be determined in this case since there is no true value given.

Answer 5: Both accuracy and precision were greater in the non-obese cohort is incorrect because accuracy cannot be determined in this case since there is no true value given.

Bullet Summary:
Precision is defined by the consistency and reproducibility of a result and is inversely related to the width of a given confidence interval.

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