Left atrial pressure may be estimated using pulmonary capillary wedge pressure (PCWP) measurements; the typical range is 6-12 mm Hg, and recorded values are whole numbers. Over the course of two hours, a patient in the critical care unit has 20 serial PCWP measures collected. The maximum recorded value among these 20 observations is 12 mm Hg, while the minimum recorded value is 10 mm Hg. Which of the following is most likely to remain unaltered if the next measurement is 26 mm Hg?

Question

Quizplus · Accepted Answer

Eductional Objective: An outlier is a value that is extreme and unusual in a dataset. It might be due to a recording error, a measuring error, or a natural occurrence. The figure of 26 mm Hg is an anomaly in this situation, as all of the other results range between 10 and 12 mm Hg. An outlier can have an impact on both measures of central tendency (mean, median, mode) and measures of dispersion (standard deviation, variance). 
This patient's first values ranged between 10 and 12 mm Hg. Although a numerical example is not necessary to accurately answer this question, it might assist to clarify the effect of an outlier such as 26 mm Hg. Assume that the patient's initial 20 readings were as follows: 9 of 10 mm Hg, 6 of 11 mm Hg, and 5 of 12 mm Hg. The mode is the most often recorded data point, hence 10 mm Hg is the mode for this initial collection (because this value is observed 9 times whereas the other 2 values are observed 6 times and 5 times). 
If the next measurement is 26 mm Hg, the mode would remain 10 mm Hg because this would still be the most commonly observed value. Therefore, the mode would remain unchanged. The mode tends to be resistant to outliers because outliers are not likely to affect the most frequently observed value in a dataset.

Left Atrial Pressure May Be Estimated Using Pulmonary Capillary Wedge