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Rationale of the Week | JR asks you; What is the Coefficient of Variation?

For last week’s practice question, we quizzed test takers on the coefficient of variation. 85% of respondents chose the best answer. We want to share this important updated information, so you can pass it on to people living with diabetes and your colleagues, plus prepare for exam success!

Before we start though, if you don’t want any spoilers and haven’t tried the question yet, you can answer below: Answer Question

Question: You are reviewing an ambulatory glucose profile with JR, a 27-year-old on an insulin pump.  Time in range is 59% and the coefficient of variation is 46%.  JR asks you to explain the coefficient of variation. What is the most helpful response?

Answer Choices:

  • The amount of time blood glucose is at least one standard deviation below target.
  • A statistic that summarizes if you are taking sufficient daily insulin based on basal rates.
  • Great question that we can address later. Let’s focus on improving time in range first.
  • It reflects how much your glucose levels fluctuate above and below target range.

As shown above, the most common choice was option 4, the second most common answer was option 1, then option 2, and then finally option 3.

Getting to the Best Answer

Answer 1 is incorrect. 7.13% chose this answer, “The amount of time blood glucose is at least one standard deviation below target.” This is a juicy answer and is tempting. However, the coefficient of variation isn’t looking at only the below target blood glucose levels. It reflects how much glucose levels fluctuate above and below target range.

Answer 2 is incorrect. 6.31% of you chose this answer, “A statistic that summarizes if you are taking sufficient daily insulin based on basal rates.” Basal insulin dosing can affect glucose levels over night and between meals. But both the basal and bolus insulin affect the coefficient of variation which reflects how much the glucose levels are fluctuating above and below target range.

Answer 3 is incorrect. 1.63% of respondents chose this answer, “Great question that we can address later. Let’s focus on improving time in range first.” Time in range is important to discuss, however when using a person centered approach, we start with the topic that is most important to the person first.

Finally, Answer 4 is correct. 84.93% chose this answer, “It reflects how much your glucose levels fluctuate above and below target range.” GREAT JOB. 85% of you chose the best answer. When looking at the Ambulatory Glucose Profile, the shaded area reveals how much the glucose is fluctuating above and below target range. The goal for coefficient of variation (CV) is less than 36%, which is associated with a higher percentage of time in range.

CV is a fancy term for a simple calculation: dividing the SD by the mean glucose and multiplying by 100 to get a percentage. For example, if the SD is 50 mg/dl, and the average glucose is 150 mg/dl, then you divide 50 by 150, multiply by 100, and you get a CV of 33%.

Why use CV instead of SD? SD is highly influenced by the mean glucose – someone with a higher mean glucose will have a higher SD. This division helps “correct” and normalize glucose variability, allowing for a single variability goal (less than 36%) that applies to people with different mean glucose levels.

We hope you appreciate this week’s rationale! Thank you so much for taking the time to answer our Question of the Week and participate in this important learning activity!


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