Dexcom G5 User Manual page 279

Accuracy Relative to YSI
Accuracy between matched pairs was also estimated by calculating the
percent difference between the system reading and the YSI value. For
example, if the YSI value is 100 mg/dL and the system reading is 90 mg/dL, a
10% difference between the system and the YSI is reported. The system and
YSI values were compared by pairing the system reading that fell immediately
after the YSI value was collected.
In the example above, the system reading is less than the YSI value, so the
percent difference reading is negative. The mean percent difference is the
average of all positive and negative percent differences between the two
devices; it tells you if the system reads higher or lower on average than the
YSI within each glucose range.
Another estimate used to show the accuracy of the system is the absolute
percent difference. The absolute percent difference tells you the percent
difference or "distance" between the system and YSI values, but does not tell
you whether the system is reading, on average, higher or lower than the YSI
laboratory standard. The mean absolute percent difference is the average
"distance" (regardless if positive or negative) between system readings and
YSI values.
Accuracy measures in differences for both the Original Adult and Software
505 Adult Studies are summarized in Table 4-A. Accuracy measures in
differences for both the Original Pediatric and Software 505 Pediatric Studies
are summarized in Table 4-B. Table 4-A and 4-B are categorized within CGM
glucose ranges.
For example, in the Software 505 Adult Study (Table 4-A), overall, on
average, the system reads 2.5% different (Mean Percent Difference) than the
reference and 9.0% absolute different (Mean Absolute Difference) than the
reference values. The Median Percent Difference shows that half of the time
the system reads 2.4% or less than the YSI BG values and the Median
Absolute Percent Difference shows that half of the time the system reads
about 7.0% or less than the YSI BG values.
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Dexcom G5 Mobile System User Guide
Technical Information