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
and
Software 505
Studies are based on 9152 and
2263 paired glucose results, respectively; the data are summarized in Table 4. Table 4 is categorized within
CGM glucose ranges.
Original
Study
(SW10050)
: Overall, on average, the System reads 2.9% different (Mean Percent
Difference) than the reference and 13.3% absolute different (Mean Absolute Difference) than the reference
values. The Median Percent Difference shows that half of the time the System reads 1.7% or less than the
YSI blood glucose values and the Median Absolute Percent Difference shows that half of the time the
System reads about 9.8% or less than the YSI blood glucose values.
Software 505
Study
(SW10505)
: 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 blood glucose values and the Median Absolute Percent Difference shows that half of the time the
System reads about 7.0% or less than the YSI blood glucose values.
