Figure 2: Sagittal abdominal diameter (SAD) measurement and
Inter-observer agreement
(a) Vertical white arrow shows sagittal abdominal diameter (SAD)
measurement: the largest skin-to-skin distance perpendicular to the
table. Arrowhead (yellow) indicates anatomical landmarks for each
location: the umbilicus, the left emerging renal vein, and the emerging
inferior mesenteric artery.
(b) SAD values of observer A vs observer B for each corresponding
measurement. The continuous line of equality (y=x) represents perfect
concordance. The discontinuous line represents the relationship between
the 2 readings. Umbilical SAD measurements are the most similar to the
line of equality. In the left renal vein and inferior mesenteric artery
measurements, the lines are almost parallel to the reference line,
indicating a possible systematic error.
(c) Bland-Altman plots to compare agreement. Difference between the two
measurements: the continuous line represents perfect agreement (Obs. A −
Obs. B = 0). The discontinuous line represents the mean difference
between the 2 readings. The grey area defines the limits of agreement
(95% confidence interval). The agreement was best for umbilical
measurements as they are closest to the reference line. For the other
SAD measurements, several readings were outside the limits of agreement.
Systematic bias was ruled out since perfect agreement (y=0) was within
the confidence interval.