Biology Reference
In-Depth Information
section introduces the sample asymmetry (SA), a measure possessing
these desired properties.
2
E
XERCISE
6-1
Describe why the mean value does not represent a good measure for
assessing the variability of the RRI series.
E
XERCISE
6-2
Give examples of two data sets having equal SDs, one corresponding to
a RRI series with transient decelerations and the other to one with
transient accelerations.
VI. TIME-INDEPENDENT MEASURES: SAMPLE
ASYMMETRY OF A RANDOM VARIABLE
We design the new SA measure to comply with the following conditions:
1. SA should grow when there are more decelerations in the RRI
sequence;
2. SA should decrease as there are more accelerations in the RRI
sequence;
3. SA should take positive values; and
4. SA
¼
1 for perfectly symmetric distributions of the RRI sequence.
Conditions 3 and 4 are of a technical nature and are, in essence,
conditions of calibration. In contrast, conditions 1 and 2 are essential for
constructing a measure overcoming the limitations of SD and skewness
as measures for reduced HRV and transient decelerations.
Conditions 1 and 2 suggest that SA may be defined in the form of a ratio
R
2
R
1
where the numerator R
2
is a measure for the magnitude of RRI
decelerations and the denominator R
1
measures the magnitude of
RR accelerations. Condition 4 will then mean R
1
¼
SA
¼
R
2
, that is, the
magnitudes of accelerations and decelerations in the RRI sequence are
the same, exactly as one would expect from a symmetric distribution.
Thus, we focus on designing R
1
and R
2
.
2. This measure was first introduced by Kovatchev et al. (2003).
