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Original ArticleOpen Access
An Estimation of Deviation Towards the Mean for Serum Lipid Fractions in Patients Followed for a Varied Duration
Yipintsoi T 
,
Yipintsoi S
,
Yipintsoi S We evaluated the deviation towards the mean and attempted to quantify it among the different
lipid fractions in patients. The study was done retrospectively on patients who were judged
to be metabolically stable and had repeated total cholesterol (TC), high density lipoprotein
cholesterol (HDL) and triglyceride (TG) measured in a single laboratory with known coefficient
of variation for repeated measurements. The patients and their data were separated into 3
groups. Group A (56 patients) evaluated the difference between the first and its average obtained
from an average of 4 samples per patient within a mean of 9 months. Group B, examined pairs of
data taken an average of 12 months apart. Group C, evaluated 45 patients with at least 3 data points
each a year apart. Linear correlations were applied for the repeats versus the first samples. Highly
significant correlations were obtained for all the groups. The slopes were less than one (generally
between 0.66 and 0.85) and intercepts had positive values. This was seen even for the HDL whose
range of values span 25 to 85 mg per cent. These results strongly supported deviation towards
the mean such that from our calculation and in this population, a person with an initial TC of
200 mg per cent would have from 37 to 61 per cent chance of obtaining a significantly higher value
if the test was repeated. The magnitude of the change would average 30 mg per cent for cholesterol
and as much as 30 per cent of the initial values for TG. In this evaluation, the time intervals
between repeats did not appear to influence the result. Yearly follow-ups also did not seem to
exhibit the effect of aging. However, the latter 2 conclusions rested on a small number of observations.
It is suggested that several repeated estimations of these lipid fractions be done before
a decision is made towards intervening. In instances of epidemiological studies, it is imperative
to obtain representative repeated measurements since this deviation towards the mean will alter
the slope of the events versus the lipid-variables.
Key word : Total Cholesterol, Triglyceride, High Density Lipoprotein, Repeated Sampling
lipid fractions in patients. The study was done retrospectively on patients who were judged
to be metabolically stable and had repeated total cholesterol (TC), high density lipoprotein
cholesterol (HDL) and triglyceride (TG) measured in a single laboratory with known coefficient
of variation for repeated measurements. The patients and their data were separated into 3
groups. Group A (56 patients) evaluated the difference between the first and its average obtained
from an average of 4 samples per patient within a mean of 9 months. Group B, examined pairs of
data taken an average of 12 months apart. Group C, evaluated 45 patients with at least 3 data points
each a year apart. Linear correlations were applied for the repeats versus the first samples. Highly
significant correlations were obtained for all the groups. The slopes were less than one (generally
between 0.66 and 0.85) and intercepts had positive values. This was seen even for the HDL whose
range of values span 25 to 85 mg per cent. These results strongly supported deviation towards
the mean such that from our calculation and in this population, a person with an initial TC of
200 mg per cent would have from 37 to 61 per cent chance of obtaining a significantly higher value
if the test was repeated. The magnitude of the change would average 30 mg per cent for cholesterol
and as much as 30 per cent of the initial values for TG. In this evaluation, the time intervals
between repeats did not appear to influence the result. Yearly follow-ups also did not seem to
exhibit the effect of aging. However, the latter 2 conclusions rested on a small number of observations.
It is suggested that several repeated estimations of these lipid fractions be done before
a decision is made towards intervening. In instances of epidemiological studies, it is imperative
to obtain representative repeated measurements since this deviation towards the mean will alter
the slope of the events versus the lipid-variables.
Key word : Total Cholesterol, Triglyceride, High Density Lipoprotein, Repeated Sampling
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