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Regression Toward the Mean01:52

Regression Toward the Mean

Regression toward the mean (“RTM”) is a phenomenon in which extremely high or low values—for example, and individual’s blood pressure at a particular moment—appear closer to a group’s average upon remeasuring. Although this statistical peculiarity is the result of random error and chance, it has been problematic across various medical, scientific, financial and psychological applications. In particular, RTM, if not taken into account, can interfere when researchers try to extrapolate results...
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z scores are the standardized values obtained after converting a normal distribution into a standard normal distribution. A z score is measured in units of the standard deviation. The z score tells you how many standard deviations the value x is above (to the right of) or below (to the left of) the mean, μ. Values of x that are larger than the mean have positive z scores, and values of x that are smaller than the mean have negative z scores. If x equals the mean, then x has a z score of zero.
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Constructing normalcy and discrepancy indexes for birth weight and gestational age using a threshold regression

G A Whitmore1, Guangyu Zhang, Mei-Ling Ting Lee

  • 1McGill University, Montreal, Canada.

Biometrics
|August 16, 2011
PubMed
Summary

New indexes, the birth normalcy index (BNI) and birth discrepancy index (BDI), precisely assess newborn health by analyzing birth weight and gestational age. These tools help researchers better understand birth outcomes and compare populations.

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Area of Science:

  • Perinatal health
  • Biostatistics
  • Maternal and child health

Background:

  • Birth weight and gestational age are key newborn health indicators.
  • These measures are correlated but can be inconsistent.
  • Existing measures lack precision in indicating healthy birth outcomes.

Purpose of the Study:

  • To develop summary indexes for birth weight and gestational age.
  • To provide more precise indications of newborn health status.
  • To aid health researchers in analyzing birth outcomes.

Main Methods:

  • Introduction of the birth normalcy index (BNI) and birth discrepancy index (BDI).
  • BNI and BDI are functions of birth weight and gestational age, orthogonal in logarithmic form.
  • BNI modeled using a three-component mixture of inverse Gaussian distributions; BDI modeled using a noncentral t-distribution.

Main Results:

  • BNI quantifies the normality of the birth weight-gestational age combination.
  • BDI assesses the consistency between birth weight and gestational age.
  • Proposed z-scores and t-scores for comparing birth outcomes across populations.

Conclusions:

  • BNI and BDI offer improved precision for assessing newborn health.
  • These indexes facilitate comparisons of birth outcomes in diverse reference populations.
  • Distributions of BNI and BDI can be estimated using threshold regression.