In
behavioural genetics
Behavioural genetics, also referred to as behaviour genetics, is a field of scientific research that uses genetic methods to investigate the nature and origins of individual differences in behaviour. While the name "behavioural genetics" ...
, DeFries–Fulker (DF) regression, also sometimes called DeFries–Fulker extremes analysis, is a type of
multiple regression analysis
In statistical modeling, regression analysis is a set of statistical processes for estimating the relationships between a dependent variable (often called the 'outcome' or 'response' variable, or a 'label' in machine learning parlance) and one o ...
designed for estimating the magnitude of genetic and environmental effects in
twin studies
Twin studies are studies conducted on identical or fraternal twins. They aim to reveal the importance of environmental and genetic influences for traits, phenotypes, and disorders. Twin research is considered a key tool in behavioral genetics ...
. It is named after
John C. DeFries and
David Fulker
David William Fulker (8 March 1937 – 9 July 1998) was a British behavioural geneticist at the University of Colorado's Institute for Behavioral Genetics. Among positions of esteem, he was elected president of the Behavior Genetics Associatio ...
, who first proposed it in 1985. It was originally developed to assess
heritability of
reading disability
A reading disability is a condition in which a person displays difficulty reading. Examples of reading disabilities include: developmental dyslexia, alexia (acquired dyslexia), and hyperlexia (word-reading ability well above normal for age and ...
in twin studies, but it has since been used to assess the heritability of other cognitive traits, and has also been applied to non-twin methodologies.
[
]
Approach
DeFries–Fulker regression analysis is based on the differences in the magnitude of regression to the mean
In statistics, regression toward the mean (also called reversion to the mean, and reversion to mediocrity) is the fact that if one sample of a random variable is extreme, the next sampling of the same random variable is likely to be closer to i ...
in a genetic trait between monozygotic (MZ) and dizygotic
Twins are two offspring produced by the same pregnancy.MedicineNet > Definition of TwinLast Editorial Review: 19 June 2000 Twins can be either ''monozygotic'' ('identical'), meaning that they develop from one zygote, which splits and forms two em ...
(DZ) twins. In DF regression, the first step is to select probands in a twin study selected with extreme scores on the trait being studied, and to regression to the mean among their co-twins depending on whether the probands are part of a MZ or DZ twin pair. DF regression is thus based on the assumption that, to the extent that genetic factors play a role in causing the extreme variation in the studied trait, the magnitude of regression to the mean should be greater in DZ co-twins of probands than in their MZ counterparts.[
]
Modifications
Since the DF regression approach was first proposed in 1985, other researchers have proposed modified versions of the DF model that take additional factors into account, including observed covariates and opposite-sex DZ twins.
Regression analysis
The probands are chosen with scores that fall below a "cutoff" for what is considered "extreme", and regression is then used to predict the co-twin scores based on those of the probands and a term reflecting whether the twin pair is MZ (1.0) or DZ (0.5).[ By comparing MZ and DZ co-twins in this manner, an estimate of "group heritability" is generated.]
References
Regression analysis
Behavioural genetics
Quantitative genetics
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