RLO: Using Twin and Adoption Studies

• Introduction
• Twin Studies
• Publication Bias
• Example of Twin Study
• Adoption Studies
• Advantages and Disadvantages of Adoption Studies
• Example of an Adoption Study

Publication Bias

Publication bias is an issue to consider when discussing any published research. Publication bias arises from the tendency of researchers and editors to publish studies with positive findings over those with negative findings. Published twin and adoption studies may not be truly representative of all valid studies undertaken. It is important to recognize that publication bias is not a disadvantage of the study design itself but rather the reviewer’s assessment of research and its publication potential.

Advantages and disadvantages of twin studies

Although this is a relatively inexpensive, uncomplicated type of study to perform, identifying suitable sets of twins is not always easy. The zygosity of twins is not normally recorded on birth certificates or in medical records. In many cases genetic tests will be needed to confirm a particular twin pair’s zygosity. Studies are also likely to be based on small numbers of twins. Twin studies may not be applicable to the rest of the population as twins are at greater risk of complications during pregnancy and shortly after birth compared with singletons. These studies are also complicated by the fact that twins are more likely to share the same environment than other siblings and monozygotic twins are known to share their environment to a greater extent than dizygotic twins.