methods
The research study included longitudinal information, as the study sample were sets of adult twins separated early and raised apart, and then brought back together in adulthood. It included the averages of their years apart and time together before separation in months. They used multiple methods of data collection, having several specialists assess their personalities, their IQs, physiological and psychological profiles, et cetera separately by observation and interview. The subjects also independently completed questionaires, allowing the researchers multiple sources of information to pull from, which is why I believe they were chosen. The combination of these many options and the large sample pool they researched allowed them a broader view of the development with less room for error.
findings
The studies revealed that monozygotic twins raised apart bore similar results to the twins raised together, showing that in a normal situation without abusive or negative parenting, identical twins will develop in related ways regardless of any contact with each other. This conclusion suggests that many of their traits are genetic, something they inherited from the single egg becoming two zygotes. Any variations are the result of their own individual differences and/or situations, but are not extensive enough to set them readily apart. In this study, nature is more dominant over nurture, as they are applied to monozygotic twins that share virtually the same DNA.