The authors of this study investigate three different hypotheses to reveal the effects of birth order in families, and to prove that there is a significant difference in the firstborn and laterborn children. One of the hypotheses being, that firstborns are more conscientious than laterborns. When speaking of conscientiousness we are referring to them being more responsible, organized, and academically achieving. This is hypothesized to be true because they feel that firstborns tend to support the interest of their parents and show a strong motivation to live up to their parent’s expectations. Where as the laterborn children venture towards a more innovative lifestyle. With firstborns already taking the lead of their parents, the laterborns are left then trying to find themselves and may come off as a rebel or as a less conscious creature. Another hypothesis explored is that laterborns are more open to experience than firstborns. Speaking of their rebellion, being unconventional, and being liberal. The other proposed hypothesis by Beer and Horn is that effects of birth order on personality are caused by prenatal hypomasculinization of younger brothers through progressive immunization of mothers to the H-Y antigen by each succeeding male fetus.
The authors of this study took on the correlation research design in comparing the two different variables, which are firstborn siblings are more conscientious than laterborn and that laterborn are more open to experience than firstborn. The study compares the sibling’s personalities without the manipulations of any variable, which is why we rule out the experimental research design in this study. This study also used self-report data as the source of personality data, using questionnaires that allow them to evaluate their own personality and their sibling’s personality. The study was done twice first given to students of a psychology class at University of Canterbury, later sent out to predominantly older people of New Zealand to rule out the possibility of the findings being subject to young age and rebellious stages of life. In both studies results supported that firstborns are more conscientious than secondborn in. Also supporting that secondborns are also more open to experience than firstborns. The only hypothesis that was not supported was the one proposed by Beer and Horn which suggested that effects of birth order on personality are caused by prenatal hypomasculiniztion of younger brothers through the progressive immunization of mothers to the H-Y antigen by each succeeding male fetus because in both studies the birth order differences in the model tended to