Statistics show that first-born children are overrepresented among incumbents in various political offices. Singletons are also statistically overrepresented while middle and later-born children are underrepresented. This study intends to develop a hypothesis as to the cause of this phenomenon. A child's birth order status affects development in two aspects: parental interaction and sibling interaction or lack thereof. Singletons receive all of their parents' investment, in means of attention, finance, energy, and enthusiasm. First-born children receive the same investment, until a second child causes a reduction of parental resources. The existence of siblings provides first-born children with a different social experience that only children do not have the opportunity to receive.
The study utilizes data for nearly 1200 incumbents in local and national political offices in the Netherlands. Birth order data gained resulted from a mailed questionnaire consisting of brief questions about their age, sex, political office and 4 birth order questions: "Do you have an older brother?", "Do you have an older sister?", "Do you have a younger brother?", and "Do you have a younger sister?" A random sample of one thousand three hundred and fifty local councilors were drawn from a list of twenty-five thousand, with nine hundred and eighty-three questionnaires were returned representing both councilors, part-time and fulltime alderman. All one hundred and fifty national Members of Parliament received the questionnaire and one hundred and nine replied. Birth order data of sixty-six national ministers was obtained by the questionnaire and date for three more obtained via published sources, however the total population is unknown.
Within the family unity, a particular birth order position determines the relationship with parents and to a particular pattern of behavior with siblings. The authors had two different hypotheses as to why certain birth-order statuses statistically held political office more than others: sibling interaction and parental investment. The findings of an overrepresentation of both first-born and only children suggest that parental interaction and investment affects the competence and ambition to obtain a political office. Results also suggest that birth-order distribution amongst sexes demonstrates no significant difference between male and female leaders. A larger percentage of female leaders held the status of first-born or only than their male counterparts, however this is becoming less of a statistic through younger generations. Sibling interaction likely plays a role in providing a training ground especially to first-born incumbents, but does not outweigh the impact of attention, anxiety, and investment from parents.
The comparison to sibling rivalry to "training ground" is the most interesting point of this article for me. First-born children have to share parental resources after the birth of the second child, but gain experience wielding power over the younger siblings. Parents typically depend on the older children to fulfill certain roles such as helping their siblings with homework and baby-sitting while the parents are occupied. The point of this comparison, is to show that singletons do not experience this type of interaction with family members, however I think it is safe to assume that a child that never has to compete for attention for home may do so at school and other social environments. Only children are not isolated from interaction with age-mates, just typically limited in the very early years and in the home environment.
This study expanded on another study whose limitation was that it did not consider only children in its data, only first, middle, and last. It allowed the authors to be able to distinguish between the sibling interaction and parental investment theories unlike previous studies. This study mentions that trends are changing due to an overall change in society. This trend is moving towards a "slow erosion of the overrepresentation of singletons and first-born children." Such societal progress as women's liberation, feminism, increased quality of life, better parental education, child rearing planning, and the trend to have less children all affect the way current and future generations assume leadership roles. The results of this study may not apply in ten - twenty years when a new generation of incumbents take office.
This study speculates that firstborn and only children receive more parental investment thus increasing the capability and likeliness for these birth orders positions to hold political office. A survey of experiences by Roberts and Blanton (2001) observed that many only children felt like "small adults" and were comfortable connecting with other adults at an early age. Roberts and Blanton (2001) also saw this trend carry over into adulthood, with friends and relationship partners typically being a few years their senior. This ability to effectively relate and communicate with elders is a necessary talent for politicians. The reverse is also true; however, it is easier vote for and respect a mature, well spoken adult than a seemingly immature young adult. Firstborns and onlies learn confidence and are often pushed by the parents to succeed. A politician needs these qualities to win votes and be successful in office.