a milestone for research on gender is the use of meta-analysis, which provides a way to assess patterns in a systematic way, which is especially relevant for a topic such as gender, which can be difficult to quantify. nature and nurture have historically been analyzed when looking at gender in play, as well as reinforcement by peers and parents of typical gender roles and consequently, gender play. toy companies have often promoted the segregation by gender in toys because it enables them to customize the same toy for each gender, which ultimately doubles their revenue. for example, legos added more colors to certain sets of toys in the 1990s, including colors commonly attributed to girls such as lavender.