Modelling the Relationship Between NBA Draft and the Career Longevity of Players Using Generalized Additive Models

Abstract

Draft is an annual event, which distributes players coming from college and overseas among a pool of eligible teams. Selecting a player in the draft is probably one of the most important decisions for NBA front offices. In this study we examined the relationships between NBA draft order of selection and career longevity between 1978 and 1998 using generalized additive models. Retrospective data of 1091 players selected in the NBA draft from 1978 to 1998 was considered. Data was extracted from the NBA official website (http://stats.nba.com/draft/history/) and from a specialized website in basketball (https://www.basketball-reference.com/). The variables considered for analysis were order of player’s selection pick, years played in the league and the year of the NBA Draft. We assumed the possibility of non-linear patterns in the relations between Draft pick order, career longevity and years of draft selection, hence modeling these variables using a bivariate tensor spline. On average, players selected in the first five picks of the NBA had a longer career (~14 career years). Controlling for draft years, a non-linear trend of career longevity was observed with a decrease in the career longevity from the first pick until the 30th pick, leveling of thereafter. When accounting for draft pick, a non-linear trend was observed for career longevity per draft year. Career longevity increased between 1978 and 1985, leveling between 1985 and 1993 and increasing in the following years until 1998. Overall, the longevity of NBA careers has increased for players selected in the first picks of the NBA drafts of the most recent draft years.