 In 2008, data appeared on a study of prostitution across the Nordic region by the Nordic Gender Institute (NIKK), including work done by several authors from the different Nordic countries (Denmark, Finland, Iceland, Norway, Sweden).The number of sex workers working in Sweden before and after 1999 law reform has been described as "difficult to determine" by Skilbrei.In Skilbrei and Holmström's critical review of the data and reports that have been published, they note that knowledge concerning the size of the market before the ban was primarily based on whom the social workers came into contact with.