The Danish researchers enrolled all Danes 30 years or older and born after 1925 and divided them into those with cell phone subscriptions between 1987 and 1990 and those without.
It is also important to note that like all wireless services, the more customers using wireless broadband within a cell or cell sector (cell sites are normally divided into three equal sectors of 120-degree coverage each), the slower the network will appear to those using it.