“…24,25 The majority of studies were conducted in the UK, Scandinavia and Canada; however, a smaller number of studies took place in other European countries, Asia and Australia. 26,27,28,29,30,31,32,33 Methodologically, most studies lacked appropriate comparison samples or did not collect data prospectively at intervals (data collection periods ranged from 1 month to over 10 years, with a median of 36 months), and instead were cross-sectional and observational, describing a single group of participants (Table 2). For studies that included a comparison group, there was variability in the amount of detail provided, with some specifying sampling strategies or matching criteria 34 and others providing little information.…”