The dynamics of frailty development and progression in older adults in primary care in England (2006–2017): a retrospective cohort profile oleh Carole Fogg, Simon D. S. Fraser, Paul Roderick, Simon de Lusignan, Andrew Clegg, Sally Brailsford, Abigail Barkham, Harnish P. Patel, Vivienne Windle, Scott Harris, Shihua Zhu, Tracey England, Dave Evenden, Francesca Lambert, Bronagh Walsh, The Frailty Dynamics study team