Author's response: understanding the natural progression in %FEV1 decline in patients with cystic fibrosis: a longitudinal study. Issue 3 (4th December 2012) - Taylor-Robinson, David; Whitehead, Margaret; Diderichsen, Finn; Olesen, Hanne Vebert; Pressler, Tania; Smyth, Rosalind; Diggle, Peter