For investors in GlaxoSmithKline ( LSE: GSK ), though, neither of these qualities have been in evidence during recent years. Its shares have only marginally outperformed the FTSE 100 over the last five years, up by 14% versus 12% for the wider index. Furthermore, GlaxoSmithKline's bottom line has fallen by a third in the last four years as it has struggled to overcome sales declines on a number of key drugs and treatments.