Two types of aerosol, A and B were compared in asthmatic patients. 85 patients were included in a cross-over trial. Each patient used each aerosol for a period month, with the order of administration at random. For 19 patients their symptoms were better controlled while on aerosol A and for 36 whilst they were on aerosol B. 26 patients did well on both A and B and 9 failed to complete the trial.

a) Draw a 2 by 2 table [2 marks]

b) Is there any evidence of a difference in the effect between A and B? [7 marks]

c) Write brief summary of what the result show.