A statistical time series analysis was applied to the new version 8 merged Solar Backscatter Ultraviolet (SBUV) data set of ozone profiles for the years 1979--2003. Linear trends for the 1979--1997 time period are reported and are compared to trends computed using ozone profiles from the Goddard Space Flight Center (GSFC) zonally averaged coupled model. Observed and modeled annual trends between 50¿N and 50¿S were a maximum in the higher latitudes of the upper stratosphere, with Southern Hemisphere (SH) trends greater than Northern Hemisphere (NH) trends. The observed upper stratospheric maximum annual trend is -7.0 ¿ 2.0%/decade (2σ) at 47.5¿S and -4.7 ¿ 1.3%/decade at 47.5¿N, to be compared with the modeled trends of -5.8 ¿ 0.3%/decade in the SH and -5.2 ¿ 0.3%/decade in the NH. Both observed and modeled trends are most negative in winter and least negative in summer, although the modeled seasonal difference is less than observed. Model trends are shown to be greatest in winter because of a repartitioning of chlorine species and the increasing abundance of chlorine with time. The model results illustrate the trend differences that can occur at 3 hPa depending on whether ozone profiles are in mixing ratio or number density coordinates and on whether they are recorded on pressure or altitude levels.