Freedman et al. (2001) give the relative velocity and the distance of 24 galaxies, according to measurements made using the Hubble Space Telescope – the data are contained in the gamair package accompanyingWood (2006), see Table 6.1. Velocities are assessed by measuring the Doppler red shift in the spectrum of light observed from the galaxies concerned, although some correction for ‘local’ velocity components is required. Distances are measured using the known relationship between the period of Cepheid variable stars and their luminosity. How can these data be used to estimate the age of the universe? Here we shall show how this can be done using simple linear regression.