Passage: Maffei 1 is located only 0.55° from the galactic plane in the middle of the zone of avoidance and suffers from about 4.7 magnitudes of extinction (a factor of about 1/70) in visible light. In addition to extinction, observation of Maffei 1 is further hindered by the fact that it is covered by myriads of faint Milky Way stars, which can easily be confused with its own. As a result, determining its distance has been particularly difficult.In 1971, soon after its discovery, Hyron Spinrad estimated the distance to Maffei 1 at about 1 Mpc, which would place it within the Local Group of galaxies. In 1983 this estimate was revised up to 2.1+1.3−0.8 Mpc by Ronald Buta and Marshall McCall using the general relation between the luminosity and velocity dispersion for elliptical galaxies. That distance puts Maffei 1 well outside the Local Group, but close enough to have influenced it in the past.In 1993 Gerard Luppino and John Tonry used surface brightness fluctuations to derive a new distance estimate to Maffei 1 of 4.15 ± 0.5 Mpc. Later in 2001, Tim Davidge and Sidney van den Bergh used adaptive optics to observe the brightest asymptotic giant branch stars in Maffei 1 and concluded that it is located at the distance 4.4+0.6−0.5 Mpc from the Sun. The latest determination of the distance to Maffei 1, which is based on the re-calibrated luminosity/velocity dispersion relation for the elliptical galaxies and the updated extinction, is 2.85 ± 0.36 Mpc.

Question: What year was the distance estimated?
1971