In this regard, as mentioned above, the initial $1-a-day poverty line was based on the common (national) poverty lines of 6 of the poorest countries out of a sample of 33 developing countries studied by Ravallion, Datt and van de Walle (1991) who used 1985 Penn PPP values. However, Chen and Ravallion (2001), after having recomputed this line using 1993 Penn PPP values and taking the median of the lowest 10 national poverty lines of the same country sample, suggested a poverty line of $1.08 per day. They later switched to a new set of PPPs (for 2005) computed by the World Bank and suggested a poverty line of $1.25 per day based on the mean of the poverty lines of the 15 poorest countries of the sample (Chen and Ravallion (2008)).