Why are the variables mortality rate and annual cigarette consumption expressed in the log₁₀scale?

Cancer

The following statistics are taken from an article by Burch relating cigarette smoking to lung cancer [13]. The article presents data relating mortality from lung cancer to average cigarette consumption (lb/person) for females in England and Wales over a 40-year period. The data are given in Table 11.19.

 

Table 11.19: Cigarette consumption and lungcancer mortality in England and Wales, 1930ˆ’1969

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Σχ-2.38, Σ1.310, Σ--15.55, i=1 i=1 i=1 Σ-30.708 , ΣΧγ--4.125 i=1 i=1 log., annual cigarette consumption (Ib/ person), x log,, mortality (over 5 years), y Period 1930–1934 -2.35 -0.26 1935–1939 -2.20 -0.03 1940–1944 -2.12 0.30 1945–1949 -1.95 0.37 1950–1954 -1.85 0.40 1955–1959 -1.80 0.50 1960–1964 -1.70 0.55 1965–1969 -1.58 0.55