To reconstruct the population at risk for the population and its respective regions, we took advantage of published census reports from 1911, 1921, 1931, and 1948. Annual sex and age specific population at risk taken at four-year intervals beginning with one year olds was interpolated by using age-specific multipliers applied to the age and sex specific population sizes from the census of the closest year. The total population, we estimated, fell within a margin of less than 0.5% of the total population as cited in the annual Health Reports. Yearly birth rates, retrieved and compiled from the monthly Malta Gazette death records where live birth information was recorded, gave the approximate number of infants under one year of age. This approach assumed that stability in the proportions of individuals at risk for each age band over the decennial period. Using the aforementioned data sources, we compiled the overall as well as the sex and age specific (15 to 44 years) annual tuberculosis mortality rates for Malta from 1911 to 1949.
We recognize potential limitations in historical studies of tuberculosis. Since tuberculosis was often incorrectly identified as the cause of death, it is inherently possible that we overestimated our rates of tuberculosis mortality. At the same time, there was no sure method of confirming cases and causes of death even by World War I when portable x-rays were used, but not readily available, so that many were diagnosed without the confirmation of x-rays. For this latter reason, some have argued that the improvement in diagnosis over time has been partly responsible for the decline in tuberculosis deaths.
Using census returns and their protocol for defining the residential settlement type, we divided Malta's settlements into three distinct settings: (1) urban and suburban setting, (2) rural setting, and (3) Gozo. We used Malta's administrative definition of the respective regions as specified in the Census returns of 1911 and 1921, and the Annual Health Reports.
Because of the varying degrees of dependency on the importation of foodstuff across the Maltese islands, we used food imports as a proxy measure of the cost of living, which can be examined for its effectiveness as an explanatory variable for the rates of respiratory tuberculosis mortality over time and within the three regions. Data on economic parameters used to construct the price and quantity index, the chained linked Fisher index, for 1910 to 1938 (years 1916 and 1920 were excluded from the study), was sourced from the importation of goods information found in the Malta Blue books. J. Falzon generously supplied the values for the Fisher index as presented in Falzon and Lanzon, 2011. We chose it for its superiority as a price and quantity index because it satisfies most of the desirable properties of an index (see the 10 properties as outlined in and as originally presented by Diewert, 1987). The Fisher index is a measure of inflation based on house consumption and unit price values, and is the square root of the Laspeyres index multiplied by the Paasche index. We analyzed the relationship of economics to tuberculosis death rates (overall and regional) using least square regression and Pearson's correlation analysis. Data on tuberculosis deaths, by sex and age, and population at risk are included in the supporting information (See S1 Dataset).