Methodological differences between the two surveys that restrict the comparison and trend analysis of data
| Survey 1956–1961 | Survey 1991–2008 | |
| Covered area | Urban and periurban area of about 60 km2 at that time Lourenço Marques (today’s Maputo city). | Today’s Maputo city |
| Type of registry | Population-based registry: it included every tumour diagnosed in Miguel Bombarda Hospital (MBH), the two missionary hospitals and the outpatient’s clinics (private and state controlled) in Lourenço Marques. Data of new cancer cases were obtained of biopsies and autopsies performed by the department of pathology of the MBH, but also of home visits. | Laboratory-based registry: it included all tumours diagnosed by anatomopathological test performed in the department of pathology of the Maputo Central Hospital. The department also receives samples of other public and almost all private health units in the city. |
| Population estimates | Due to the steady influx of African rural workers seeking employment in Lourenço Marques, the 1950 census was even more inadequate than African census records usually are.6 In 1957–1958, a sample survey was conducted to ascertain accurate demographic data. At that time, there were no house numbers or guiding maps, random sampling was done using aerial photographs and included the three main residential strata at that time: servants and labourers living on employers’ premises in central area of the town, suburban dwellers living in their own houses on the immediate outskirts of the central area and periurban population. A total of 4291 men and women were included to calculate the population estimates of age and sex distribution. | The first postcivil war Mozambican census was performed in 1980. Although their precision can be questioned, data of the 1980, 1987 and 2007 census were available and intercensual estimates could be calculated. |
| Age estimates and standard populations for age-standardised rates | Due to the high illiteracy rate at the time (97% before the first literacy campaign in 1975), estimating patients’ age was a big challenge. Surveyors were specially trained to establish the age by questioning about critical periods or historical events. Age-standardised rates were calculated using the Standard African Population, a less westernised standard adequate for comparison with other territories of Africa. | The World Standard Population proposed by Segi (1960) was used for age standardisation. This standard is widely adopted, but it reflects to a greater extent population with relatively low fertility and mortality giving more weight to the middle years of life. Applying this standard to ‘younger’ populations can misstate the true level of estimates.38 |
| Extrapolation of data | In both cases, surveys were restricted to today’s Maputo city area. Information of other sites of the country and especially of rural areas is needed for a national-wide extrapolation. | |