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 The South Australian Cancer Registry Major Cancers in South Australia 1977-2005 This section includes graphs for males and females for the ten most common cancers in South Australia and for cervix cancer. Summaries and statistical graphs are provided for each cancer site including male and female trends in cancer incidence and mortality, for the period 1977 to 2005. The graphs are age and sex-standardised to the Australian 2001 population, and are also presented in a three-year moving average format. These graphs give a clear picture of the long term time trends in cancer incidence and mortality in South Australia, and show the impact of screening programs on cancer incidence and mortality for cancers such as breast and cervix cancer. Brief descriptions of some of the statistical techniques used to produce these graphs are given below. The following text outlines how crude, age-specific and age-standardised rates of cancer incidence and mortality have been calculated for the graphs and text in this report. The text comes from the report – Cancer in Australia 1989-1990, P. Jelfs et al. Australian Institute of Health and Welfare, Canberra 1996 (with permission). Example table Trachea, bronchus and lung cancer incidence (ICD 162)-males
*Australian Bureau of Statistics (1993) **Doll & Smith (1982) A cancer incidence rate is defined as the number of new cases of cancer divided by the population at risk in a specified time period. A cancer mortality rate substitutes deaths for new cases in this calculation. Both are conventionally expressed as annual rates per 100,000 population and may be calculated for males, females or persons, or for subsets of the population (e.g. see age-specific rates). The total rate calculated in this way without adjustment for age or other factors is known as the 'crude rate'. The crude rate is calculated by dividing the total number of cases across all age groups by the total population e.g. Crude incidence rate
for lung cancer = column
1 total x 100,000 =
4,896 x 100,000 = 57.4 per 100,000 Age-specific rates RETURN TO TOP Age-specific rates are calculated by dividing the number of cases occurring in each specified age group by the corresponding population in the same age group expressed as a rate per 100,000 population. This rate may be calculated for particular age and sex groupings, e.g: Age-specific lung cancer incidence rates in males aged 75-79 = column 1 for this age
x 100,000 =
722 x 100,000 = 462.6 per 100,000 Age-standardised rates (AS Rate) Rates are adjusted for age to facilitate comparisons between populations which have different age structures, e.g. between youthful and ageing communities. There are two different methods commonly used to adjust for age. In this publication we use direct standardisation in which age-specific rates are multiplied against a constant set of rates (the World Standard Population). This effectively removes the influence of age structure on the summary rate which is described as the age-standardised rate. The method may be used for both incidence and mortality calculations. The method used for this calculation comprises three steps which can be followed by reference to the example table above. Step 1: Calculate the age-specific rate (as shown above) for each age group (column 3). Step 2: Calculate the expected number of cases in each five-year age group by multiplying the age-specific rates (column 3) by the corresponding standard population (column 4) and dividing by 100,000. Step 3: Sum the expected number of cases in each age group to give the age-standardised rate (total column 5). Three Year Moving Average RETURN TO TOP A three year moving average graph is a graph which ‘smooth out’ some of the variability in a graph of annual data. Each point on such a graph is an average of three years worth of data. So for example, the value for 1995 is actually an average of 1994, 1995 and 1996 and the value for 1996 an average of 1995, 1996 and 1997. The smoothing out of the graph makes general trends in cancer incidence and mortality easier to interpret. Material for this document prepared by Adrian Heard of the Health Statistics Unit. SA Cancer Registry Doll R, Smith PG 1982. Comparison between cancer registries: age-standarised rates. In: Waterhose J, Shanmugaratnum K, Muir C eds. Cancer incidence in five continents. Volume IV, Scientific Publications no 42. Lyon: International Agency for Research on Cancer, chapter 11. Australian Bureau of Statistics (ABS) 1994. Projections of the populations of Australia, states and territories 1993 to 2041. cat. no. 3222.0. Canberra: Australian Bureau of Statistics. Links |
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| SA Cancer Registry Department of Health Level 3, 162 Grenfell Street, Adelaide, South Australia 5000 Telephone: (08) 8226-6360 | Facsimile: (08) 8226-6291 E-mail address: Epidemiology@health.sa.gov.au Postal address: PO Box 6 Rundle Mall, Adelaide 5000 |