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Frequently asked questions

What is cancer incidence and where is the data from?

Incidence is the number or rate (per head of population) of new cases of cancer diagnosed in a given population in a defined time period (in this case a year). This does not include secondary cancers or recurrences.  

The data has been sourced by Macmillan from the N. Ireland Cancer Registry (NICR). The NICR has calculated incidence based on their database of cancer patients in NI.

N. Ireland Cancer Registry (NICR). Data extract. 2017.

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What are the tumour groups included for incidence and mortality?

There are 22 cancer types (or tumour groups) included for incidence and mortality on this site, including 'All cancers'.

The tumour groups included for incidence and mortality along with their corresponding international classification of disease (ICD10) codes are listed in the general FAQs section, what cancer types are included?

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What are age-standardised rates and why have they been used?

Age has a big impact on cancer as older people are more likely to be diagnosed with cancer.  This means older populations will usually have higher cancer incidence.  Age-standardised rates model the population onto a reference age profile.  This allows analysts and policy makers to see the differences in incidence that are not caused by the differences in age profile.  Age standardised rates are therefore useful to compare locations with different age populations.  When populations are ageing looking at age-standardised trends over time can be useful for learning about the increase or decrease in risks other than ageing.

Age-standardised rates are calculated by taking the age-specific crude rates and applying them to the age distribution of a hypothetical reference population, in this case the 2013 European Standard Population (ESP).                                                                                                                  

Until recently age-standardised rates have been calculated using the 1976 ESP.  This change in population for the calculations may mean that the rates presented here are higher than those in other sources, previous publications or higher than expected. Compared to the 1976 ESP, the 2013 ESP places greater weight on older age groups, which more closely reflects the age distribution in current European populations. For this reason, and because both cancer diagnoses and deaths are more common amongst older age groups, age-standardised rates calculated with the 2013 ESP are likely to be much higher than those calculated with the 1976 ESP; the rates calculated with the 2013 ESP are also more likely to reflect the true rates in the population at the current time.

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What does it mean when we say "higher than", "lower than" or "similar to" the Northern Ireland average for incidence and mortality?

The reference to "higher than", "lower than" or "similar to" indicates whether the age-standardised rate for the locality is statistically significantly different to the England average.

When looking at data sometimes differences may be due to chance and depends on the quality, random and natural variation of the subject of interest. The difference we highlight is defined by comparing the confidence intervals for the local area with the rate for England. Confidence intervals are used to show the range around a data point where we are, in this case, 95% sure that the true value lies, so is a measure of how confident we are that the statistic is true.

"Higher than" indicates the local rate is significantly higher than the Northern Ireland average and this difference is unlikely to be due to chance i.e. we are 95% sure that the figure is different.

"Lower than" indicates that the local rate is significantly lower than the Northern Ireland average and this difference is unlikely to be due to chance.

"Similar to" indicates that local rate is not significantly different – the numbers may not be identical but we cannot be sure that the true difference is not due to chance so we say that the local figure is not significantly different to the Northern Ireland average.

The statistical comparison is based on Standardised Incidence Ratio (SIR).  This is the ratio of the real number of cases observed in a region of Northern Ireland to the number of cases expected if the Northern Ireland overall age-groups specific rates were operative. For more details of these SIR see the statistics provided by the N. Ireland Cancer Registry.

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What is cancer mortality and where is the data from?

Cancer mortality is the number, or rate, of deaths from cancer in a given population in a defined time period (typically a year).

Mortality data relate to all deaths registered with cancer mentioned as a primary or underlying cause of death.

Results may differ slightly than those produced by the Northern Ireland Statistics and Research Agency (NISRA), which produces deaths data based upon the date on which the death is registered with General Register Office for Northern Ireland.

The data has been sourced by Macmillan from the N. Ireland Cancer Registry (NICR).  The NICR sourced the information from General Register Office (GRO) for Northern Ireland.

Source:

N. Ireland Cancer Registry. Data extract. 2017.

GRO Office NI

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