 Incidence


Incidence is the number of new cases arising in a given period in a specified
population. This information is collected routinely by cancer registries. It
can be expressed as an absolute number of cases per year or as a rate per
100,000 persons per year (see agespecific rate and ASR below).
The rate provides an approximation of the average risk of developing a
cancer.

 Mortality


Mortality is the number of deaths occurring in a given period in a specified
population. It can be expressed as an absolute number of deaths per year or as
a rate per 100,000 persons per year.

 Relative survival


Relative survival is defined as the ratio of the observed survival in the group of patients to the survival expected in a group of people in the general population, who are similar to the patients with respect to sex, age and calendar time at the time of diagnosis. It can be interpreted as the probability of patient survival in the absence of other causes of death. NORDCAN generally use cohort methods, following op patients for death for 1 and 5 years after diagnosis, and also 10 years for breast and prostate cancers. For the later periods not all patients can be followed up for 5 or 10 years, and calculations supplement with survival experience for patients diagnosed earlier years, called hybrid methods. Agestandardisation uses the International Cancer Survival Standards (ICSS).
International Cancer Survival Standards (ICSS).
Three standard weight functions (W) for agestandardisation of relative survival as
used in Nordic cancer survival study 19642003. 
Standard 
ICSS 3 
ICSS 2 
ICSS 1 
Characteristics 
Young adults 
Little age dependency 
Elderly 
% of cancers 
2.5 
10.2 
87.3 
Cancer sites 
Testis, Hodgkin lymphoma 
Acute lymphatic leukaemia 
Bone 
Melanoma, cervix, brain, thyroid, soft tissue 
Other sites and summary groups 
Age groups and weights (W) in %
 Ages 
W 
Ages 
W 
Ages 
W 
Ages 
W 
Ages 
W 
029 
31 
029 
31 
029 
7 

3039 
21 
 
3039 
13 

4049 
13 
3049 
34 
4049 
16 
049 
36 
049 
12 

5059 
19 
5059 
17 
5069 
20 
5069 
20 
5069 
41 
6069 
22 
6069 
27 

7079 
10 

7079 
16 
7079 
29 
7089 
15 
8089 
5 
7089 
23 
8089 
7 
8089 
15 
90+ 
0 
90+ 
0 
90+ 
0 
90+ 
0 
90+ 
0 

 Prevalence


The prevalence of a particular cancer can be defined as the number of persons
in a defined population who have been diagnosed with that type of cancer, and
who are still alive at the end of a given year, the survivors. For persons with
more than one cancer the person is included as a prevalent cancer in each
cancer site from the time of diagnosis of that cancer and in the 'All cancer
but nonmelanoma skin' group from the first diagnosis.
Total prevalence represents the number of previously diagnosed
persons alive at the end of a year regardless of how long ago the diagnosis was, or
if the patient is still under treatment or is considered cured. Partial
prevalence, which limits the number of patients to those diagnosed
during a fixed time in the past, is a particularly useful measure of cancer
burden. Prevalence of cancers based on cases diagnosed within one,
three, five, ten and all years are presented in NORDCAN, as they are
likely to be of relevance to the different stages of cancer therapy, namely,
initial treatment (one year), clinical followup (three years) and cure (five
years). Patients who are still alive five years after diagnosis are usually
considered cured since the death rates of such patients are similar to those in
the general population. There are exceptions, particularly breast cancer. Prevalence is available both as numbers and as proportions per 100.000 persons. Agestandardised prevalence proportions are available for comparing countries, offering a choice of World(W), European(E) and Nordic(N) agestandards as for incidence and mortality.

 Population at risk


The part of a population which is susceptible to develop a specific cancer. It
is defined on the basis of demographic data, such as place of residence, sex,
age group, etc. Years of risk duration are counted in personyears.

 Agespecific rate


The agespecific rate is calculated simply by dividing the number of new
cancers or cancer deaths observed in a given age category during a given time
period by the corresponding number of person years in the population at risk in
the same age category and time period. For cancer, the result is usually
expressed as an annual rate per 100,000 personyears. In NORDCAN, fiveyear age
categories are used (highest group 85+).

 Crude rate


Data on incidence or mortality are often presented as rates. For a specific
tumour and population, a crude rate is calculated simply by dividing the number
of new cancers or cancer deaths observed during a given time period by the
corresponding number of person years in the population at risk. For cancer, the
result is usually expressed as an annual rate per 100,000 persons at risk.

 ASR (agestandardised rate)


An agestandardised rate (ASR) is a summary measure of the rate that a
population would have if it had a standard age structure. Standardisation is
necessary when comparing several populations that differ with respect to age
because age has such a powerful influence on the risk of cancer. The ASR is a
weighted mean of the agespecific rates; the weights are taken from population
distribution of the standard population. The most frequently used
standard population is the World Standard Population. The calculated
incidence or mortality rate is then called agestandardised incidence or
mortality rate (world). It is also expressed per 100000. The European standard
is often used and NORDCAN gives the possibility of also choosing a Nordic
standard where the agedistribution is from the NORDCAN population in 2000.


Age distributions of the standard populations used for age
standardisation in NORDCAN (per 100,000) 
Age group 
World
ASR (W) 
European
ASR (E) 
Nordic
ASR (N) 
04 
12000 
8000 
5900 
59 
10000 
7000 
6600 
1014 
9000 
7000 
6200 
1519 
9000 
7000 
5800 
2024 
8000 
7000 
6100 
2529 
8000 
7000 
6800 
3034 
6000 
7000 
7300 
3539 
6000 
7000 
7300 
4044 
6000 
7000 
7000 
4549 
6000 
7000 
6900 
5054 
5000 
7000 
7400 
5559 
4000 
6000 
6100 
6064 
4000 
5000 
4800 
6569 
3000 
4000 
4100 
7074 
2000 
3000 
3900 
7579 
1000 
2000 
3500 
8084 
500 
1000 
2400 
85+ 
500 
1000 
1900 
Total 
100000 
100000 
100000 

 Cumulative risk


Cumulative incidence/mortality is the probability or risk of individuals getting/dying from the disease within a specified age interval within a time period. For cancer and from age 0, it is expressed as the number of new born children (out of 100) who would be expected to develop/die from a particular cancer before the age of 75 or (80 or 85) if they had the rates of cancer observed in the period in the absence of competing causes. Like the age standardised rate, it permits comparisons between populations of different age structures.

 Standard error

The standard error of a rate is a measure of the sampling variability of the
rate.

 Confidence interval

A range of values that has a specified probability of containing the unknown
true rate or trend. The 95% (pvalue = .05) and 99% (pvalue = .01)
confidence intervals are the most commonly used.

 Estimated annual percentage change (EAPC)

The estimated annual percentage change is used to describe the magnitude of
change in the trend on fitting a simple regression model to the log of the ASR.
It is the average annual rate of change in the ASR over the time
period selected.
