Glossary

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z


A

A

Age Class / Age Group

In HKCaR, two types of age groups are generally used for cancer statistics:

  • Board, the population is classified into 4 age groups: 0-19, 20-44, 45-64 and 65+ years;
  • Quinquennial (5 year's interval), the population is classified into 18 age groups: 0-4, 5-9, 10-14, ... , 80-84, and 85+ years.
And, three types of age groups are applied for Children and Adolescents due to different cut-off ages:
  • Type 1 (Age range: 0-14 years), the population is classified into 4 age groups: 0, 1-4, 5-9 and 10-14 years;
  • Type 2 (Age range: 0-18 years), the population is classified into 5 age groups: 0, 1-4, 5-9, 10-14 and 15-18 years;
  • Type 3 (Age range: 0-19 years), the population is classified into 5 age groups: 0, 1-4, 5-9, 10-14 and 15-19 years.

A

Age-specific Rate
The age specific rate (ai, per 100,000 population) is a ratio of the event for the specific age group i. It is calculated by dividing the number of cases in the age class i (ri) by the corresponding population-at-risk (ni) and multiplying the result by 100,000. Thus,
ai =
ri / ni
× 100,000

A

Age-standardized Rate

Standardization is necessary when comparing several populations with different age structures or for the same population over time in which the age profiles change accordingly. Comparisons with rates from other sources are valid only if they use the same standard population for calculations. Rates in HKCaR's website are standardized to the age distribution of "New WHO World Standard Population (WHO 2000)", unless otherwise specified.

The age-standardized rate (ASR, per 100,000 population) in accordance with direct method is calculated by summing up the products of the age-specific rates (ai, where i denotes the ith age class) and the number of persons (or weight) (wi) in the same age subgroup i of the chosen reference Standard Population, then dividing the sum of Standard Population weights, i.e.

ASR =

Σaiwi

/

Σwi

× 100,000

Cases of cancer of unknown age may be included in a series. An adjustment is made by multiplying the derived ASR by

   R

/

Σri

where

R denotes the total number of cases;

A denotes the number of age groups;

Σri = r1 + r2 + r3 + ··· + rA, where ri denotes the number of cases occurred in the ith age class;

A

Average Annual Percent Change
Average Annual Percent Change (AAPC)1 is a summary measure of the trend over a specified interval. It is computed as a weighted average of the annual percent changes over a period of years from the joinpoint regression model2. In HKCaR, the recent 25 years of available data are generally used to estimate the AAPC of age standardized rate over the past ten years.

For details of calculation, please refer to the website of National Cancer Institute.

References:
  1. Clegg LX, Hankey BF, Tiwari R, Feuer EJ, Edwards BK. Estimating average annual percent change in trend analysis. Statistics in Medicine 2009; 28(29): 3670-82.
  2. Kim HJ, Fay MP, Feuer EJ, Midthune DN. "Permutation tests for joinpoint regression with applications to cancer rates" Statistics in Medicine 2000; 19:335-351: (correction: 2001;20:655).


C

C

Carcinoma in-situ
Carcinoma in-situ (Ca in-situ) is non-invasive and the earliest form of cancer. Abnormal cells are present but have not spread to surrounding tissues or other parts of the body.

C

Crude Rate
The crude rate (C, per 100,000 population) is the ratio of the number of people in which the event happens in a specific time period to the population-at-risk. It is calculated by dividing the total number of cases (R) by the total number of population-at-risk (N) and multiplying the result by 100,000 for common interpretation, i.e.
C =
R / N
× 100,000

C

Cumulative Rate
The cumulative rate (CR%, unit: %) is the sum over each year of the age-specific incidence rates. It can be interpreted as an approximation of cumulative risk. The cumulative rate can be expressed as

CR% = 100 × Σaiti

where ai is the age-specific incidence rate in the ith age class, ti is the width of the ith age class, and the sum is until age class A. Assuming five-year age classes have been used in the calculation, the cumulative rate for age 0-74 can be expressed as

CR%74 = 100 × Σ5ai

This calculation is theoretical and assumes that no death occurs in the period, and that age-specific incidence rates will be stable for an individual.

For illustration of the calculation, please refer to "Chapter 11 Statistical methods for registries, P.Boyle and D.M. Parkin, International Agency for Research on Cancer".

C

Cumulative Risk
The cumulative risk (or lifetime risk, unit: %) refers to the risk an individual would have of developing or dying from a particular cancer over his life span in the absence of any other cause of death. It can be expressed as
Cum. Risk = 100 × [1 - exp (- CR% / 100)]
For illustration of the calculation, please refer to "Chapter 11 Statistical methods for registries, P.Boyle and D.M. Parkin, International Agency for Research on Cancer".

C

Cytology
Cytology refers to diagnosis is determined by examining the cells under a microscope.


D

D

DCO%
DCO%, one of the common quality indicators for assessing data completeness, is the percentage of cases which the information came from death certificate only. A high DCO% implies high proportion of incomplete case ascertainment due to failure to capture cases while patients are alive. (See also MV%)


H

H

Histology
Histology refers to diagnosis is determined by examining the histological characteristics of tissues or cells under a microscope, whilst the histology of a cancer refers to the microscopic characteristics of a tumor.


I

I

International Classification of Diseases (ICD)
International Classification of Diseases (ICD) compiled by World Health Organization (WHO) is used to classify diseases and code diagnoses. In Hong Kong, ICD-9 (the 9th Revision of ICD) and ICD-10 (the 10th Revision of ICD) are commonly used to code malignant cancer cases. For the sake of consistency, those primarily based on ICD-9 are converted to grouped ICD-10 codes.

I

International Classification of Diseases for Oncology (ICD-O)
International Classification of Diseases for Oncology (ICD-O) compiled by World Health Organization (WHO) is a dual-axial classification, with coding systems for both topography and morphology. It is principally used in cancer registries and pathology reports.

I

Incidence
Cancer incidence is the number of new cancer cases arising in a specified population over a given time period. It can be either expressed as an absolute number of cases per year or as a rate per 100,000 persons per year.


M

M

Male : Female ratio
The sex ratio is the number of males for each female in a population.
  • A ratio above 1 means there are more males than females; for instance, a ratio of 1.23:1 means there are 1.23 males for every 1 female.
  • A ratio of 1 means the numbers of males and females are equal.
  • A ratio below 1 means there are more females than males; for instance, a ratio of 0.88:1 means there is 0.88 male for every 1 female.

M

Median age
Median age is the age at the mid-point when the individuals are ranked by their age.

M

Morphology
The morphology of a cancer refers to the histology and biological behavior of a tumor.

M

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

M

Mortality-to-Incidence ratio
The Mortality-to-Incidence ratio (MIR) serves as a population-based indicator to evaluate disparities in cancer screening, incidence, treatment, and survival. It is defined as the age-standardized mortality rate divided by the age-standardized incidence rate. i.e.
MIR =
ASRmortality / ASRincidence

M

MV%
Morphological verification refers to cases for which the diagnosis is based on histology or cytology. MV%, one of the common quality indicators for assessing data completeness, is the percentage of cases with a morphologically verified diagnosis. Higher the MV%, higher the accuracy of diagnosis. (See also DCO%)


P

P

Population-at-risk (also known as person-years at risk)
Population-at-risk is the population that is exposed to the occurrence of an event (e.g. developing or dying from cancer) over a given time period. Generally, the population estimates are used to approximate the population at risk. The Hong Kong Cancer Registry adopts the mid-year population estimates provided by the government's Census and Statistics Department for this quantity.

P

Prevalence
The prevalence of cancer is an estimate of the number (or proportion of) the population alive on a specific date who had been diagnosed with cancer.
(Note: The HKCaR has yet to provide cancer prevalence in Hong Kong.)


S

S

Stage
Cancer staging provides information about the extent of disease spread, usually classified as stage I to IV or unknown. The classification of staging is primarily based on the American Joint Committee on Cancer (AJCC) and Union for International Cancer Control (UICC) TNM staging system for most cancer sites. The HKCaR only records stage at diagnosis for invasive cancers.

In general, an overall stage of 0, I, II, III and IV can be assigned for most cancers according to the combination of T (describes the size of tumor), N (describes whether the tumor has invaded to the nearby lymph nodes) and M (describes whether the tumor has metastasized to other parts of the body):

  • Stage 0 describes carcinoma in-situ in which abnormal cells are present;
  • Stage I, also known as early-stage cancer, indicates a tumor is present but it has not grown into nearby tissues and has not spread to the lymph nodes or other parts of the body;
  • Stage II and Stage III indicate larger tumors have grown deeply into nearby tissues, which may have also spread to lymph nodes but no other parts of the body;
  • Stage IV, also known as advanced-stage cancer, indicates the tumor has spread to distant parts of the body.
For detailed information on cancer staging, please refer to the website of AJCC or UICC.

S

Standard Population
Standard population is the age distribution used as weights to create age-adjusted statistics. The most widely used has been the World Standard population modified by Doll et al., (1966) from that proposed by Segi (1960).

The sum of standard population weights (wi, where i denotes the ith age class) is 1, i.e.

Sum of weights = Σwi = 1 , where A = 18.

The table below shows various standard populations which have been used for age-adjusting in different countries.

Distribution of World Standard Populations (in percent)

Age Class index (i) Age Group Segi 1960 World Standard
(Segi 1960)
New WHO World Standard
(World 2000)
2000 US Standard
(US 2000)
European Standard
(European)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
0-4
5-9
10-14
15-19
20-24
25-29
30-34
35-39
40-44
45-49
50-54
55-59
60-64
65-69
70-74
75-79
80-84
85+
12.00
10.00
9.00
9.00
8.00
8.00
6.00
6.00
6.00
6.00
5.00
4.00
4.00
3.00
2.00
1.00
0.50
0.50
8.86
8.69
8.60
8.47
8.22
7.93
7.61
7.15
6.59
6.04
5.37
4.55
3.72
2.96
2.21
1.52
0.91
0.63
6.91
7.25
7.30
7.22
6.65
6.45
7.10
8.08
8.19
7.21
6.27
4.85
3.88
3.43
3.18
2.70
1.78
1.55
8.00
7.00
7.00
7.00
7.00
7.00
7.00
7.00
7.00
7.00
7.00
6.00
5.00
4.00
3.00
2.00
1.00
1.00
All Ages 100 100 100 100

S

Survival rate
Cancer survival rate is the proportion of patients alive at some point subsequent to the diagnosis of their cancer. It is represented as the probability of a group of patients "surviving" a specified amount of time (E.g. 3 years, 5 years or 10 years).


T

T

Topography
Topography is the site in the body where the tumor is located.