The National Cancer Registry Ireland

Frequently Asked Questions regarding Online Data

Data

• Where do you get your incidence data?
• Where do you get your population data?

Usage and Results

• Why are there such limits on the data?
• What is the National Cancer Registry's policy on confidentiality?
• What do the different behaviours mean?
• Why is there such an increase in rates for prostate cancer?
• Why is the sum of the rates over all the counties in a health-board slightly different to the rates of that healthboard as supplied by the website?
• Why is the sum of incidence / mortality rates, such as C00, C01, ..., C15 different to the totals (e.g. C00-C14) supplied by the website?
• Why is the number of cases in Tipperary (Total) greater than the sum of the cases in Tipperary North and Tipperary South for some years?

Rates

• What is an Age-Specific Rate?
• What is an Age-Standarised Rate?
• What is the Percentage of Total?
• What is the Crude Rate?
• What is the European Age-Standardised Rate (EASR)?
• What is the World Age-Standardised Rate (WASR)?
• What is the Cumulative Risk to age 74?
• Which rate should I use?

Technical Issues

• What is the difference between Comma Separated Format (CSV) and Excel Spreadsheet Format (CSV)
• What do I need to do to see the graphs?
• When I try to copy and paste the graphs into Microsoft Word, I just see a lot of strange text. How do I paste the graph?
• Why won't the graphs print for me?

Answers

Data

Where do you get your incidence data?

The National Cancer Registry collects cancer data itself:

actively:

by employing workers to go to hospitals and other health care centres regularly to look through records for new cases of cancer

passively:

by waiting to be notified of new cancer cases by doctors, nurses, laboratories and so on, and by processing death certificates.

In recent times, the Registry has also begun to put the necessary technologies in place to receive data electronically. It is hoped that this will speed up registration in the future.

Where do you get your population data?

Population data is supplied by the Information Management Unit at the Department of Health of Children . It part of a package of statistical information called the Public Health Information System or PHIS for short.

The population data given gives populations for each age-group in every county and healthboard in Ireland, and in Ireland as a whole. It also gives the overall populations for each county, healthboard and Ireland.

However, for any given area, the sum of the age-specific populations will not generally add up to the overall population for that area. Further, the sum of the populations for the counties does not match the overall population for Ireland.

The registry uses the data as follows:

• The age-specific populations are used for age-specific rates, which are themselves the basis of most age-standardised rates.
• Where the overall population of a location is needed (e.g. the crude rate) we use the sum of the age-specific populations instead of the given value for consistency.
• The population figures for each healthboard are based on the sum of the county populations
• The population figures for Ireland are the figures supplied in PHIS.

Usage and Results

Why are there such limits on the data?

The Registry tries to make as much data as possible to the public. However we are bound by our Confidentiality Policy and cannot release to the public any information which might identify a particular individual. Thus we use different configurations to allow us to provide as much data as possible without compromising the privacy of a citizen.

If you are looking for a particular piece of information you can make a request for data and, if it does not contravene our Confidentiality Policy we will provide you with the results free of charge.

What is the National Cancer Registry's policy on confidentiality?

The registry's confidentiality policy can be read here.

What do the different behaviours mean?

There are four types of behaviour:

Benign

A benign tumour is usally a slow-growing tumour that may displace but does not invade or infiltrate surrounding tissue; a tumour considered not to have malignant or invasive potential.

In-Situ

An in-situ tumour is one with malignant potential which has remained confined to the tissue in which it originated.

Invasive (also known as Malignant)

An invasive tumour is one that is not (or is no longer) confined to the tissue in which it originated. Most tumours are invasive.

Uncertain

An uncertain tumour is one which, at time of diagnosis, cannot be classified as either benign or malignant.

Why is there such an increase in rates for prostate cancer?

In recent times, a new test for prostate cancer, the Prostate-Specific Antigen (PSA) test has become available. This has helped doctors detect prostate cancers much earlier.

However there are some issues with the test. It may report false positive and false negative results. Further, it does not distinguish between prostate cancers which are life-threatening and those which are not. As a result, its use is somewhat controversial, particularly given the significant side effects which result from procedures needed to diagnose and treat prostate cancers.

The U.S. National Cancer Institute has a web-page which answers several common questions regarding PSA tests .

Why is the sum of the rates over all the counties in a health-board slightly different to the rates of that healthboard as supplied by the website?

The rates are pre-calculated to 14 decimal places at the registry, rounded down to two decimal places and then uploaded to the website.

When you add the rates for all the counties you are dealing with figures which have been rounded to two decimal places. Because of this, a rounding error creeps in, which is not present in the rates supplied by the website which were calculated to 14 decimal places and then rounded down.

Why is the sum of incidence / mortality rates, such as C00, C01, ..., C15 different to the totals (e.g. C00-C14) supplied by the website?

The rates are pre-calculated to 14 decimal places at the registry, rounded down to two decimal places and then uploaded to the website.

When you add the rates for all the tumours yourself, or using the websites "All Cancers Combined" facility, you are dealing with figures which have been rounded to two decimal places. Because of this, a rounding error creeps in, which is not present in the total rates supplied by the website which were originally calculated to 14 decimal places before being rounded down.

Why is the number of cases in Tipperary (Total) greater than the sum of the cases in Tipperary North and Tipperary South for some years?

Most of our data for Tipperary hasn't been geocoded to each of the ridings. Our policy is thus to assign to the North Riding those cases that are registered in the Mid-Western Health Board, and to the South riding those that are registered in the South-Eastern Health Board

Occasionally there are cases where the health board is not given. Such cases cannot be matched to either of the ridings. As a result the rates for "Tipperary (Total)" are generated from the cases assigned to the North Riding, the cases assigned to the South Riding, and those cases which could not be assigned to either riding. It is these unassigned cases which account for the difference.

Rates

What is an Age-Specific Rate

The age specific rate is the number of cases per person in a particular age class, usually for five year age classes up to 85, expressed per 100,000 persons per year.

What is an Age-Standarised Rate

An age-standarised rate is a weighted sum of the age-specific rates which indicates the overall rate for a particular cancer. The two most commonly used age-specific rates are the European Age-Standardised Rate and the World Age-Standardised Rate.

What is the Percentage of Total

The percentage of total figure indicates what proportion of the total cancers incidence / mortality in a given area the current cancer accounts for.

What is the Crude Rate

The crude rate is the number of cases or deaths divided by the population at risk, expressed per 100,000 persons per year.

What is the European Age-Standardised Rate (EASR)

This is the rate that would have been found if the population of Ireland had the same age-composition (proportion of total population in each five year age class) as a hypothetical European population.

The rates are calculated by applying the age-specific rates for the location being studied to a theoretical European standard population, usually expressed per 100,000 persons per year.

What is the World Age-Standardised Rate (WASR)

This is the rate that would have been found if the population of Ireland had the same age-composition (proportion of total population in each five year age class) as a hypothetical world-wide population.

The rates are calculated by applying the age-specific rates for the location being studied to a theoretical world-wide standard population, usually expressed per 100,000 persons per year.

What is the Cumulative Risk to age 74

This is the risk to an "average" individal, given current cancer rates, of developing a cancer before his or her 75th birthday (assuming survival to that date). It is usually expressed as a percentage.

Note that cumulative risk takes no account of differences in risk factors between individuals or of possible future changes in incidence, but is based on the average Irish male or female and the current incidence rates for the population.

Note also that a substantial number of cancers occur in individuals ages 75 years or more. As the normal life expectancy in Ireland is close to 75 years, the cumulative risk to age 74 is a good approximation of the "lifetime risk" of developing a cancer.

Which rate should I use?

The rate you should use depends on the purpose to which you propose to put the data. The European Age-Standardised Rate is a good metric by which to compare rates across Europe, and likewise the World Age-Standardised Rates is useful for comparing rates with countries outside Europe, such as the U.S.

Technical Issues

What is the difference between Comma Separated Format (CSV) and Excel Spreadsheet Format (CSV)?

There is no difference between these formats. In user-testing, it was found that many users did not realise that data in the Comma Separated Format (CSV) would open in their default spreadsheet application, and instead chose the more cumbersome HTML format. We added this second description of the CSV format to aid these users.

What do I need to do to see the graphs?

You need a browser which support the SVG format. See the section on SVG Browser support on this page

When I try to copy and paste the graphs into Microsoft Word, I just see a lot of strange text. How do I paste the graph?

To copy one of the graphs right-click on it and select Copy from the popup menu. By and large you can paste the image into applications using the normal methods. However with Microsoft Word you have to select the Paste Special... item from the Edit menu.

In the dialog that appears, select the Bitmap format and click OK. The image will be pasted into Word.

Why won't the graphs print for me?

There appears to be a bug in the Adobe SVG Viewer which prevents it from printing SVG images over several pages.

The options are limited - you can try using a different browser, select only a handful of graphs at a time, or else copy the graph image, paste it into an image manipulation program, and print it through that.