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Measuring Mortality Using Public Data Sources 2019-2023 (October 2019 - June 2023)

Death notices on the website provide close to 'real time' mortality trends in Ireland, analysis shows

CSO statistical publication, , 11am
A CSO Frontier Series Output

This publication is categorised as a CSO Frontier Series Output. Particular care must be taken when interpreting the statistics in this release as it may use new methods which are under development and/or data sources which may be incomplete, for example, new administrative data sources. 

Key Findings

  • A pronounced increase in the number of death notices was observed in late December 2022 and early January 2023.

  • Analysis of death notices provides high quality mortality estimates between 12 and 24 months earlier than official data.

  • A number of approaches to calculating excess deaths estimates are presented in this release which provide a range of estimated excess mortality rather than a single figure for each month.

Statistician's Comment

The Central Statistics Office (CSO) has today (04 October 2023) released an update to the experimental analysis on Measuring Mortality Using Public Data Sources 2019-2023 (October 2019 - June 2023).

The release looks at the period from October 2019 up to the end of June 2023 using death notices placed on the website to monitor trends in mortality in Ireland.

This publication is categorised as a CSO Frontier Series Publication. CSO Frontier Series may use new methods which are under development and / or data sources which may be incomplete, for example new administrative data sources which means care must be taken when interpreting the results.

Commenting on the results, Statistician, Rob Kelly, said: "Since the end of March 2020, the CSO has been using the website to track death notices. Death notices as far back as 01 October 2019 were analysed, to include the last month before the first global cases of COVID-19 were notified. The analysis has now been updated to the end of June 2023. The Death Events Publishing Service (DEPS) of the General Register Office (GRO) has been monitored in tandem, to validate the volumes of death notices published.

Due to the Irish custom of holding funerals within two to three days following a death, these notices are usually placed in a fast and efficient manner, providing a valuable crowd-sourced means of tracking deaths. The notices are placed close to 'real time'. We found that the average length of time between date of death and publication of the notice on the website is about 1.3 days. This most recent analysis shows that death notices provide accurate estimates up to 12 months earlier than official data.

The CSO also conducted further analysis of death notices to provide estimates for excess mortality. In order to demonstrate the complexity around calculating excess mortality, this release presents a number of approaches to calculating excess deaths estimates. This provides a range of estimated excess mortality rather that a single figure for each month.

The analysis conducted for October 2019 to June 2023 shows some important trends. Most notable are the increases in death notices in April 2020 and in January and February 2021. More recently, another significant peak occurred in the last week of December 2022. (See Figure 1 for more information)

The CSO is grateful to for the use of information on their website."


The Central Statistics Office (CSO) has a policy of careful and considered investigation of a data source before employing it to inform official statistics. In Ireland, people have three months to register a death. However, General Register Office (GRO) analysis of deaths occurring between 2016 and 2019, indicates that approximately 82% of all deaths were actually registered within three months. This means it can be many months after the event before official statistics on deaths can be produced. Deaths that are referred to the Coroner’s Court may also take years to be reflected in official statistics due to the length of time to complete the court process. Given the need for more timely data as a result of the COVID-19 pandemic, the CSO began to explore experimental ways of obtaining up-to-date mortality data.

Due to the Irish custom of holding funerals within two to three days following a death, online death notices are usually placed in a fast and efficient manner, providing a valuable crowd-sourced means of tracking deaths. The notices are placed close to 'real time', and since 2021 the average length of time between date of death and publication has remained constant at 1.3 days. When compared with the statutory time limit of three months1 for the registrations of deaths in the State, this is a timelier data source for monitoring trends in mortality.

The CSO published the first analysis of death notices using the website in July 2020. The initial analysis explored the use of death notices posted on to measure trends in mortality, finding a strong correlation between death notices and official CSO mortality statistics. Subsequent analysis in November 2020,  April 2021 and February 2022 continued this work to expand the excess mortality analysis as well as updating the data to include the most recent death notices.

Analysis of death notices was conducted as far back as 01 October 2019, to include the last month before the first global cases of COVID-19 were notified. This updated release covers the period October 2019 to end of June 2023.

Analysis of Death Notices

Figure 1 shows weekly analysis of death notices for the period 01 October 2019 to 02 July 2023 (end of Q2 2023). Plotted alongside this are confirmed COVID-19 deathsas reported to the Health Protection Surveillance Centre (HPSC) by both date of death and by date of notification. Note the COVID-19 deaths by date of death is subject to ongoing revision as notifications come in and/or dates of death are confirmed.  COVID-19 deaths by date of notification tend to have a slight lag in terms of trends but offer a more timely indicator while data on date of deaths is pending.

Figure 1: Weekly Analysis of Mortality Trends Using Public Data Sources, Jan 2020 to June 2023

Figure 1 clearly shows the significant rise in death notices in March to April 2020 and January to February 2021 in line with the impact of the COVID-19 pandemic. From July 2021 to September 2022, there continues to be a general trend of Covid-19 deaths reported that follows the overall rise and fall in the number of weekly death notices. From the start of October 2022, we can see that while there was again a rise in reported Covid-19 deaths, the corresponding increase in death notices was at a much greater rate. This rise in death notices, particularly around the peak in December 2022, closely aligns with HSPC weekly reports which noted very high levels of Influenza and Other Respiratory Viruses circulating in the community at this time. 

"During the 2022/2023 season, excess all-cause mortality was reported over four consecutive weeks (weeks 51 2022 - 2 2023). Excess pneumonia and influenza mortality was also reported over four consecutive weeks (weeks 51 2022 – 2 2023)." Source: HSPC Influenza Surveillance in Ireland – Week 20 2023 Report.

Comparison of Death Notices to Registered Deaths by Occurrence date

This section explores coherence between counts of death notices and officially registered deaths by date of occurrence for the period Quarter 1 2020 to the end of Quarter 2 2023. Deaths should be registered with the GRO within three months, however as noted above, the GRO's own analysis has found that on average approximately 82% of deaths are registered within this time frame. For this analysis a snapshot of all deaths registered with the GRO as of 03 July 2023, (one day after the end of the quarter), was taken and then compared with the data on death notices.

Figure 2: Comparison of death notices to officially registered deaths by date of occurrence

Figure 2 compares the number of death notices to the number of deaths registered with the GRO for each quarter up to 3rd July 2023. As expected, the number of deaths registered with the GRO for the latest quarter (Q2 2023) is significantly below the number of death notices on In this analysis the number of deaths registered is 40% below the number of death notices for the same quarter.

As we look further back in time and as more deaths are registered officially, the gap closes between the two sources. Data for Q2 2022, one year prior to the study, is broadly equal for the two sources. However, from approximately Q1 2021, over two years after some deaths occurred, there is a slight divergence between the two sources and officially registered deaths are in the region of 3 to 5% above the number of death notices. As it is unlikely that every single death has a death notice posted it would be expected that the official figures should eventually be higher than the number of death notices.

A possible explanation for why this only occurs two years after the death event may be related to the completion of the coroner court process and the issuance of a death certificate. The Coroner's Annual Returns 2022 noted that an inquest was held for 2,435 deaths in 2022. The Dublin District Coroner advised, as of August 2022, that inquests can take up to 24 months from the date of death to be heard. 

Table 1: Comparison between death notices and officially registered deaths over time.

Trends in Mortality over time

Figure 3: Combined Series - Registered Deaths 2000 - 2020 and Death Notices 2021 to 2023

Figure 3 examines mortality figures since 2000, with observed data forming the basis for cases from January 2021 to June 2023 and the older historical data coming from official CSO mortality figures by date of occurrence.

Within these years there are clear seasonal peaks, with the peak of deaths in January for all years with a notable exception in 2020 when the peak occured in April. There is also a clear trend from 2000 of yearly deaths falling slightly up to 2005, plateauing for a few years before rising again from 2011. Between 2010 (27,961) and 2020 (32,856) there was a 17% increase in annual deaths.

This long-term trend in mortality is broadly linked to the demographics of the Irish population specifically to the growth in the 65 years and over age group. (See Demography Trends)

Demographic Trends

Figure 4: Population 65 and over in April 1950 - 2023

Figure 4 shows the population 65 years or older since 1950. Between 1950 and 1970 this cohort grew at less than 1% each year. Between 1970 and 2006 annual growth was very steady at approximately 1% per year. Since 2007 this cohort has grown in the range of 2-5% per annum. This result of this growth means that since 2007 the population 65 or over has grown from 471,000 to 806,000 or in percentage terms, by 71%.

This growing cohort is important in the context of mortality figures, as for example in 2022, more than four-fifths (83%) of the deaths registered were persons aged 65 years or over. Source: Vital Statistics Yearly Summary 2022.

Figure 5: Projected Annual Deaths 2017 - 2030 (Pre-Census 2022 revisions)

Figure 5 graphs the projected annual deaths up to 2030 from the CSO Population and Labour Force Projections 2017 - 2051. These projections were completed after Census 2016 and are due to be revised based on Census 2022 data in the coming months. However, the graph demonstrates the overall trend in Ireland over the next number of years where the number of deaths will continue to rise in line with the aging population. 

Eurostat also produce population projections and breakdown the components. For 2022 the Eurostat baseline projection is 33,832 compared with the CSO projection of 32,877. The difference can be attributed to both different methodologies and also underlying data that has been updated and or extracted at different times.

Measuring Excess Mortality

The COVID-19 pandemic has highlighted the challenges in obtaining timely statistics on mortality and in particular, excess mortality (deaths over and above what would be expected under normal circumstances). Measuring the impact of such events on mortality trends can play an important role in policy and response efforts and in determining any additional impact on mortality related to the COVID-19 pandemic and its effects.

However, measurement of excess mortality is not straightforward and attributing trends to specific factors, in this study COVID-19, is particularly challenging. Measuring excess mortality, specifically where COVID-19 was a factor, would necessitate cleaning, classifying and linking each notice with the corresponding General Register Office (GRO) record which contains information about causes of death or contributory factors. This would need to be done for several previous years to identify and adjust external factors that may influence the number of notices placed.

What is Excess Mortality and how is it measured in this report?

Excess mortality measures the number of deaths over and above what would be expected under normal circumstances. Expected deaths are measured by calculating the average number of deaths for the same period in previous years. To get excess mortality we compare the deaths (or in this case death notices) in one period with the average of previous periods. In that sense excess mortality is an estimate. 

In previous releases we looked at a range of expected deaths (in the years just prior to the pandemic, 2016 to 2019) based on death notices published on In some studies, calculations of excess mortality look at an average of a greater number of years (e.g., a five year or 10-year average) and other studies focus on removing pandemic years and or adjusting for demographic factors. 

The CSO has since mid-2020 been providing Eurostat with estimated weekly deaths based on the methodology used in this release. Aligning this release with the work Eurostat has done on excess mortality allowed comparisons with other European countries however it is a simple method that does not account for demographic trends within individual countries.

As we move to the late/post pandemic period, statistical issues arise around calculating excess deaths particularly in attempting to define the baseline upon which to measure against. For the first full year of the pandemic, 2020, choosing a baseline was reasonably straight forward as deaths could be measured against an average of the immediately preceding years. However, as the pandemic continued, simple averages based on preceding years now include pandemic years and thus could distort the comparison. Similarly, excluding the pandemic years from the average removes or reduces the effect the aging population has on the baseline. For these reasons, exclusively using years 2016 to 2019 may no longer be an appropriate baseline for excess deaths from 2022 on.

In order to demonstrate the complexity around choosing a baseline, and to provide alternative scenarios, three different baselines have been calculated and used to calculate a range of excess deaths estimates.  See Background Notes. These baseline averages are:

  • 4-year average of 2016 to 2019
  • Average of the previous 4 years
  • Average of the previous 4 years but excluding 2020 data

What issues arise when using different baselines?

The 4-year average of 2016 to 2019: Using this baseline introduces a lag of between 3 and 7 years that strips out the existing trend of increasing deaths over time.

Average of the previous 4 years: A simple average of the previous 4 years includes the years of the pandemic when certain months had significant excess deaths. Comparisons with those months in 2023, particularly April, may now show negative excess deaths. 

Average of the previous 4 years but Excluding 2020 data: This baseline serves as a compromise between the two previous baselines. By excluding data from 2020, the effect of the most significant year of the pandemic is stripped out and a more realistic baseline for the peak months is provided, however an extra year’s lag is also introduced.

What can estimates of excess mortality tell us?

Estimates of excess mortality look at all causes of mortality during a period of observation, so the estimates of excess deaths are different to measurement of the number of deaths due to a particular cause (e.g., COVID-19 confirmed deaths). While COVID-19 confirmed deaths increased the level of excess mortality in the period, other causes may have had lower or higher impacts than in previous periods and none of these impacts can be disaggregated. Death notices, while having the advantage of timeliness, lack information on cause of death, and the age of the deceased, which is necessary to accurately profile mortality patterns over time.

COVID-19 confirmed deaths include people who died with and of COVID-19, which results in a different period total to all cause excess mortality, though the peak months are the same in both measures. Another difference between the two measures – i.e., excess deaths and deaths involving COVID-19 – is excess deaths can be negative, where deaths due to COVID-19 cannot be. 

Figure 6 - Excess Mortality

Figure 6 presents the three methods of calculating excess deaths on a single graph. For 2020 there is no difference in the three methods and there were eight months of positive excess deaths and four months of negative excess deaths. 

In 2021 two of the three methods presented the same outcome but the average of the previous four years shows lower excess deaths in months the March to May and August to November.

From 2022 on the variance in the methods becomes more obvious. While the trends are broadly similar the extent of excess deaths varies. The exception is December 2022 where all methods show excess deaths was in the region of 27-28%. 

For 2023 comparisons it is probable that the 2016:2019 baseline is over estimating excess deaths while the simple average of the previous four years may be underestimating. Using a 4-year average that excludes 2020 would seem to be a reasonable compromise for monitoring trends in mortality. Particularly in years so close to the peak of the pandemic and where deaths in recent years were already on the rise due to an aging population. 

In terms of the most appropriate baseline measure, the CSO will continue to give careful consideration to the methods presented above.