Also, Sweden has a peculiar bookkeeping system, and a surprisingly large number of deaths are recorded without precisely known date. If you only look at weekly death statistics, you will miss the "week 99" deaths from the yearly total.
And here you would assume very wrong.
OECD does indeed estimate excess mortality simply by comparing to the 2015-2019 averages:
"The expected number of deaths is based on the average number of deaths for the same week over recent years (in this case the previous five years, 2015-19). This baseline could be considered a lower estimate of the expected number of deaths since both population growth and an ageing population would be expected to push up the number of deaths observed each year."
"Importantly, given the impact of COVID-19 to the overall number of weekly deaths in 2020, the average deaths for the period 2015-2019 continues to be used to calculate excess deaths in 2021, and still applies as the base for 2022 and 2023 excess deaths."
From their: Methodology_All-cause-Excess-and-COVID-19-deaths_OECD.pdf
Which you can find from https://stats.oecd.org/index.aspx?queryid=104676 when you try to find their notes for methodology.
Also here you are assuming somewhat wrong.
For Finland, the 2015–2019 average annual deaths is 53723. 2022 deaths were 63219. Thus the simple, OECD-style, estimate for excess mortality is 9496.
Whereas an age-structured model from Statistics Finland estimated 56158 deaths for 2022 from pre-covid trends. So the age-structure-aware excess mortality estimate is 7061 for 2022 for Finland.
https://ourworldindata.org/grapher/excess-mortality-raw-deat...
https://ourworldindata.org/grapher/excess-mortality-raw-deat...
April 2020 did a real number on that country...
https://i.imgur.com/X6BKdnt.png
Sweden was the only country where the result was clearly distinguishable from noise...
It's also important to remember in all this that the lockdown policy wasn't predicated on making a small difference you need powerful statistics to find. It was advertised as: anyone who doesn't lock down will experience mass deaths and full blown collapse. Epidemiologists claimed Sweden would experience double the usual death rate due to COVID, i.e. as many deaths from COVID as from all other causes combined! Their actual death rate:
https://www.statista.com/statistics/525353/sweden-number-of-...
There's a tiny bump in 2020, but at least part of that is simply noise due to 2019 having an unusually low death rate, so you'd expect it to be higher than normal in 2020 even without COVID.