National Records of Scotland

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Increased Winter Mortality in Scotland, 2007/08

Increased Winter Mortality in Scotland, 2007/08

29 October 2008

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Background

Many studies have shown that mortality levels in Scotland are markedly higher in winter months than summer months. Moreover, there are indications that this increased winter mortality has been relatively high in Scotland (and the rest of the UK) when compared with many countries with more extreme winter climates, though UK levels are comparable to several southern European countries (e.g. Greece, Italy, Spain) and lower than those recorded in Portugal and the Republic of Ireland. Whilst a number of theories have been advanced to explain these observations, there is as yet no consensus on the underlying mechanisms involved.

In 2002, National Records of Scotland (NRS) published an Occasional Paper entitled ‘The Raised Incidence of Winter Deaths’.  As well as reviewing the various definitions used to assess the extent of increased winter mortality, this paper showed that additional winter deaths were particularly associated with respiratory and circulatory diseases and that few deaths were caused by hypothermia. It also demonstrated that, though not all increased winter mortality is related to influenza, there was a clear link between the number of additional deaths and the level of influenza activity.

For the purpose of the statistics reported here, increased winter mortality is defined as the difference between the number of deaths in the four-month 'winter' period (December – March, inclusive) and the average number of deaths in the two four-month periods which precede winter (August – November) and follow winter (April – July).

Results

Table 1 summarises recent trends for Scotland. Provisional data show that there were some 2,180 'additional' deaths in Scotland during the winter of 2007/08. This is almost 600 fewer than during the previous winter, and is the fifth lowest figure in the 57 years for which such statistics are provided (in Table 2 and Chart 1). 

The winter of 2005/06, with mild weather and no serious outbreaks of 'flu', had the lowest number of 'additional' deaths (1,780) recorded since the series started in 1951/52; the winter of 2001/02 had the second lowest figure (1,840), so the latest seven years account for three of the five lowest figures in the past 57 years.  The number of 'additional' deaths in winter 2007/08 was around two-fifths (42%) of the figure for 1999/2000, the last time influenza activity was at a high level.

Table 1 also shows the extent to which the winter increase in mortality affects the elderly, particularly those aged 75 and over.

Chart 1 shows the increased winter mortality figures for the past 50-or-so years individually (the bars) and in the form of a 5-year moving average (which should give a better guide to the overall trend, as it 'smoothes out' most - but not all - of the effect of the year-to-year fluctuations in the figures).  The chart shows that there has been an overall downward trend in the number of 'additional' winter deaths over the past 50-or-so years: although there have been unusually high numbers in some years (which generally coincide with periods of high influenza activity), the height of the peaks appears to be falling, and the value of the 5-year moving average is tending to decline.  However, there are fluctuations around the overall long-term downward trend, such as the rise in the moving average towards the end of the 1990s.  Table 2 gives the underlying figures for Chart 1.

Table 3 gives a more detailed breakdown by age and NHS Board area, and Table 4 shows the underlying data (death registrations) used to calculate the seasonal increases in deaths.

Revisions to previously-published figures: Some minor revisions have been made to the previously-published figures for 2006/07 (which were described as provisional) and 2005/06.  In addition, in Table 3, the Increased Winter Mortality Index values now appear as whole numbers (rather than with one decimal place), given the approximate nature of the estimates (the corresponding numbers are rounded to the nearest ten).

Corrections to previously-published figures: This year, the figures were calculated using different software, and checked against last year's results.  It was found that many of the previously-published figures for 75-84 year olds for Highland and Greater Glasgow & Clyde were wrong: they had not been adjusted properly to include deaths in the relevant parts of the former Argyll & Clyde Health Board area.  Those figures have been corrected in the tables provided below (those areas' figures for the other age-groups were correct).

Note:   
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Table 1

Increased winter mortality by age group, Scotland, 1990/91 to 2007/08
(Excel    CSV    PDF)

Table 2

Increased winter mortality, Scotland, 1951/52 - 2007/08
(Excel    CSV    PDF)

Table 3

Increased winter mortality and increased winter mortality index, by age group and NHS Board area of usual residence, 1999/2000 to 2007/08
(Excel    CSV    PDF)

Table 4

Increased winter mortality - underlying death registrations, Scotland, 1990/91 to 2007/08
(Excel    CSV    PDF)

Chart 1

Increased winter mortality, Scotland, 1951/52 to 2007/08
(Excel    PDF)

Statistical Service in Scotland