During winter, hospitals expect more deaths.
With bad weather comes a greater chance of illness, particularly for the frail and elderly. Admissions are higher, putting pressure on accident and emergency departments and on the longer-term wards which require the capacity to house patients who need to be admitted.
It is an annual problem for the NHS. Patients' health problems can take longer to resolve but offering them quality care is harder due to the pressure placed on staffing and space.
New figures show that last year there were 453 more deaths in the winter of 2012/13 than during the winter period than in the previous year.
The figure was also higher than the winter of December 2010, despite the record low temperatures and extreme snowfall experienced that year.
The reason for this is not clear. The Scottish Government, which has targets to cut mortality rates, argues that hospital deaths in winter can vary for a range of reasons, including the prevalence of seasonal illnesses such as flu.
That may be the case. Doctors in A&E departments also wonder whether the chaos that affected many casualty units - with long waits and bed shortages - may also have been a factor.
Some point to the length of the winter - cold weather stretched on almost until May this year, and problems in some A&E units persisted for just as long. However although the winter was a long one, it was comparatively mild.
NHS Scotland clinical director Professor Jason Leitch argues that waits of more than 12 hours for hundreds of patients and the shortages of ward beds to transfer patients into will not have affected the mortality rate.
It is hard to see how he can be so sure. It is plain that the longer someone waits in an unsuitable setting the greater the likelihood that their care is compromised. The fact that elderly people in particular should not be in hospital any longer than is absolutely necessary is also well-established.
Rising death rates at two Lanarkshire hospitals are already under investigation, and need explanation.
But the figures revealed today are also a puzzle and until they can be explained, they appear worrying.
In addition, there has never been a clear or convincing explanation for the winter beds crisis last winter or why it was so significant and protracted.
These latest figures only serve to confirm the argument The Herald has been making through our NHS Time for Action campaign.
We have called for a review of capacity both in hospitals and community care services. Only a full review can ensure that the right staff and the right resources are in place to ensure social services and the NHS can cope with an ageing population.
Meanwhile the winter period is only a matter of weeks away. At the very least, the Scottish Government and NHS chiefs must be sure their plans are in place to prevent a repeat of last winter's turmoil in hospitals, in the interests of staff and patients alike.
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