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Table 1 Advantages and disadvantages of using an excess winter mortality index to determine wintertime health burdens

From: Health effects of milder winters: a review of evidence from the United Kingdom

Advantages: Disadvantages:
• It is easy and quick to calculate. If daily or even seasonal mortality counts are available, the formula can be applied without advanced statistical methods.
• It is readily understood by the lay public and policymakers.
• It can measure the full excess at wintertime, without missing many deaths due to delayed effects.
• It is crude. Seasonal changes in health do not occur according to fixed calendar dates.
• Not all deaths due to cold are during the winter, and not all of the winter excess is due to cold.
• International comparisons are complicated by potential differences in the distribution of wintertime deaths and the length of the winter period.
• The ratio may be sensitive to the periods used in the denominator, e.g. if summer months are included the occurrence of a heat-wave may artificially reduce the index.
• It doesn’t allow for identification of which weather factors are important for health or for the specific conditions, e.g. are cold-spells occurring early in the winter worse than later ones?