Use of Digit Spans and Hyphens
Digits should not be omitted when indicating a span of years or page numbers in the text. Hyphens may be used in text when a year span is used as the identifying characteristic of a study (eg, the 1982–1984 NHANES survey), but only when the actual dates of the study have been defined previously in the text; if the dates are not defined in the text, the hyphen is ambiguous and may or may not mean that the dates indicated are inclusive. In certain circumstances, such as fiscal year or academic year, the actual span may be understood and no definition is required; in these cases the hyphen is acceptable at first mention and throughout the text.
The students participated in the study during the 1994–1995 academic year.
Substantial profits were anticipated for fiscal years 1996–1998.
Sir William Osler (1849–1919)
Use of to also may introduce ambiguity. To should be used rather than through only when the final digit is not included in the span and through instead of to when the final digit is included in the span. However, in some circumstances, such as life span, historical periods, fiscal or academic year, page numbers in text, or age ranges, the meaning is clear without making a distinction between to and through, and to may be used.
The participants ranged in age from 23 to 56 years.
The second enrollment period spanned January 30, 1991, to September 1, 1993. [In this example, the enrollment period ended on August 31.]
Or: The second enrollment period spanned January 31, 1991, through August 31, 1993.
We looked at the following 3 periods: 1964 through 1967, 1968 through 1978, and 1979 through 1992.
Time spans may be referred to by means of hyphens between years once the meaning has been made clear at the first mention.
The mortality rate ratio of 2.01 (95% CI, 1.80-2.24) indicates that the mortality rate during 1968–1978 was about twice that during 1979–1992.
A hyphen may be used within parentheses or in tables to indicate spans, including confidence intervals, without further definition, provided the meaning is clear. However, if one of the values in the span includes a minus sign (most commonly found in confidence intervals), the word to should be used to avoid ambiguity. The word to should then be used in place of the hyphen throughout the table and text for consistency. (See also 8.3, Punctuation, Hyphens and Dashes, and 20.8, Study Design and Statistics, Significant Digits and Rounding Numbers.)
The mean number of years of life gained was 1.7 (95% confidence interval, 1.3-2.1).
The mean number of years of disease-free life gained was 0.4 (95% confidence interval,−0.1 to 0.9).
After the drug was injected, the seizures continued for a brief period (20-30 seconds), then ceased.
The fourth edition contains a discussion of recommended preventive measures (pp 1243–1296).
The median age of the individuals in the sample was 56 years (range, 31–92 years).
If the unit of measure for the quantity is set closed up with the number, the unit should be repeated for each number.
The temperature remained normal throughout the day (96.5°C-97.3°C).
The differences between groups were relatively small (5%-8%).
But: The pressure gradient varied widely (10-60 mm Hg) throughout the day.
If the unit of measure changes within the parentheses, to is used.
Because of the wide range of measurements (2 mg to 3.7 × 104 kg), we displayed our results on a logarithmic scale.