AMA Manual of Style - Stacy L. Christiansen, Cheryl Iverson 2020
Use of Digit Spans and Hyphens
Numbers and Percentages
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 2010-2012 National Health and Nutrition Examination 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 2010-2011 academic year.
Substantial profits were anticipated for fiscal years 2013-2015.
Helen B. Taussig, MD (1898-1986)
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, 2012, to September 1, 2014. (In this example, the enrollment period ended on August 31.)
Or: The second enrollment period spanned January 30, 2012, through September 1, 2014. (In this example, the enrollment period ended on September 1, 2014.)
We looked at the following 3 periods: 1985 through 1989, 1990 through 2000, and 2001 through 2014.
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 1990-2000 was approximately twice that during 2001-2014.
A hyphen may be used within parentheses or in tables to indicate spans, including CIs, 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 CIs), the word to should be used to avoid ambiguity (see 8.3, Hyphens and Dashes, and 19.4, Significant Digits and Rounding Numbers).
The mean number of years of life gained was 1.7 (95% CI, 1.3-2.1).
The mean number of years of disease-free life gained was 0.4 (95% CI, −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 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, the word 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.