JMIR Publications employs professional external copyeditors (see What are the steps during copyediting? and What are the authors' responsibilities during copyediting?) to bring articles into editorial style, so authors do not have to worry too much about the style on initial submission, although it does shorten the production process after acceptance if the article is roughly aligned with our guidelines (see also JMIR's editorial guidelines).
While pointing out issues in statistical reporting is also a responsibility of the editor/section editor—who should point out missing statistics and incorrectly reported statistics already during the review process (and not rely on external peer-reviewers)—copyeditors act as the "second line of defense" and must enforce reporting in line with generally accepted guidelines. For details on common statistical terms, please refer to the AMA's Glossary of Statistical Terms. The recent SAMPL Reporting Guideline, which provides best practices on statistical reporting, is a useful resource for copyeditors.
Omission of leading zero
- We follow the guidelines set out by the AMA (sections 18.7.1 and 19.5).
- A zero should be placed before the decimal point for numbers less than 1, except when expressing the 3 values related to probability: P, α, and β. These values cannot equal 1, except when rounding. Because they appear frequently, eliminating the zero can save substantial space in tables and text. (Although other statistical values also may never equal 1, their use is less frequent; to simplify usage, the zero before the decimal point is included.)
Examples:
P=.16
1 − β=.80
Our predetermined α level was .05.
- Sometimes α and β are used to indicate other statistics (eg, Cronbach α or β coefficient), which may have values ≥1. In these cases, a leading zero is necessary.
N and n
- N designates the entire population under study.
- n designates a sample of the population under study.
- Do not insert spaces before and after the sign, and delete spaces on either sides of mathematical operators, except in equations.
Examples: N=468, n=234
Percentages and decimal places
- If N<100, there is no decimal point in the percentage.
- If N is between 100 and 999, 1 decimal point is reported.
- If N≥1000, 2 decimal points are preferred, but 1 decimal point is acceptable.
- BUT if a table contains mixed denominators, be consistent and use, for example, 1 decimal point consistently even if some denominators are less than 100.
- Do not add a zero after the decimal if the percentage value is a whole number (ie, 64/100=64%, not 64.0%). There are no exceptions to this guideline.
- Note: When rounding significant digits, if the digit immediately to the right of the last significant digit is 5, with either no digits or all zeros after the 5, the last significant digit is rounded up if it is odd and not changed if it is even (eg, 47.75 is rounded to 47.8, but 47.65 is rounded to 47.6; AMA section 19.4.2).
- See AMA 18.7.1, 18.7.2, and 18.7.3
Examples:
If N=87, use 45%
If N=356, use 45.1%
If N=1024, use 45.13%
Percentages within a sentence
- Preferred JMIR style is to always make clear what the numerator and denominator associated with a percentage are.
Example I:
"the majority of participants (59%) felt..." OR “the majority of participants (59%, 59/100) felt..."
should be revised as follows:
"the majority of participants (59/100, 59%) felt..."
When the percentage is emphasized in the sentence:
"…where 59% (59/100) of the participants felt that…"
Example II:
"a vast majority (n=488, 88.7%) of participants"
should be changed as follows:
"a vast majority (488/550, 88.7%)" (Note: The "n=" has been dropped and the "N" value, that is, 550, has been added).
- In expressing a series of proportions or percentages drawn from the same sample, the denominator need be provided only once.
Example: Of the 200 patients, 6 (3%) died, 18 (9%) experienced an adverse event, and 22 (11%) were lost to follow-up.
- Do not use square brackets within parentheses for statistics. Separate values with a comma if statistics are linked (eg, % and numerator/denominator); separate values with a semicolon if statistics are unlinked (eg, % and odds ratio).
Examples:
“a vast majority (488/550, 88.7%; P=.002)”
“…were not significant (P=.50; OR 2.72, 95% CI 0.45-2.6)”
WRONG:
"The most common functions among studies that involved children with special needs were consultation (8 studies [73%]) and diagnosis (7 studies [64%]). "
Mean, standard deviation, standard error, and range
- Equal signs are not used; separate the value from the statistic with a space.
- The SD should always be displayed along with mean values; preferred format: mean (SD)
Examples:
mean 4.71 (SD 0.47) cm; mean 35% (SD 4.3%)
range 4-5
SE 2.55
...were aged 20 to 69 years (mean 38.9, SD 11.1 years)
- When reporting multiple statistics in a sentence, use a semicolon to separate the unrelated items.
Example: “The age (in years) of the participants (mean 4.71, SD 0.47; range 4-5)...”
- For mean (SD), we prefer not to use the ± Instead, an expression like 1.11 ± 2.33 should be formatted as "1.11 (SD 2.33)." Authors are advised to review such changes made by your copyeditor. Copyeditors are advised to add a query notifying the author(s) of this change, in case there are other statistics that have also been formatted by authors with a ± sign (eg, SE) and they now need to specify the expression.
- When reporting a value that is calculated from a mean and SD value, report it in the following manner: mean + SD = 6
- When reporting mean and SD in a table, include both values in the same column. The column or row header should include the wording “mean (SD)” after the variable name.
Example: Age (years), mean (SD)
- As of December 4, 2013, AMA no longer requires the expansion of "SD" or "SE" in the text (section 19.6). Also see Which abbreviations don't need to be expanded?.
Median and interquartile range
- Equal signs are not used; separate the value from the statistic with a space.
- The interquartile range (IQR)—distance between the 25th and 75th percentiles—should be displayed along with median values; preferred format: median (IQR).
- Include the leading zero before the decimal point for values <1.
- Do not format as a single number indicating the difference between the 75th and 25th percentiles (AMA section 19.5).
- We prefer indicating the 25th and 75th percentiles as a hyphenated range, not as comma-separated values.
- IQR does not need to be expanded.
Examples:
A median value of 54 (IQR 45-62)...
The median (IQR) was 54 (45-62)...
Odds ratio and confidence intervals
- ORs should always be presented with CIs.
- Include the leading zero before the decimal point for values <1.
- If one value in the CI range is negative, then “to” should be used rather than a hyphen. If this occurs in a table, replace the hyphen in all ranges in that table for consistent presentation.
- Avoid brackets within parentheses. If brackets within parentheses are necessary, use square brackets. In addition, avoid using parentheses inside another set of parentheses altogether; eg, (OR 2.92 (2.36-3.62)) should be rewritten as (OR 2.92, 95% CI 2.36-3.62).
- CI does not need to be expanded (AMA section 19.6; also see Which abbreviations don't need to be expanded?).
- When defining “OR” within parentheses, use square brackets.
Examples:
- The odds ratio was 3.1 (95% CI 2.2-4.8).
- OR 1.2% (95% CI 0.8%-1.6%)
- …(odds ratio [OR] 2.92, 95% CI –0.1 to 0.8). Note that OR needs to be defined in tables (through a footnote or in the caption).
Confidence limit
- Report the upper and lower boundaries of the confidence limit with a comma separating the 2 values.
Example:
The mean (95% confidence limits) was 30% (28%, 32%).
P value
From our instructions for authors:
Reporting
(Again, this is the primary responsibility of the academic editor, but the copyeditor acts as a second line of defense if this has been overlooked by the editor/section editor.)
- Note for copyeditors: point the author to the relevant section in the Instructions for Authors if P values are missing (ie, stating "no significant differences were found..." without reporting the P level), incorrectly reported, or replaced by statements of inequality (or asterisks in tables instead of exact values) such as P<.05.
- Ensure P values are present and correctly reported rather than a statement of inequality (eg, P<.05), unless P<.001 (eg, if P=.00005, change to P<.001; see exception below).
- Express specific P values as decimals (eg, P=.34).
- P values cannot be 0 or 1
- If reported as P=0, change to P<.001
- If reported as P=1, change to P>.99
- Copyeditors should leave a note for authors when making such changes.
- Use two-digit precision for most P values.
- Use three digits for P<.01 and when rounding affects significance.
Examples:
- P=.005
- P=.0027 rounded off to P=.003
- P=.049 should not be rounded to P=.05 (P is considered significant at the ≤.05 level).
Formatting
- Italicize and capitalize "P"
- Note: our typesetting scripts can convert the P to italics if the copyeditor forgets this.
- Do not use leading zero before the decimal point.
- Remove spaces around mathematical operators in P values (eg, P< .001 → P<.001).
- In tables, use "P value" as the column heading (not just "P").
- Use superscripted letters (a-z) for table footnote symbols.
- Use of asterisks as footnotes to indicate significance levels is discouraged (eg, *P<.05, **P<.01, ***P<.001). Authors are asked to provide exact P values instead.
- Exceptions to the use of asterisks to indicate significance levels include:
- In tables of systematic reviews, which tend to be busy and where the original P values can't be found in the original publications
- When odds ratios instead of P values are presented
- If for any reason the authors are unable to provide the exact P values
P values for very large sample sizes (according to AMA guidelines)
- Express P values to the level required by the study's significance threshold.
- Although the AMA (section 19.5) recommends that “[expressing] P to more than 3 significant digits does not add useful information to P<.001,” but in specific cases, such as GWAS (genome-wide association studies), studies using adjustments like Bonferroni correction, or studies with stringent significance thresholds, more digits may be needed.
- For example, if the threshold of significance is P<.0004, then by definition the P value must be expressed to at least 4 digits to indicate whether a result is statistically significant. GWAS express P values to very small numbers, using scientific notation. If a manuscript you are editing defines statistical significance as a P value substantially less than .05, possibly even using scientific notation to express P values to very small numbers, it is best to retain the values as the author presents them.
- For very large sample sizes, it may be necessary to report P values to a value smaller than P<.001 in order to show statistical significance, at the editor's discretion.
“Trending” towards significance
- Avoid phrases like "trending towards significance." (eg, “There was a trend (P=.06) showing that…was significant”).
- Instead, state if there was a trend, followed by acknowledging that the results were not statistically significant. Alternatively, clearly state the results' significance without using variations of "trending."
Guidance on formatting common statistical measures
| Statistic | Guidelines | Zero before decimal | Example |
|---|---|---|---|
| F test |
|
Yes |
Text: F4,76=12.2 Table header: F test (df) –> 12.2 (4, 76) |
| t test |
|
Yes |
Text: t15=2.68 Table header: t test (df) –> 2.68 (15) |
| Effect size | — | Yes | ...an effect size of 0.277 SD units. |
| α level | — | No |
Our predetermined α level was .05. |
| Cronbach α |
|
Yes |
Cronbach α=0.78 |
| Cohen d |
|
Yes |
Cohen d=0.29 Cohen d=1.45 |
|
Hedges g |
|
Yes | |
| β (beta) | — | No | β=.2 |
| β coefficient | — | Yes | Standardized β coefficient=2.34 |
| Spearman rank correlation |
|
Yes | ρ=0.67 |
| Pearson correlation coefficient |
|
Yes | r=0.92 |
| Kappa statistic |
|
Yes | κ=0.51 |
| Chi-square test |
|
Yes |
Text: χ24=0.3 Table header: Chi-square (df) –> 0.3 (4) |
Other statistics
Formatting rules for additional statistics are specified below:
- F1-score: italicize “F,” place “1” as a subscript, use a hyphen before “score,” and start “score” with a lowercase “s”
- I2 for heterogeneity: use an uppercase italicized “I”
- Type I error and type II error: do not use the numerals 1 and 2; AMA section 19.5
- R2: use the uppercase italicized “R”; do not italicize the superscript
- z score: lowercase italicized "z" without a hyphen
Additional guidelines
Eponyms
- Do not use possessives for the name of any statistical test (see Use of possessives with eponyms and AMA section 15.2).
Example: Hedges g (instead of Hedges’ g)
Equal and inequality signs
- For greater than or equal to (≥) and less than or equal to (≤) signs, insert a single symbol using MS Word
- Mac shortcuts: option + > = ≥ and option + < = ≤
- Windows shortcuts: ALT + 8805 = ≥ and ALT + 8804 = ≤
- Do not use an underlined greater than/less than symbol.
Example: y≤0
Exponents
- For very small or large numbers (eg, P values), do not precede the exponent with “e” or “^”. Superscript the exponent.
- Use an en dash to indicate negative exponents.
- For more information, refer to the AMA (section 20.3).
Examples:
2 × 106
10 × 3–10
m⋅s−1
Greek letters in text
- Use of Greek letters rather than spelled-out words is preferred per AMA guidelines, unless common usage dictates otherwise.
- In titles, subtitles, headings, and at the beginning of sentences, the first non-Greek letter after a lowercase Greek letter should be capitalized.
Examples:
Cronbach α
Beta-thalassemia
tau protein
β-Blockers help control heart rate...
Currency
- Specify all currencies in US$. For amounts reported in non-US currency, the current exchange rate should be used to calculate the amount in US dollars, and that amount should be shown in parentheses.
- If there are more than 10 instances of another currency presented, a blanket statement of the exchange rate from the original currency to US$ should be included: "A currency exchange rate of CAD $1=US $0.72 is applicable." This rate should be the current conversion rate and is available online here: https://www1.oanda.com/currency/converter/(AMA-recommended resource). You can directly add this into the manuscript (and ask the author to verify) or ask the author to add it in for you.
- For all currency measures, refer to the 11th edition of the AMA here: https://www.amamanualofstyle.com/view/10.1093/jama/9780190246556.001.0001/med-9780190246556-chapter-17-div2-34?rskey=z4zEI1&result=1.
- Do not use zeros after whole numbers of currency.
Examples:
US $99
CAD $125.35
€40
Aus $100 (Note: AMA uses "A$" for Australian dollars, but since we use a space before the $, this would be confusing as "A $100"; therefore, we'll abbreviate to "Aus $")
Each participant was rewarded with Amazon gift cards worth CAD $5 (US $7.18) for their participation.
Equations
In the text, whenever possible, characters in equations should be inserted using the Advanced Symbols feature of MS Word. Equations can be inserted within a paragraph (in line with the text) or on a separate line. Do not use the equation editor/tools in Word; the special formatting will not be picked up by our scripts.
Simple equations that are kept in text should be indented and numbered (number in bold) in parenthesis after the equation itself if they meet the following criteria: (1) if there are numerous equations (3 or more) in a manuscript, (2) if the equations are related to each other, or (3) if the equations are referred to after initial presentation (eg, Per equation 3, we recalculated…).
Example:
yi = Ci - ci (1)
Use spaces between all mathematical operators in complex equations (including “=”). Note in this case, “=” is functioning as an operator; it is not a statement of equality. In the case of “n=2,” no spaces are used as it is a statement of equality.
Guidelines for formatting complex equations can be found here.
Forest plots
Meta-analyses and systematic reviews often contain forest plots to summarize their results—these display individual study results (tabularly) and, usually, the weighted mean of studies (graphically) included in a meta-analysis focused on a specific outcome. For details, see chapter 4.2.1.11 in the AMA Manual of Style (11th edition). Shown below are 2 ways in which a forest plot can be presented.
(1) As a table:
Table 1. Forest plot of 2 studies comparing the effectiveness of serious games with that of conventional exercises on verbal learning.
(2) As a figure:
Figure 1. Forest plot of 6 studies comparing the effectiveness of serious games with that of no or sham interventions on verbal learning [29,30,31-34].