Guidelines for Reporting Statistics

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.

BUT κ=0.87

 

 

Percentages and decimal places

• If N<100, there is no decimal point in the percentage.
• If N is between 100 to 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 that..." should be revised to "the majority of participants (59/100, 59%) felt that..." NOT “the majority of participants (59%, 59/100) felt that..."

When the percentage is used 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%]). "

 

 

Chi-square test

• Authors must include the degrees of freedom; if not provided, you will be queried for these values during copyediting.
• Degrees of freedom are subscripted; the chi-square symbol is italicized.
• The chi-square value should be reported to only 1 decimal place.
• When reporting chi-square values in a table, include the degrees of freedom in parentheses: chi-square (df).
• The abbreviation for degrees of freedom (df) does not need to be expanded; it should be italicized (AMA glossary of statistical terms, section 19.5).

Examples:

In text: χ²₄=0.3

In table: Chi-square (df) à 0.3 (4)

 

 

Mean, standard deviation, standard error, and range

• Equal signs are not used; separate the value from the statistic with a space.

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?.

 

 

Odds ratio and confidence interval

• ORs should alwaysbe presented with CIs.
• Include 0 before the decimal point.
• 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:
• OR 1.2 (95% CI 0.9-2.4)
• OR 1.2% (95% CI 0.8%-1.6%)

95% CI –0.1 to 0.8

• …(odds ratio [OR] 2.92, 95% CI 2.36-3.62). 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%).

 

 

Interquartile range

• Include zero before the decimal point.
• Format as "IQR" followed by a hyphenated range (ie, no equal sign) or when presented alongside a median as "median (IQR)" and NOT as a single number indicating the difference between the 75th and 25th percentiles (AMA section 19.5).
• We prefer not indicating the 25th and 75th percentiles 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)...

 

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.
• The actual P value (P=...) should be expressed rather than a statement of inequality (eg, P<.05), unless P<.001 (eg, if P=.00005, change to P<.001; see exception below)
• 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 brief note for the authors when making the above changes
• The actual value of P should be expressed to two digits, whether or not it is significant (eg, P=.34, P=.02)
• If P<.01, P should be expressed to three digits (eg, P=.005)
• Three digits are acceptable if rounding would change the significance of a value (eg, P=.049 should not be rounded to P=.05 of P is considered significant at the ≤.05 level).

 

Formatting

• P is italicized and capitalized
  • Note: our typesetting scripts can convert the P to italics if the copyeditor forgets this.
• Do not use zero before the decimal point.

• Remove spaces before/after mathematical operators in P value expressions (eg, P< .001 should be changed to P<.001).
• In a table, the column heading should be “P value” not “P.” Note that "value" should not be italicized.
• All footnote symbols within a table are superscripted letters (a-z). The use of *, **, *** footnotes to mark significance levels (eg, *P<.05, **P<.01, ***P<.001) is discouraged. Authors are asked to provide exact P values instead. While we prefer the exact P values, there are exceptions to this general rule. The use of asterisks to indicate significance levels is allowed in the following instances:
  • 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)

Although the AMA (section 19.5) recommends that “[expressing] P to more than 3 significant digits does not add useful information to P<.001,” in certain types of studies (particularly GWAS [genome-wide association studies] and other studies in which there are adjustments for multiple comparisons, such as Bonferroni correction, and the definition of level of significance is substantially less than P<.05), it may be important to express P values to more significant digits. 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.”

If a study has a very large sample size, it may be necessary to report P values to a value smaller than P<.001 in order to show statistical significance. This will be up to editorial discretion.

“Trending” towards significance

• We do not use “trending towards significance” or other variants (eg, “There was a trend (P=.06) showing that…was significant”).
• It is fair to say that there was a trend in something, but this must be followed up with “…but these results were not statistically significant.”
• Alternatively, it is best to simply state the results’ significance and not use variations of “”

 

 

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

 

 

F test

• Include the degrees of freedom.
• F is italicized and degrees of freedom are subscripted in the text (F_#,#).
• In a table, degrees of freedom are included in parentheses after the number: F test (df).

Example: F_4,76=12.2

 

t test

• tis italicized and degrees of freedom are subscripted.
• Include zero before the decimal point.
• Authors must include whether the test is 1-tailed or 2-tailed.
• Authors must include the degrees of freedom; if not provided, these should be queried for during copyediting.
• In a table, the degrees of freedom are included in parentheses after the number: t test (df).

Example: t₁₅=2.68

 

 

Effect size

• Include zero before the decimal point.

Example: ...an effect size of 0.277 standard deviation units.

 

 

Cronbach alpha

• Do not use “Cronbach’s” α (ie, with the possessive; see “Additional guidelines” below for details).
• There is no zero before the decimal point.

Examples:

Cronbach α=.78

…a Cronbach α of .78

 

Cohen d

• Do not use “Cohen’s” d (ie, with the possessive).
• Include a zero before the decimal point if the value is less than 1.

Examples:

Cohen d=0.29

Cohen d=1.45

 

 

Beta level

• There is no zero before the decimal point.

Example: β=.2

 

 

Spearman rank correlation

• The symbol is ρ (rho) and it is not italicized.
• Include a zero before the decimal point if the value is less than 1.

Example: ρ=0.67

 

 

Pearson correlation coefficient

• The symbol is an italicized r.
• Include a zero before the decimal point.

Example: r=0.92

 

 

Kappa statistic

• The symbol is κ (not italicized).
• Include a zero before the decimal point if the value is less than 1.

Examples:

κ=0.51

The κ value indicating interobserver reliability was 0.5.

 

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”
• Hedges g: italicize “g” and do not use an apostrophe after “Hedges” or within the term as “Hedge’s g”
• I² for heterogeneity: use the 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

 

 

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

 

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:

y_i = C_i - c_i (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.