Let’s start at the most basic level. How should you express numbers in APA style? You actually have a lot of options. You could use Arabic numerals. You could spell out the numbers. Or you could even use Roman numerals. You could use four decimal places or two. You could use commas in large whole numbers or not. Below I list some rules to help you determine how to best report numbers in APA style.

Arabic Numerals

1. For numbers 10 and above use Arabic numerals. For numbers less than 10 write out the words.

The sample consisted of nine men and 10 women.

The pigeons were randomly assigned to one of three groups.

The results indicate that of the 13 different . . .

2. Never start a sentence using an Arabic numeral or a percentage.

Forty-five percent of the sample obtained the placebo.

Five respondents did not complete the entire procedure and were dropped from further analyses.

3. Use Arabic numerals in the abstract of a paper or in any graphical displays.

4. Use Arabic numerals when the number immediately precedes a unit of measurement.

Rats were given a 5-mg dose . . .

The comparison line was 11.70 cm.

5. Use Arabic numerals for numbers that represent statistical or mathematical functions, factional or decimal quantities, percentages, ratios, and percentiles.

There were 5 times as many men as women.

This number was then divided by 3 to determine . . .

We found that 5% of the respondents . . .

The mean age of respondents was 8.73 years.

6. Use Arabic numerals for dates, times, scores, money, points on a scale, and numerals.

The first cohort was born between the years of 1997 and 2000.

It was January 7, 2016.

At 12:30 AM an alarm was sounded . . .

Each child was given $5.

The first participant marked 4 on the 7-point scale.

7. Use Arabic numerals that denote a specific place in parts of a book, numbered series, and table.

Chapter 1 will cover . . .

Row 5 in Table 3 indicates . . .

Numbers Spelled Out as Words

Two rules were already presented above as to when you spell out the words.

8. Spell out whole numbers that are less than 10.

9. If a sentence begins with a number spell out the number. This extends to a title or text heading.

Eleven of the 15 participants . . .

It should be noted that often it is preferable to reword the sentence to avoid beginning with a number.

There are some exceptions to these rules.

10. Spell out commonly used fractions.

The results showed that two-thirds . . .

Over one half of the . . .

11. Spell out the number to conform to universally accepted conventions.

The Twelve Apostles . . .

The Five Pillars of Islam . . .

12. Use a combination of numeral and words to express back-to-back modifiers.

This rule is a little tricky because its use can violate some of the earlier rules. However, it is used to increase clarity and readability. To confuse things more this rule should not be mindless applied. It should only be used when it helps the reader more easily understand the material.

There were ten 5-point scales.

The results showed 2 two-way interactions were significant.

Here is an example of when it should not be used.

The 1st two items were . . .

It would be easier to read as shown below.

The first two items were . . .

Roman Numerals

13. Only use Roman numerals if they are part of established conventions.

In order to avoid increased Type II error rates . . .

The content of commercials from Super Bowl XLIX and Super Bowl L were compared.

Decimals

A common question is when should I use a leading zero before the decimal point? For example, should it be 0.05 or simply .05? The answer is it depends.

14. Only use a leading zero if the value could exceed 1.00.

If the value can never exceed 1.00 then a leading zero is not used. A couple of common statistical examples are correlations and p-values. A correlation can have a value of -1.00 to 1.00 and a p-value could range from zero to 1.00. Therefore, when writing results for correlations and p-values you would not use a leading zero.

There was a statistically significant difference (p < .05).

The correlation between job satisfaction and job performance was .23.

The mean score on the 3-point scale satisfaction scale was 0.99.

The length of the first line was 0.98 inches and the length of the second line was 1.02 inches.

Another common question concerning decimals is how many should I report?

15. Generally use two decimal places when reporting statistical results.

Two decimal places is the most commonly used convention when reporting statistical results. However, you should use as many decimal places as required to provide meaningful results with the appropriate level of precision.

For example, it does not make sense to include decimal places when the value can only take on whole numbers.

There were 89 participants.

Also, decimal places are commonly not used when reporting percentages.

In the resulting sample 68% were married, 20% divorced, 10% never married, and 2% widowed.

But this is not always the case.

A 0.5% solution was used . . .

There are situations where it may appear that more than three decimal places are required. For example, .003 cm. However, in this situation the number might be better written as 0.03 mm.

Rounding

After determining the appropriate number of decimal places to report you will often be required to round your results to get there.

16.  Use the conventional standards for rounding.

For example

.044 rounds to .04,
.045 rounds to .05,
.094 round to .09, and
.097 rounds to .10.

Comma in Numbers

17. Use commas between groups of three digits in numbers 1,000 or larger.

The sample consisted of 12,345 individuals who had retired within the past three months.

Like most rules, however, there are exceptions. Do not use commas when it would violate other rules or other commonly accepted conventions. For example, do not use commas in page numbers, binary numbers (011001011), serial numbers, temperature (1756 °F), or frequencies (1250 Hz).

Without going into detail here, often you will be required to report something called “degrees of freedom.” This is another case when you do not use commas.

The results of a one-way ANOVA was statistically significant, F(1, 1443) = 4.97, p < .01.

Test Yourself


1.     individuals participated in the study.

16
Sixteen

 

2. Mice were given     mg of gabapentin

5
five

 

3. Participants reported to the center at     and received   .

eight AM; five dollars
8:00 AM; $5

 

4. Generally, how many decimal places should you round to and report?

 One
 Two
 Three

 

5. When reporting decimal values when should you use a leading zero?

Always
Never
Only when the value could have been greater than 1.00