# What is the meaning of * or ** or *** in reports of statistical significance from Prism or InStat?

# Choose P value Format

Starting with Prism 8, Prism allows you to choose which decimal format Prism will use to report P values (information on previous versions of Prism can be found below). Each analysis that computes P values gives you four choices:

- APA (American Psychological Association) style, which shows three digits but omits the leading zero (.123). P values less than 0.001 shown as "< .001". All P values less than 0.001 are summarized with three asterisks, with no possibility of four asterisks.
- NEJM (New England Journal of Medicine) style, which shows three digits and includes the leading zero (0.123). P values less than 0.001 shown as "< .001". All P values less than 0.001 are summarized with three asterisks, with no possibility of four asterisks.
- GraphPad style which reports four digits after the decimal point with a leading zero (0.1234). P values less than 0.0001 shown as "< .0001". P values less than 0.001 are summarized with three asterisks, and P values less than 0.0001 are summarized with four asterisks.
- Choose how many digits you want to see after the decimal point, up to 15. P values less than 0.001 are given three asterisks, and P values less than 0.0001 are given four asterisks.

Symbol |
Meaning |

ns |
P > 0.05 |

* |
P ≤ 0.05 |

** |
P ≤ 0.01 |

*** |
P ≤ 0.001 |

**** |
P ≤ 0.0001 (For the last two choices only) |

Note that the first two choices (APA and NEJM) show at most three asterisks (***) and the last two choices will show four asterisks with tiny P values (****).

The multiple t test analysis is different than all the rest. The "Significant?" column has a single asterisk if the t test for that row is statistically significant, given your setting for alpha and the correction for multiple comparisons. Prism either places a single asterisk in that column or leaves it blank. It never places more than one asterisk there.

# Prism 6 and InStat 3

Prism 6 uses this convention:

Symbol | Meaning |

ns | P > 0.05 |

* | P ≤ 0.05 |

** | P ≤ 0.01 |

*** | P ≤ 0.001 |

**** | P ≤ 0.0001 (see note) |

Up to three asterisks, this is fairly standard, but not completely, so you ought to state the scale in your figure legends or methods section. Four asterisks for tiny P values is not entirely standard.

# Prism 5

Up until Prism 5.04 (Windows) and 5.0d (Mac), Prism never reported more than three asterisks. Any P value less than 0.001 was designated with three (***) asterisks.

With Prism 5.04 and 5.0d, P values between 0.0001 and 0.001 are shown with three asterisks, and P values less than 0.0001 are shown with four (****) asterisks.

# <0.05 or <=0.05?

Prism has always used the less-than-or-equal-to inequality. Until May 2012, this page mistakenly said the cutoff was less-than...

Prism makes the decision on whether to display an asterisk (and how many asterisk to show) based on the full P value it computes in double precision (about 12 digits of precision), not the P value you see displayed. So if the P value is actually 0.0500001, Prism will display "0.0500" and label that comparison as "ns".

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