Statistics How To

Standardized Test Statistic: What is it?

Hypothesis Testing > What is a Standardized Test Statistic?

Standardized Test Statistic Formula

If you’re taking the AP Statistics test, you’ll need to know the general formula for a standardized test statistic. Standardized test statistics are used in hypothesis testing. The general formula formula is:

Standardized test statistic: (statistic-parameter)/(standard deviation of the statistic).

The formula by itself doesn’t mean much, unless you also know the three major forms of the equation for z-scores and t-scores.

How to use these formulas: All of the formulas require you to insert three pieces of information:

  1. Your test statistic. For example, the median.
  2. The known population parameter.
  3. The standard deviation for the statistic.

Standardized test statistic for z-scores

z score formula
For easy steps on how to solve this formula, see: How to calculate a z-score.

T-score (single population)

standardized test statistic
For easy steps on how to solve this formula, see: What is a T Score Formula?

T-score (two populations)

t-score two populations

What does a Standardized Test Statistic mean?

Standardized test statistics are a way for you to compare your results to a “normal” population. Z-scores and t-scores are very similar, although the t-distribution is a little shorter and fatter than the normal distribution. They both do the same thing. In elementary statistics, you’ll start by using a z-score. As you progress, you’ll use t-scores for small populations. In general, you must know the standard deviation of your population and the sample size must be greater than 30 in order for you to be able to use a z-score. Otherwise, use a t-score. See: T-score vs. z-score.

Calculating a Standardized Test Statistic: Sample Problem

The mean life of a particular battery is 75 hours. A sample of 9 light bulbs is chosen and found to have a standard deviation of 10 hours and a mean of 80 hours. Find the standardized test statistic.

The population standard deviation isn’t known, so I’m going to use the t-score formula.

Step 1: Plug the information into the formula and solve:
x̄ = sample mean = 80
μ0 = population mean = 75
s = sample standard deviation = 10
n = sample size = 9

t = 80-75 / (10/√9) = 1.5.

This means that the standardized test statistic (in this case, the t-score) is 1.5.

Check out our YouTube channel for more stats help and tips!


If you prefer an online interactive environment to learn R and statistics, this free R Tutorial by Datacamp is a great way to get started. If you're are somewhat comfortable with R and are interested in going deeper into Statistics, try this Statistics with R track.

Comments are now closed for this post. Need help or want to post a correction? Please post a comment on our Facebook page and I'll do my best to help!
Standardized Test Statistic: What is it? was last modified: January 10th, 2018 by Stephanie

2 thoughts on “Standardized Test Statistic: What is it?

  1. Brittney

    What’s the calculator shortcut for this? It’d be a bit more useful in a college stats class.