Teaching · For Teachers · Research and data

Same students, before and after:
did they really change?

Paste the two sets of scores in the same order. The calculator pairs them, ranks every change by size and tests whether the increases and decreases balance, with an exact p-value for small groups.

Run the testWhat you get
$12one-time · every device you sign in on
Buy · $12

Included with Caveat Classroom and Whole-school licenses. Or get it in the For Teachers toolkit, $79 for 72 items.

The signed-rank calculator

The worked example is made up: twelve readers timed before and after six weeks of repeated reading. Use codes, not names. Nothing you type leaves this browser.

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What you get

Teaching · For Teachers$12 · included with Classroom and Whole-school licenses

What you finish with
W+ and W−, the two-tailed p-value (exact or approximate, and which), the rank-biserial correlation, the median change, pairs up and down, and a table of every pair. It prints as a summary and downloads as a spreadsheet.
Who it is for
Teachers doing action research, reading and intervention specialists, school psychologists and graduate students in education.
Format
Browser calculator for a phone, tablet or computer, by touch or keyboard. Up to 500 pairs. Prints a summary; downloads a spreadsheet (.csv); export and import a file.
Access
$12 one-time, yours on every device you sign in on; the tool opens once you are signed in with it. Included with Caveat Classroom and Whole-school licenses. Also in the For Teachers toolkit ($79) and the Teaching Suite pass ($199), and 1 more bundle. Everything you type stays in this browser; nothing is sent to Caveat.
Where it lives
The For Teachers space in Caveat Teaching.
Support
Questions, a correction or a request: team@caveatacademic.com.

How to use it

  1. Name the measure and the two occasions.
  2. Paste the first scores and the second scores in the same student order.
  3. Read the p-value with the rank-biserial r and the median change.
  4. Check the pair table for a typing slip; a pair out of order changes everything.
  5. Print the summary or download the spreadsheet.

Run the test

How the test works

Each person against themselves, by rank.

The worked example: repeated readingDifferences12 pairsafter − beforeRank by size1 to 12ignore the signAdd ranks by signW+ 1W− 77Exact two-tailed< .001of 4,096 sign patternsThe worked example: repeated readingDifferences12 pairsafter − beforeRank by size1 to 12ignore the signAdd ranks by signW+ 1W− 77Exact two-tailed< .001of 4,096 sign patterns
Each reader is compared with themselves. Big changes get big ranks; if nothing were going on, the ranks of the increases and the decreases would come out about equal.

When to use it

The signed-rank test is the rank-based partner of the paired t-test. Use it for the same people measured twice when the changes are skewed, include outliers, or come from ratings and rubric levels. It uses both the direction and the size of each change, so it is more sensitive than simply counting ups and downs.

Reading the result

A small p says the changes lean one way more than chance would explain. With no comparison group, though, growth over six weeks can come from practice, maturity or a familiar passage as well as from the intervention, so report the design honestly. Pairs with no change are left out, as Wilcoxon proposed; the table shows which pairs were used.

Sources

  1. Wilcoxon, F. (1945). Individual comparisons by ranking methods. Biometrics Bulletin, 1(6), 80–83.
  2. Hollander, M., Wolfe, D. A., and Chicken, E. (2014). Nonparametric Statistical Methods (3rd ed.). Wiley. Chapter 3, the one-sample location problem.
  3. Kerby, D. S. (2014). The simple difference formula: an approach to teaching nonparametric correlation. Comprehensive Psychology, 3, 11.IT.3.1.
  4. Institute of Education Sciences, What Works Clearinghouse. Procedures and Standards Handbook, Version 5.0 (2022): pre-post designs and comparison groups.

The worked example is made up. Use student codes, not names. Your scores stay in this browser. Support: team@caveatacademic.com.