# Evaluating Item Reliability In LearningSpace, a statistical number can help determine whether an item reflects the necessary knowledge and show the **correlation between certain answers** and [**Case total scores**](/doc/how-the-case-total-score-of-a-learner-is-calculated-GvIbMh2Yhe). # Point Biserial Value (PBS) The **Point Biserial (PBS)** value shows **how likely** it is that students who selected a certain answer for an item **would get a high overall score** in the Case. The value ranges from *-1 to +1*. The higher this value is, the higher the correlation between the answer and the Case total score. In LearningSpace, this value can be applied *either to the correct answer or to each answer*, depending on the [**Activity Reporting Setup**](/doc/aab64119-66b1-4c8f-95ed-95747f0918cb). If applied to the **correct answer**, the higher the point-biserial value, the "better" the item. That is, **reliable items have a high PBS value, meaning that they are selected by learners with high overall results in the Case. By contrast, items with low PBS values (below zero) tend to get selected by learners with weaker final results** in the Case. ![](https://outline-production-attachments.s3-accelerate.amazonaws.com/uploads/48ddf0a7-308b-4fe9-b28a-e3ce1797eaa8/82231dc2-219e-472d-838d-8f7c7e109595/12616032.png?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Content-Sha256=UNSIGNED-PAYLOAD&X-Amz-Credential=AKIA4EOUDTOVUICLPZ4P%2F20260909%2Fus-east-1%2Fs3%2Faws4_request&X-Amz-Date=20260909T120000Z&X-Amz-Expires=86400&X-Amz-Signature=8b6efe9353ccc6b1b7b864d657425c0a1ed38e7ad2db3b9de1561021a418b43e&X-Amz-SignedHeaders=host&x-amz-checksum-mode=ENABLED&x-id=GetObject "right-50 =358x48") **Mc** = Case total average for learners answering items correctly **Mi** = Case total average for learners answering items incorrectly **St** = [**standard deviation**](/doc/comparative-numbers-OM9w74zz3c) for the whole Case **c** = proportion of the learners in the learner group of the activity answering correctly **i** = proportion of the learners in the learner group of the activity answering incorrectly *__Example:__* 1. A checkbox item has three possible answers, with 1, 2, and 3-point answers. 2. There are 10 learners in the learner group. 3. Seven got the maximum 6 points, but they achieved only 60 percent as their Case total scores. 4. The other three members of the group achieved 3 points for the item, but they have 90 percent Case totals. 5. In this case, if the point-biserial (PBS) value is calculated for the "correct" answer of the item, and the answer is regarded as correct if the achieved point value for it is 100% of the max (set on the Activity Reporting Setup page), then the PBS is the following: ![](https://outline-production-attachments.s3-accelerate.amazonaws.com/uploads/48ddf0a7-308b-4fe9-b28a-e3ce1797eaa8/8938ca0b-cee1-412b-ba79-3894557bd377/12616033.png?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Content-Sha256=UNSIGNED-PAYLOAD&X-Amz-Credential=AKIA4EOUDTOVUICLPZ4P%2F20260909%2Fus-east-1%2Fs3%2Faws4_request&X-Amz-Date=20260909T120000Z&X-Amz-Expires=86400&X-Amz-Signature=0718bcc2f58d653590b37781ef69dcc960821b2c7580c7fceba25f9c95945c64&X-Amz-SignedHeaders=host&x-amz-checksum-mode=ENABLED&x-id=GetObject "right-50 =269x50") This shows that all learners with the "correct" answers for the item belong to the "bad" group, based on the Case Total Performance. It is obviously more complicated; however, the methodology is the same. On the [**Activity Reporting Setup**](/doc/report-formatting-BL3Xh0msVE) page, it can be determined if the "correct" answer(s) should be those that result in the maximum achievable point value for the item, or a certain portion of the maximum points should already be regarded as a correct answer. The maximum achievable score is obvious for questions with one possible answer choice, while for items with multiple possible answer choices (i.e., checkbox or scroll box questions), the maximum score is the sum of the achievable points for all the answers. ![](https://outline-production-attachments.s3-accelerate.amazonaws.com/uploads/48ddf0a7-308b-4fe9-b28a-e3ce1797eaa8/da0f1616-6ae2-4811-bb32-e372435c148b/76910010.png?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Content-Sha256=UNSIGNED-PAYLOAD&X-Amz-Credential=AKIA4EOUDTOVUICLPZ4P%2F20260909%2Fus-east-1%2Fs3%2Faws4_request&X-Amz-Date=20260909T120000Z&X-Amz-Expires=86400&X-Amz-Signature=0296ba971f5dfc58cd704452980522a50169d136761dfd051d1d043c4a1e3aca&X-Amz-SignedHeaders=host&x-amz-checksum-mode=ENABLED&x-id=GetObject "right-50 =358x234") The point-biserial value is displayed in the [**Case Item Analysis**](/doc/f5301a5d-f543-4412-a820-192b021bcafd). ![](https://outline-production-attachments.s3-accelerate.amazonaws.com/uploads/48ddf0a7-308b-4fe9-b28a-e3ce1797eaa8/e437de7e-be8e-425b-aeb5-f126708e1995/76909736.png?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Content-Sha256=UNSIGNED-PAYLOAD&X-Amz-Credential=AKIA4EOUDTOVUICLPZ4P%2F20260909%2Fus-east-1%2Fs3%2Faws4_request&X-Amz-Date=20260909T120000Z&X-Amz-Expires=86400&X-Amz-Signature=3af12834aca3bfe09d491dbf9c0523cf60555c121ac3f934c7a04a6dd26bf490&X-Amz-SignedHeaders=host&x-amz-checksum-mode=ENABLED&x-id=GetObject) :::tip For further information, see the [Reports - How to](/doc/reports-how-to-qnSWC08QSs) pages and the [Reports Module Training Videos](/doc/reports-module-training-videos-dr44xGB4HN). ::: --- **Documents** - [User Guide](https://kb.learningspace.elevatehealth.net/s/ent-hs/doc/user-guide-WPv4VxhtWB) - [FAQ](https://kb.learningspace.elevatehealth.net/s/ent-hs/doc/faq-YoxOQOjvnY) - [Training Videos](https://kb.learningspace.elevatehealth.net/s/ent-hs/doc/training-videos-D2ycsEwqPt) - [Module Introduction Videos](https://kb.learningspace.elevatehealth.net/s/ent-hs/doc/module-introduction-videos-I6OQ6H7SUT) - [Release Notes](https://kb.learningspace.elevatehealth.net/s/ent-hs/doc/release-notes-BcFFMsc0RV) - [Distance Learning with LearningSpace](https://kb.learningspace.elevatehealth.net/s/ent-hs/doc/distance-learning-with-learningspace-eAfwW23Hxg) - [Preventing Copy-Paste in LearningSpace](https://kb.learningspace.elevatehealth.net/s/ent-hs/doc/preventing-copy-paste-in-learningspace-sPD0IIUuk0) - [Important Technical Notification Regarding Adobe Flash Player](https://kb.learningspace.elevatehealth.net/s/ent-hs/doc/important-technical-notification-regarding-adobe-flash-player-eQtMLwLmTJ) - [iPad support - Technical information](https://kb.learningspace.elevatehealth.net/s/ent-hs/doc/ipad-support-technical-information-dLmeFvKofC) - [TeamViewer Link](https://kb.learningspace.elevatehealth.net/s/ent-hs/doc/teamviewer-link-QyKZBMqUT9) - [YouTube videos about LearningSpace](https://kb.learningspace.elevatehealth.net/s/ent-hs/doc/youtube-videos-about-learningspace-TMb3zdc0LC) - [Customer Aftercare One-Pager](https://kb.learningspace.elevatehealth.net/s/ent-hs/doc/customer-aftercare-one-pager-GBWMe1BcfS) - [Case Studies](https://kb.learningspace.elevatehealth.net/s/ent-hs/doc/case-studies-VcAbFqXSz7)