Every result in the RRB ALP psycho test, the Computer Based Aptitude Test (CBAT), is a T-Score, not a count of right answers. You need a T-Score of 42 or more in each of the five tests to qualify, and the five T-Scores together give a score out of 30 that goes into the final ALP merit. RDSO, the Research Designs and Standards Organisation of Indian Railways, designs the test, and its FAQ for candidates gives the formula and three worked examples. This article walks through them, in RDSO's own figures, and then says what they mean for the way you prepare.
If you are new to the exam, read the complete guide to the RRB ALP psycho test first. It explains the five tests and the 20 kinds of question the hall can give. On the Kautilya Classes portal, every practice paper and every Full Mock reports this same T-Score, computed the same way, so the number you see in practice is the number that matters in the hall.
RDSO's answer to "what is the criterion to qualify" is short: a T-Score of 42 or more in each test, and the T-Score is different from the raw score. The raw score of each test is converted into a T-Score. The conversion compares you with everyone who sat that test. So the T-Score does not say how many you got right; it says where you stand in the group. Five tests, five groups, five T-Scores. Each one must clear 42 on its own.
T = 50 + 10 × (x − Mean) ÷ SD, where x is your score in the test, Mean is the average score of all candidates who appeared in that test, and SD is the standard deviation of their scores.
Two numbers describe the group. The mean is the average score. The standard deviation (SD) says how spread out the scores are: a small SD means most candidates scored close to the mean, a large SD means the scores were spread wide. The formula puts the average candidate at exactly 50, and every one SD above or below the average moves the T-Score by 10. RDSO notes that for most candidates the T-Score falls between 20 and 80, though the formula does not rule out scores outside that range.
- Your score in Test 1: 20
- Mean of Test 1: 14
- Standard deviation of Test 1: 3
- T-Score = 50 + 10 × (20 − 14) ÷ 3 = 50 + 10 × 2 = 70
Six marks above the mean, with an SD of 3, is two standard deviations above the average. That is a T-Score of 70: comfortably qualified, and well above the 60 that Pindel Sir sets as the practice target.
RDSO answers this exact complaint in its FAQ, with figures:
- Questions in the test: 100
- Mean: 85
- Standard deviation: 10
- Your raw score: 75
- T-Score = 50 + 10 × (75 − 85) ÷ 10 = 50 − 10 = 40
Seventy-five right out of a hundred looks like a strong paper. But when the average candidate got 85 right, 75 is one full SD below the average, and the T-Score is 40: not qualified. This is the trap of the speed tests. In the Power of Observation Test and the Perceptual Speed Test, most candidates score high, so the mean is high, and every careless error pushes you further below it. A score that feels good is not enough; you have to be at least near the middle of the group.
- Questions in the test: 50
- Mean: 40
- Standard deviation: 5
- Your raw score: 0
- T-Score = 50 + 10 × (0 − 40) ÷ 5 = 50 − 80 = −30
RDSO adds that such candidates are very few. The lesson is not the number but the cause: a zero in one test. It happens when the study part of the Memory Test goes wrong and the candidate gives up on the test part, or when a candidate misreads the instruction screen and answers a different question from the one asked. The CBAT has no negative marking, so there is never a reason to leave a question blank, and never a reason to stop before the clock does.
Four rules from RDSO's FAQ, in one place:
- To qualify, a T-Score of 42 or more is needed in each test of the battery.
- The cut-off is the same in all RRBs across the country, with no variation.
- There is no provision of reservation in the aptitude test, because it selects staff for safety categories.
- There is no negative marking, because the test measures attributes, not knowledge.
Put 42 on the scale: it is 0.8 of a standard deviation below the average candidate. On a normal curve about one candidate in five lands below that line in any one test. That sounds easy until you remember that you must clear the line five times in a row, in five different abilities. A good Memory Test does not rescue a weak Depth Perception Test. Each test is a separate pass or fail.
The aptitude test carries a weight of 30 in the final selection, and RDSO's FAQ shows how the five T-Scores become a score out of 30:
- Add the T-Scores of the five tests. RDSO's example: 300.
- The maximum is taken as 80 × 5 = 400.
- Score out of 30 = 300 × 30 ÷ 400 = 22.5
The scores in the RRB examination and in the aptitude test are then apportioned 70:30 for the final merit list. So 42 is a floor, not a goal. Every T-Score point above 42, in every test, adds to your composite score and lifts your rank. The Full Mock scorecard on the Kautilya Classes portal is out of 30 for this reason: it uses the same formula on the same five T-Scores, so one look tells you both whether you qualified and how much merit the five tests earned.
- Aim at 60, not 42. A target of 42 leaves no room for a hard paper, a slow start or a bad night. Sixty in every test is one SD above the average, and it is reachable with practice.
- Treat the five tests separately. Find the weakest one on your scorecard and give it the most days. The strongest test cannot carry it.
- In the speed tests, be exact first. When the mean is high, one careless error costs more than one slow answer. Build accuracy, then speed.
- Never leave a blank. No negative marking means a guess can only help. When Time Left is nearly gone, answer everything that remains.
- Practise where a T-Score is reported against other candidates. A percentage tells you nothing about the group. On the portal every paper's T-Score is computed against every student who sat that paper, with the formula above, and the Full Mock gives all five T-Scores and the score out of 30 in one scorecard.
Start with the free Full Mock: create a free account, sit the five tests in the hall's order, and read the five T-Scores. Then take the kinds of your weakest test from the list of all 20 kinds of question, and the packages when you want every practice paper.
ALP साइको टेस्ट (CBAT) का हर परिणाम T-Score में आता है, सही उत्तरों की गिनती में नहीं। RDSO का सूत्र है T = 50 + 10 × (आपका स्कोर − औसत) ÷ मानक विचलन, जहाँ औसत और मानक विचलन उस टेस्ट में बैठे सभी उम्मीदवारों के अंकों से निकलते हैं। औसत उम्मीदवार का T-Score ठीक 50 होता है। हर टेस्ट में 42 या उससे ज़्यादा T-Score ज़रूरी है, और यह कट-ऑफ पूरे देश के हर RRB में एक जैसा है; न आरक्षण है, न नेगेटिव मार्किंग। RDSO का उदाहरण याद रखें: 100 में से 75 सही होने पर भी, अगर औसत 85 और मानक विचलन 10 हो, तो T-Score सिर्फ़ 40 आता है, यानी असफल। पाँचों टेस्ट के T-Score जोड़कर, 400 से भाग देकर, 30 से गुणा करने पर 30 में से स्कोर मिलता है (जैसे 300 → 22.5), जो अंतिम मेरिट में 70:30 के अनुपात से जुड़ता है। पिंडेल सर की सलाह: लक्ष्य हर टेस्ट में 60 रखें, कोई सवाल खाली न छोड़ें, और वहीं अभ्यास करें जहाँ T-Score दूसरे उम्मीदवारों के मुकाबले दिखे।
Source: RDSO (Research Designs and Standards Organisation, Lucknow), Psychology Directorate, Candidates' Corner and Frequently Asked Questions, rdso.indianrailways.gov.in. The ALP test pattern is from the RDSO guideline "ALPs Guidelines CBT, Jan 2020".