Normalisation – Simple Example
RRB Methodology: Percentile + Base Shift + Interpolation ✅
Railway Board authorised RRB Ajmer to adopt the normalisation methodology followed by Railway Recruitment Boards for Computer Based Tests conducted in multiple shifts. As per the RRB method, Percentile Score is used for merit, and Normalized Marks are calculated through Base Shift / interpolation.
Example
Exam held in 2 shifts:
Shift 1 – Tough Paper
3 candidates appeared.
Shift 2 – Easy Paper
4 candidates appeared.
Maximum marks: 100
Step 1: Raw Marks
Since Shift 2 has a higher average ( because of easy paper), Shift 2 is taken as Base Shift in this example.
Step 2: Percentile Calculation
Formula: Percentile = Candidates scoring equal or below ÷ Total candidates in that shift × 100
Percentile in Tough Shift
Percentile in Easy Shift / Base Shift
Step 3: Normalized Marks
Since Easy Shift is Base Shift, its raw marks become reference marks.
Now Tough Shift candidates are mapped to Base Shift.
T1
T1 percentile = 100.00000
Base Shift 100 percentile marks = 95
So, T1 Normalized Marks = 95
T2 – Interpolation
T2 percentile = 66.66667
In Base Shift:
75 percentile = 85 marks
50 percentile = 75 marks
66.66667 lies between 75 and 50.
Difference between marks = 85 − 75 = 10
Difference between percentile = 75 − 50 = 25
T2 position above 50 percentile = 66.66667 − 50 = 16.66667
Marks increase = 10 ÷ 25 × 16.66667 = 6.66667
T2 Normalized Marks = 75 + 6.66667 = 81.66667
T3 – Interpolation
T3 percentile = 33.33333
In Base Shift:
50 percentile = 75 marks
25 percentile = 65 marks
33.33333 lies between 50 and 25.
Difference between marks = 75 − 65 = 10
Difference between percentile = 50 − 25 = 25
T3 position above 25 percentile = 33.33333 − 25 = 8.33333
Marks increase = 10 ÷ 25 × 8.33333 = 3.33333
T3 Normalized Marks = 65 + 3.33333 = 68.33333
Final Normalised Position
Final Merit
Merit is based on Percentile Score. If the Percentile Score is the same, tie is decided by age first, and then by alphabetical order.
Simple Understanding
T1 got only 80 marks in tough paper.
E1 got 95 marks in easy paper.
But both are toppers in their own shifts. So:
T1 = 100 percentile
E1 = 100 percentile
After normalization also:
T1 = 95 normalized marks
E1 = 95 normalized marks
Therefore, normalisation protects candidates who faced a tougher paper.
Key Points for Aspirants
Percentile is not the percentage of marks.
Percentile shows your position in your own shift.
The topper of each shift gets 100 percentile.
Base Shift is selected for calculating Normalized Marks.
If an exact percentile is not available in Base Shift, interpolation is applied.
Final merit is based on Percentile Score.
Same percentile means tie; rank depends on age and then alphabetical order.
Disclaimer
This normalisation example has been prepared with the assistance of ChatGPT, after taking due care to align it with the RRB normalisation methodology, including Percentile Score, Base Shift and interpolation principles.
It is intended only for simple academic understanding of aspirants. Actual normalisation, calculation, rounding, tie-breaking and merit preparation will be done strictly by the Railway Recruitment Board / competent authority as per official rules, data and software-based processing.
Aspirants are advised to refer to the official Railway Board / RRB instructions for final and authoritative guidance.
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