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BA II Plus: Standard Deviation Step by Step
Use the BA II Plus DATA and STAT worksheets to compute sample standard deviation.
TL;DR
The DATA worksheet stores observations and the STAT worksheet reports mean and standard deviation. CFA questions often require sample standard deviation unless the population is explicitly provided.
Formula Reference
Sample standard deviation
s = sqrt[sum(x_i - mean)^2 / (n - 1)]Use sample standard deviation for a sample of observations.
BA II Plus Keystrokes
- 2nd DATA
- 2nd CLR WORK
- Enter each X value and press ENTER
- Use down-arrow to move to the next X value
- Press 2nd STAT
- Scroll to Sx for sample standard deviation
Worked Example
- Problem: Returns are 4, 7, and 10 percent.
- Enter 4, 7, and 10 in DATA.
- STAT reports mean = 7 and Sx = 3.
Common Mistakes
- Reading sigma x when the question asks for sample standard deviation.
- Leaving old data in the DATA worksheet.
- Entering percentages inconsistently.
Related Guides
- CFA Level I Quantitative Methods Calculation Guide - Formulas, examples, and calculator workflows for CFA Level I quantitative methods.
- CFA Level I Quantitative Methods Formula Sheet - Public formula sheet for CFA Level I quantitative methods calculations.
- BA II Plus: Mean and Variance Step by Step - Calculate mean and variance from a data set using BA II Plus statistics outputs.