Percentile Explorer

Explore the distribution of left ventricular mass across different scaling methods and references.

Understanding Percentiles & Reference Ranges

Interactively explore how percentiles relate to z-scores and confidence intervals on a normal distribution.

Percentile: 95%
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Percentile Interpretation:

z-score: 1.65

95% of values are below 1.65 SD

5.0% of values are above 1.65 SD

Formula: Mean + 1.65 × SD

Confidence Interval:

z-score: ±1.65

90.0% of values are within ±1.65 SD

(95% - 5.0% = 90.0% symmetric around mean)

Formula: Mean ± 1.65 × SD

Calculating the Upper Limit of Normal (ULN):

At the 95th percentile (z=1.65), the formula is: ULN = Mean + 1.65 × SD

-4-3-2-101234Standard Deviations from Mean (Z-score)Probability DensityMean95th %ilez = 1.655.0th %ilez = -1.65

Key Points for LV Mass Scaling:

  • 95th Percentile (z = 1.65): This is commonly used as the upper limit of normal (ULN) in echocardiographic reference values. It means that 95% of the normal population falls below this value.
  • Mean + 1.65 × SD: This formula gives you the 95th percentile value, assuming a normal distribution.
  • Mean + 2 × SD: This is approximately the 97.7th percentile, which is more relaxed than the 95th percentile threshold.
  • 95% Confidence Interval (Mean ± 1.96 × SD): This is different from the 95th percentile. It represents the range where 95% of values fall (from the 2.5th to the 97.5th percentile).

Application to LV Mass Normalization:

When studies provide mean and SD values rather than explicit percentiles, using mean + 1.65 × SD gives the appropriate 95th percentile threshold for identifying left ventricular hypertrophy.