Reference Interval Calculator
Enter a set of measurements to automatically compute descriptive statistics, the Shapiro-Wilk normality test, and both a parametric (mean ± 1.96 SD) and a non-parametric (P2.5–P97.5 percentile) 95% reference interval, with the appropriate method recommended per CLSI EP28-A3. Suitable for establishing normal reference ranges for brain ADC by gestational week and other quantitative indicators.
① Enter data
Paste or enter a set of values, separated by spaces, commas or line breaks. You can paste a single column directly from Excel.
How to use & methodology
What is a reference interval and when is it built?
A reference interval is the range covering 95% of a healthy population for a measurement (usually P2.5–P97.5), used to judge whether an individual value is within the normal range. It is needed when establishing normal ranges for fetal brain ADC by gestational week and other quantitative indicators.
Why test normality first?
The method depends on the distribution. If the data are normal, the parametric method (mean ± 1.96 SD) can be used; if not, the non-parametric method (P2.5 and P97.5 percentiles) should be used. This tool auto-determines the distribution with Shapiro-Wilk and recommends accordingly.
How large a sample is needed?
CLSI EP28-A3 recommends at least 120 subjects for a non-parametric 95% reference interval; if partitioning (e.g. by sex or gestational-week band), about 120 per partition. The parametric method can use somewhat fewer with normal data, but at least ~40 per group is still advised.
How do I prepare the data?
Paste or enter a set of measurements; spaces, commas and line breaks are all supported, and you can paste a single Excel column directly. The tool outputs descriptive statistics, the normality test, and both parametric and non-parametric reference intervals for comparison.