Drybench Assay.
Z prime factor calculator
Z′ from your positive and negative control wells with sample standard deviations and n shown, compared with the 0.5 convention as an observation.
Z′ describes how far apart this plate's controls sit relative to their spread. It is one observation about the controls, not a pass or fail, and not a condition for fitting or reporting a curve: in this app, whether a midpoint is reported is decided by the reporting rules stated in each result, among them the within-plate permutation test.
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Answer
Z′
0.782Z′ (Zhang, Chung and Oldenburg 1999)
means 1.242 and 0.06; sample SDs 0.0722 and 0.0136 (n − 1); n = 8 and 4
At or above the 0.5 convention of Zhang, Chung and Oldenburg 1999, read as an observation.
Preloaded: the worked MTT plate's eight vehicle wells and four kill-control wells.
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The 0.5 convention is Zhang, Chung and Oldenburg's (1999) and is shown beside the value for reference.
What this page does not do
Judge an assay, a plate or a screen; compute SSMD, a sample-based Z or signal-to-background; gate any curve.
Worked example
- The worked MTT plate: eight vehicle wells (mean 1.242) against four kill-control wells (mean 0.060) give Z′ = 0.782 with sample standard deviations.
- Z′ = 1 − 3(σpos + σneg)/|μpos − μneg| with sample standard deviations (n − 1); fewer than two wells in a control, or coinciding means, give no Z′, and the published fixture includes those cases.
Method
- Z′ (Zhang, Chung and Oldenburg 1999). Zhang J-H, Chung TDY, Oldenburg KR. A simple statistical parameter for use in evaluation and validation of high throughput screening assays. J Biomol Screen 1999;4:67-73 (read 5 October 2026); sample SD (n − 1), n shown.Checked against Z′ worked by hand with sample standard deviations on 5 control sets, including the MTT plate and a set refused for a one-well control, within 1e-9 (2026-10-06); and on 6 degenerate and adverse sets (one well in either control, coinciding means, no spread, a negative Z′) in R, within 1e-9 with the refusals exact (10 October 2026).
Limits
- For research and education only, and not medical advice: a C50 estimated here describes this assay under these conditions and is not a binding constant.
- Normalisation uses each plate's own control means, and Z′ uses sample standard deviations: Z′ below 0.5 is an observation against Zhang's convention, not a pass mark, and R² is shown but is not a goodness-of-fit gate.