Percentile estimate with respect to a positive reference serum

Percentile estimate with respect to a positive reference serum Non-parametric methods are preferable for the estimation 

A cumulative frequency distribution is prepared from the absorbance values of sera from a large normal group ( 100). This standard curve serves then as reference to establish the percentiles or P-values (de Savigny et al., 1979). Above a certain absorbance value the test sample is reported as 100th percentile or P 1.0. The reference group must be carefully selected and defined which may pose several problems. Moreover, the percentile method requires the initial testing 

Procedures to improve precision of curve fitting for antigen dose-response curves 

Absorbances observed and absorbances calculated after curve-fitting  

The general form of the four-parameter logistic function is  

---