This application calibrates response curves against data from an immunoassay that records the concentration of melatonin in human urine and its optical density.

Melatonin is excreted by the pineal gland and regulates human circadian rhythms. Deviations outside of normal boundaries may indicate sleep disorders, depression, schizophrenia, or a range of other conditions.

Immunoassays typically generate sigmoidal response curves, with upper and lower asymptotes near the infinite and zero analyte concentrations.

This is accurately described by a four parameter logistic (4-PL) equation. A five parameter logistic equation enables the fitting of asymmetric concentration-response data.