Unlike the parallel-line assay, the expected response is linear in the dose, not its logarithm. The graphs of the response against dose for test and standard samples will be straight lines of different slopes and common intercept, as the assumptions of the assay demand the same outcome for standard and test samples when the dose is zero. The analysis can be accomplished by a multiple regression, with the estimator of *p* being the ratio of the slope estimators. Interval estimates are often obtained using Fieller's theorem.

You can see a sample graph on the left. With PLA 3.0, you are able to calculate slope-ratio assays for each standard/test sample combination in your bioassay seperately or simultaneuosly.