How would you define acceptance criteria for a validation protocol?

Why

Start from the intended product quality and the critical attributes that the process must maintain, then connect process variables and controls to those outcomes. A mixing validation could assess homogeneity across tank locations, operating speed and hold times using a qualified analytical method. Define sample locations, test methods, limits, statistical treatment and conditions that constitute a protocol deviation before collecting data.

Regulatory specifications may set some limits, but additional capability criteria can be appropriate to demonstrate a robust process. Include meaningful high-risk operating ranges and measurement uncertainty. Acceptance must not be revised after seeing failures just to secure a pass.

A protocol may require investigation and scientific justification if unexpected results arise, even when every final batch release assay appears compliant.