The terms OOS, OOE and OOT are very important from the pharmaceutical Quality Assurance & Regulatory Affairs point of view and always emerge in connection with the handling of deviating analysis results.

Out-of-Specification (OOS) results: A result that falls outside established acceptance criteria which have been established in official compendia and/or by company documentation.

Out-of-Expectation (OOE) Results: An atypical, aberrant or anomalous result within a series of results obtained over a short period of time is an OOE result. An OOE result is a result that meets specifications, but is outside the expected variability of the analytical procedure.

Out-of-Trend (OOT) Results: A time dependent result which falls outside a prediction interval or fails a statistical process control criterion. A result that does not follow the expected trend, either in comparison with other stability batches or with respect to previous results collected during a stability study.

A trend is a sequence of temporal procedures, e.g. for the manufacture of different batches of a product. There are two types of trends: In one case, no trend is expected, e.g. in production or when analyzing process data where everyone expects that they are under statistical control.

In the other case, a trend is expected. One typical example for that is stability testing where one expects that the content of the API reduces over the storage period, or that the quantity of impurities increases over time.

There is a fundamental difference between these two types of OOT results: indeed, in the second situation the dispersion increases over time.