Stability Testing Protocols

Any system that can handle a great deal of stress without significantly changing its behavior is said to be stable. Stability testing is an important aspect of research and product development in many different fields, including pharmaceutical research, computer programming and academic research. The specific protocols vary a great deal, but the underlying notion of subjecting the system to adverse conditions is the same throughout.

Mathematics

• An equilibrium is stable if small perturbations do not knock the system out of equilibrium. A ball in a ditch is stable because after a small kick, it will settle down again. A ball on top of a hill is not stable because after a small kick, it will roll down the hill.

  Stability is tested by substituting the equilibrium solution with one that is slightly different and checking to see if the difference decays or increases over time. If it decays, the solution is stable. This approach is very general, and the specific details depend on the exact equation being studied. Stable equilibria are important in physics, astrophysics, economics and any other field that relies on mathematical formalism.

Software

• Applications that freeze or crash regularly are unstable. After an application has been written and debugged, it should be tested for stability. Stability in this sense is not clearly defined; the less likely a program is to crash, the more stable it is. Functions within the code are divided into primary functions, which are vital for regular use, and contributing functions, in which problems would be more of a nuisance. Primary functions should be tested thoroughly, ensuring that they do not lose data, hang or crash and that they do not interfere with the underlying operating system. Contributing functions should be checked as time allows.

Pharmaceuticals

• Pharmaceutical stability measures the amount of time a drug can safely be used after it has been produced. It is essentially the process of determining a drug's expiration date. Stability depends on the drug, how it is packaged (capsule, pill, liquid) and environmental conditions, such as temperature and moisture.

  The Food and Drug Administration says three batches are the minimum to start a long-term stability program. The conditions that the drugs are stored in should be documented, and the drugs themselves tested quarterly for the first year, semi-annually the second year, and annually after that. Drugs that are susceptible to light or moisture should be tested under these conditions unless the company has proven that its packaging prevents such degradation.