Methods failures

Insufficient testing is one of the major causes of method failure. The amount of data needed to publish a new procedure in a peer-reviewed journal and the procedural detail supplied therein are often insufficient to allow a different user to validate a method rapidly. The developer should evaluate if the method will work using chemicals, reagents, solid-phase extraction columns, analytical columns, and equipment from various vendors. Separate lots of specific supplies within a vendor should be evaluated to determine if lot-to-lot variation significantly impacts method performance. Sufficient numbers of samples should be assayed to estimate the lifetime of the analytical column and to determine the effects of long-term use on the equipment. 

Method failure (perfect-use failure) is a failure inherent to the proper use of the contraceptive alone. 

Any method developed for widespread use over a number of years is worth a thorough ruggedness test which will reduce the chance of method failure, and thus is worth testing at three levels. 

The actual effectiveness of any contraceptive method is difficult to determine because many factors affect contraceptive failure. A failure inherent to the proper use of the contraceptive alone is considered a method failure or perfect-use failure. User failure or typical use failure takes into account the user s ability to follow directions correctly and consistently" (Table 77-1). In a survey of women having abortions in 2000-2001, 46% had not used a contraceptive method in the month they conceived owing to a perceived low risk of pregnancy (33%) and concerns about the use of contraceptives (32%). The male condom was the most commonly used method (28%), from which inconsistent use was the cited cause of pregnancy in 49% of cases. Oral... 

OC can resolve repeated monthly menstrual bleeding." However, by the fifth year of use, regular bleeding cycles may resume in more than 60% of users. Regular cyclic bleeding in a woman who is using Norplant indicates return of ovulation and a higher risk of method failure. ... 

A method breakdown can happen any time, often when least expected. In most cases, a method failure is indicated by unexpected results. However, it may also happen that method breakdown occurs gradually, and identifying such an assay failure is not trivial. Therefore, it may take several assay runs before a method failure becomes obvious. In such a case, it is important to identify method failure early on, to prevent excessive reanalysis of test samples or significant repeats of experiments that are part of method transfer or validation. 

Method failures can, of course, occur at any stage in the progression from transfer to validation to sample testing. Therefore, the troubleshooting process discussed in this chapter applies to any of these stages. 

Identification of Method Failures and Trending of Assay Performance... 

Hypotheses to explain method failures will be based on available facts. Therefore, it is of advantage to gather as much information as possible about the failed assays, as well as assays that performed well, to narrow down potential causes for the failures. Creating tables containing, for example, information on all reagents and buffers (and their lot numbers), disposables, assay conditions for each step, operators, and instruments, is a first step in identifying potential culprits. Based on the nature... 

If pneumatic pressure testing is to be done, all radiographable welds are examined completely by this method and all others by the magnetic particle or liquid penetrant method. Failure during a pneumatic pressure test simply cannot be permitted. 

Occasional method failure can occur before or after chemical separation. A variable fraction of the radionuclide may be lost during storage or initial treatment before the carrier or tracer is added, or interchange between the carrier or tracer and the radionuclide of interest may be incomplete. During counting, instrumental effects such as quenching may be inaccurately assessed. 

Sparrow MJ. Pill method failures. NZMedJ l987) 100, 102-5. 

ASTM D256 Standard Test Methods for Determining the Izod Pendulum Impact Resistance of Plastics. Used to determine the resistance of a plastic specimen to impact by a pendulum-type hammer. Specimens contain a milled notch and depending upon the test method, failure may be brittle or ductile. Test results are reported in terms of energy absorbed per unit of specimen width or per unit of cross-sectional area under the notch. 

The reason for any Hartree-Fock method failure can be only one thing the wave function is approximated as a single determinant. All possible catastrophes come from this, and we might even deduce when tiie Hartree-Fock method is not appropriate for description of a particular real system. First, let us ask when a single determinant would be OK Well, out of all Slater determinants tiiat could be constructed from a certain spinorbital basis set, only its energy (i.e., the mean value of tiie Hamiltonian for this determinant) would be close to the true eneigy of... 

An inspection by Daimler-Benz of elastomer components for use in car construction showed that the percentage of defective components was much higher than that for plastics or metal parts. Reasons for this situation are discussed and ways and methods (failure mode effects analysis and statistical process control) of improving the quality of rubber injection mouldings outlined. It is concluded that quality should be achieved by quality planning and development rather than by quality control. 13 refs. 

From experimental results, it has been observed that the fiber-matrix interface might fail catastrophically. This failure mode can be attributed to the stress concentration at the fiber and matrix junction, and at this point, failure initiates and rapidly propagates along the interface. Another approach for fiber-matrix interface failure is based on energy methods. Failure may occur if the interface fractures with work of fracture (Gi) per unit area of interface. The source of the required fracture surface energy is the strain energy stored within the specimen components [42-44,47]. 

RAPP method Failure analysis and risk determination in automobile fleets within the case study electric actuator... 

Design choices frequently determine construction methods failure to recognise this and force the process in the opposite direction leads to muddle and make-do. 

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