In the failure rate calculation, acceleration factors (AFij) are used to derate the failure rate from the thermally accelerated life test conditions to a failure rate indicative of actual use tempera- ture.
Full Answer
How do you calculate the failure rate?
The failure rate can be defined as the following: The total number of failures within an item population, divided by the total time expended by that population, during a particular measurement interval under stated conditions. (MacDiarmid, et al.)
What is a decreasing failure rate?
A decreasing failure rate (DFR) describes a phenomenon where the probability of an event in a fixed time interval in the future decreases over time. A decreasing failure rate can describe a period of "infant mortality" where earlier failures are eliminated or corrected and corresponds to the situation where λ ( t) is a decreasing function .
What is the most common unit for failure rate?
Units Failure rates can be expressed using any measure of time, but hours is the most common unit in practice. Other units, such as miles, revolutions, etc., can also be used in place of "time" units.
What is the failure rate of a device?
Failure rates are often expressed in engineering notation as failures per million, or 10 −6, especially for individual components, since their failure rates are often very low. The Failures In Time ( FIT) rate of a device is the number of failures that can be expected in one billion (10 9) device-hours of operation.
What are treatment failures?
Treatment failure is defined as persistent symptoms or signs or a sustained four-fold increase or failure to achieve a four-fold decrease in those with high-titer initial results (equivalent to a two-dilution change) in nontreponemal test titer.
What is ARV treatment failure?
Treatment failure is defined as repeated HIV RNA values above the lower limit of detection of a sensitive assay (usually 50 copies per mL). This is based on evidence that the maximum clinical benefit of antiretroviral therapy is derived by keeping the viral load as low as possible.
What is the virologic criteria for treatment failure on antiretroviral treatment?
Virological failure is defined as when antiretroviral therapy (ART) fails to suppress viral replication to lower than 1000 copies/mL, while immunological failure is a fall of CD4 + count below 250 cells/µL following clinical failure, or persistent CD4 + count below 100 cells/μL [7].
What is the meaning of virologic failure?
Virologic failure occurs when antiretroviral therapy (ART) fails to suppress and sustain a person's viral load to less than 200 copies/mL. Factors that can contribute to virologic failure include drug resistance, drug toxicity, and poor adherence to ART.
What causes treatment failure?
Inadequate interaction was the main cause of treatment failure, followed by failing primary care, secondary care and the patient him/her self; the relative responsibilities for treatment failure were 35%, 28%, 27% and 10% respectively.
What is clinical failure?
Clinical failure is the occurrence of new or recurrent WHO stage IV condition 6 months after ART initiation.
What does virological mean?
(vī-rŏl′ə-jē) n. The study of viruses and viral diseases.
What is virological test?
Virological testing. HIV infection in infants is diagnosed by detecting the presence of viral nucleic acid (i.e. viral RNA or viral DNA) often called nucleic acid testing (NAT), or viral products such as p24 Ag.
What is the difference between virological failure and immunological failure?
Virological failure was associated with non-adherence to medications, aged < 40 years old, having CD4+ T-cells count < 250 cells/μL and male gender. Similarly, immunological failure was associated with non-adherence, tuberculosis co-infection and Human immunodeficiency virus RNA ≥1000 copies/mL.
What is viral suppression?
This is called viral suppression—defined as having less than 200 copies of HIV per milliliter of blood. HIV medicine can even make the viral load so low that a test can't detect it. This is called an undetectable viral load.
What is a medical virologist?
The Role Of A Medical Microbiologist Or Virologist Medical microbiologists and virologists direct the prevention, diagnosis and treatment of infectious diseases, with viral infections being the focus of medical virologists' work. Medical microbiology and virology are pathology specialties.
Loren Stewart, CFSE
The Greek symbol lambda, λ, represents failure rates in functional safety, usually expressed in the unit of measurement of FITS.
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What is failure rate?
Failure rate is the frequency with which an engineered system or component fails, expressed in failures per unit of time. It is usually denoted by the Greek letter λ (lambda) and is often used in reliability engineering .
How does failure rate vary?
The failure rate of a system usually depends on time, with the rate varying over the life cycle of the system. For example, an automobile's failure rate in its fifth year of service may be many times greater than its failure rate during its first year of service.
Why is it incorrect to extrapolate MTBF?
Because of this, it is incorrect to extrapolate MTBF to give an estimate of the service lifetime of a component , which will typically be much less than suggested by the MTBF due to the much higher failure rates in the "end-of-life wearout" part of the "bathtub curve".
What unit is used to measure failure rate?
Failure rates can be expressed using any measure of time, but hours is the most common unit in practice. Other units, such as miles, revolutions, etc., can also be used in place of "time" units.
What is a decreasing failure rate?
A decreasing failure rate (DFR) describes a phenomenon where the probability of an event in a fixed time interval in the future decreases over time. A decreasing failure rate can describe a period of "infant mortality" where earlier failures are eliminated or corrected and corresponds to the situation where λ ( t) is a decreasing function .
What is the primary failure mechanism causing mechanical and electromechanical devices to wear out?
Mechanical movement is the predominant failure mechanism causing mechanical and electromechanical devices to wear out. For many devices, the wear-out failure point is measured by the number of cycles performed before the device fails, and can be discovered by cycle testing.
What is failure rate analysis?
From field failure rate reports, statistical analysis techniques can be used to estimate failure rates. For accurate failure rates the analyst must have a good understanding of equipment operation, procedures for data collection, the key environmental variables impacting failure rates, how the equipment is used at the system level, and how the failure data will be used by system designers.
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I supported reliability calculations for an aerospace company for years. It was common practice to assume three failures utnil enough data had been generated to produce actual failures. This approach is reviewed in Winkler, Smith, and Fryback, The Role of Informative Priors in Zero-Numerator Problems: Being Conservative versus Being Candid.
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