Producing reliable equivalent versions of a test using CTT is difficult since reliability estimates are only useful for the sample on which a test is trialled and cannot be extended to other samples of students of differing proficiency (Alderson et al. [1995]).
The complexity of the system structure and failure mechanism makes it more difficult for reliability assessment of these systems.
The faults caused by process variation and degradation are different, which makes it difficult to handle reliability.
It has been observed that these methods involve complex computations and it is very difficult to calculate reliability of the system by these methods.
Since IEC 61508-6 does not give detailed explanations of the definitions and PFDavg calculations for its examples, it is difficult for common reliability or safety engineers to understand when they use the standard as guidance in practice.
But statistical model for microbial community remains rarely known and therefore it is difficult to evaluate reliability of the results.
The presence of inconsistent responses may positively or negatively bias the Cronbach's alpha, making the assessment of internal reliability difficult.
Requiring probability density distribution functions of uncertain variables, it is difficult for conventional structural reliability analysis methods to calculate the reliability of composite laminates with both random and interval variables.
But there is a reassuring logic to her proposals for navigating difficult passages with greater reliability and less strain.
In many of these cases, the reported sex of the supposedly long-lived tortoise, or the species, or even both, have mysteriously changed during captivity, making it difficult to accept the reliability of such reports.
