The phrase "are difficult to standardize" is correct and usable in written English.
You can use it when discussing processes, measurements, or practices that lack uniformity or consistency, making them hard to establish a standard for.
Example: "The various methods of data collection are difficult to standardize, leading to inconsistencies in the results."
Alternatives: "hard to standardize" or "challenging to standardize".
What types of objects are difficult to standardize (such as the length of French fries and ingredients in a recipe)?
Background: Pharmacologic studies in atopic eczema (AE) are difficult to standardize.
Although they can test problem solving skills in real work situations, they are difficult to standardize (Kane 1992).
Although regulatory authorities recommend cell-based assays for detection of neutralizing antibodies (NAbs), such assays are difficult to standardize, and ill adapted to high-throughput analysis.
From the diagnosis standpoint, both, functional (clotting) or immunological assays, are difficult to standardize and to optimize, due to the absence of reference material, or a characteristic clinical group, and international reference preparations.
Application techniques are difficult to standardize and there may be significant intraoperator differences.
However, 3D analysis based on NHP as a reference plane is still controversial because of its sensitive reproducibility technologically and it is difficult to standardize [18].
Their isolation usually involves density fractionation of mononuclear cells (MNC) but this is difficult to standardize, especially under good manufacturing practice (GMP) conditions.
Objective measurement of deformity and its correction are often quoted but overall outcome is difficult to standardize between papers as some authors use their own version of the 'excellent, good, fair, poor' system.
These factors must be considered although it is difficult to standardize all of these factors as they are not controlled and differ from person to person due to natural differences among people and lifestyles.
