Our obsession with normal values

Area of Science:

• Medical Imaging
• Biostatistics
• Clinical Interpretation

Background:

• Normal values are fundamental for interpreting quantitative imaging data in routine clinical practice.
• The methods for obtaining, presenting, and interpreting normal values are often overlooked.
• Accurate normal values are essential for reliable diagnostic assessments.

Purpose of the Study:

• To review the fundamental concepts of normalcy in quantitative imaging.
• To discuss the implications of typical normal ranges and data distributions.
• To explore methods for adjusting normal values for confounding factors and acknowledge their limitations.

Main Methods:

• Literature review on the concepts and statistical considerations of normal values.
• Analysis of normal data distributions and their impact on interpretation.
• Discussion of methods for indexing normal values, such as body surface area adjustments.

Main Results:

• Normal value determination involves complex statistical and biological considerations.
• Typical normal ranges can vary based on data distribution and patient factors.
• Adjusting for factors like body surface area is possible but has limitations.
• The concept of normal values has inherent limitations in addressing complex clinical problems.

Conclusions:

• Establishing and interpreting normal values requires careful attention to methodology and statistical principles.
• While adjustments for biological factors can be made, the inherent limitations of normal values persist.
• There are no simple statistical solutions for the complex clinical challenges involving normal value interpretation.