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Photograph of no mold spores, one mite fecal.Definition of Type 1 Errors & Type 2 Errors
Effects of Type I or Type II Errors on Mold or Environmental Testing

  • POST a QUESTION or COMMENT about how to report the density or level of mold or other particles found on indoor surfaces or in indoor dust samples

Definition & examples of Type 1 & Type 2 errors:

Classes of testing or statistical errors applied to mold or other environmental tests, inspections & reports can be divided into two basic mistakes or error types as we explain here. We include the definitions of type 1 and type 2 errors and we give examples of type 1 and 2 errors in building inspection and testing for mold contamination.

It is important to understand these types of environmental testing mistakes in order to reduce unnecessary risks to building occupants (failing to detect and report an environmental hazard) as well as to avoid wasting people's time and money focusing on on-problems (reporting as hazards conditions that are in fact not hazardous).

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Definition & Practical Examples of Type I and Type II Errors in Building Environmental Testing for Mold or Other Contaminants

Photograph of Aspergillus niger spores.

Types of Reporting Errors in Buildings: definitions of Type 1 Errors & Type 2 Errors

Using building environmental testing for mold contamination as an example this article describes the types of errors that may be made by thinking, technical, or procedural errors during an investigation or test.

Type One Errors - missing a problem that's present: Occasional occurrences of certain mold genera in samples might suggest a hidden or un-noticed mold problem in the building somewhere other than at the spot from which the sample was collected.

This is particularly true if the sample was collected by someone who is not expert at building science, indoor air quality, mycology, and related disciplines.

Examples of Type I errors during a mold investigation include:

Type II Errors - asserting that a problem is present when it is not: Conversely, occasional occurrences of certain mold in samples might also seem to point a problem in a building where in fact none is present.

Photograph: typical cosmetic bluestain mold on new framing lumber, floor joists - © Daniel Friedman

This is a greater risk where mold "counts" are used in air sampling than it it is when surface sampling is combined with visual inspection. Occupant indoor air or environment-related complaints or a building history of leaks can suggest that additional investigation is in order.

Examples of Type II errors during a building mold investigation include:

See MOLD / ENVIRONMENTAL EXPERT, HIRE ? for help in determining when the risk indicators justify the cost and trouble of hiring a mold or environmental expert

To avoid both Type I and Type II errors in measuring toxic or allergenic mold exposure 

the building consultant needs to understand mycology (e.g. what mold is likely to grow in buildings), the significance of the particles found (e.g. Pen/Asp spore chains vs. individual spores), the history, construction, and materials in the building and the details of the inspection itself when interpreting the importance of low levels of mold in building samples.

The articles recommended at the end of this page provide more examples of sources of Type 1 or Type 2 errors during building mold or environmental inspection, testing, lab sample analysis, & reporting.

Avoid This Building, Mechanical System Or Indoor Environment Troubleshooting Mistake

When making an observation, be sure that we are seeing what's really there, not what we want to see or what we failed to see, that is, seeing a pattern that isn't there or failing to see a pattern that is there.

In discussing studies of bird behavior, Joan E. Strassmann notes:

Snell-Rood and Cristol made sure to conduct this experiment blind, meaning that they did not know which birds had been held in captivity and which had not.

Not knowing which bird was in which group when taking down observations is important in just about any scientific study to avoid the danger of inadvertently seeing a pattern rather than seeing what is really there.

- Strassmann, Joan E., Slow Birding, the Art and Science of Enjoying the Birds in Your Own Backyard, TarcherPerigee (October 25, 2022) ISBN-10 ‏ : ‎ 0593329929 / ISBN-13 ‏ : ‎ 978-0593329924


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Continue reading at MOLD TESTING & SAMPLING MISTAKES for more examples of how mold testing goes wrong, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

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ENVIRONMENTAL TEST ERROR TYPES at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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INDEX to RELATED ARTICLES: ARTICLE INDEX to BUILDING ENVIRONMENT

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