I seldom provide comments on the forum because I prefer to read and learn.
Here, I wish to inform the community:

The content in ANSI/AARST standards are not controlled by any single interest group, government or private party. While there is desire to always have a wide spectrum of stakeholder viewpoints including several government folks representing their stakeholder vantage point, no interest group is allowed to represent more than 1/3rd of voting participants.

Overwhelming consensus for almost two decades by radon industry participants and others has supported needs for training where public demonstration of adequate training comes with passing certification exams and maintaining certification.

For the committee that approved this proposed update to MAH 2014 being referred to, folks that represent government interests are 4 out of 27 discussion participants and 3 out of 16 different voting stakeholder groups.

The consensus summary is not too hard to understand: The job of a testing professional entails far more than plugging in, unplugging and hitting print buttons on a test device.

Warmest regards to all,
Gary Hodgden
Secretariat for the ANSI/AARST Consortium on National Radon Standards

Dick,
Just some informational bantering on it.... It's not really so complicated as many studies imply.

A building is a living and breathing animal that comes in wide variety of species. The anatomy of the these animals (boxes) are extremely rudimentary compared to the human anatomy. They breathe air in and out. But their primary purpose and requirement is human comfort.
These animals are simple enough that one can be confident that for every action, there will be a reciprocal reaction that is definable. For instance: If you suck air out of a box (building), the volume of air being expelled will come from somewhere. And it will come from somewhere that is usually quite predictable. For our purpose and example, we can confidently predict that indoor radon concentrations are significantly influenced only by pressure changes (that increase or decrease the volume of radon entry) or dilution after radon entry.

Studies are designed to look at a specific phenomena but the scope of most studies does not include getting definitive on why the phenomena witnessed is occurring. For instance, I recall reading a study that was commissioned by a manufacturer to prove whether or not this one gadget (product) that pulls a lot of air out of the basement would consistently lower radon readings and humidity. The study concluded success. But it did not elaborate on why. In this case, it would not be in the interest of the manufacturer to describe the energy penalties from massive increases in air exchange rates for the building.

It seems here (as an analogy): If we evaluate blood pumping relative to breathing functions for a large number and a wide range of mammal species, we will have very interesting data that is useful in some way. But whatever the data suggests, its conclusions are too broad-brushed for use in medical applications for a human body (i.e., specific species). Our building animals are rudimentary boxes by comparison, but the challenge? They come in a wide variety of species. I have yet to see a study conducted that segregates the more than a dozen similarly configured and common building styles (species) that exist out there.
2 cents of banter.
Gary

I think there a few important distinctions to make whenever discussing these topics:

1) Can passive efforts reduce radon? The short answer is yes (with the caveat of sometimes, maybe and it depends);
2) Do passive efforts achieve safe levels (i.e., below the action level)? The short answer is not very often;
3) Can study data that averages effects of weatherization and passive efforts across various populations of homes be used for making decisions about the building(s) you are working on? No. This is because the ramifications from weatherization and passive efforts are both "sometimes, maybe and it depends."

To elaborate:

My item 1 and 2: From 1988-1994, "phased in" mitigation ruled. My stats on a few thousand homes indicated (when weather was similar both before and after the work) a rough average of 20% reductions from sealing efforts with an occasional > 50% reduction and ..... every so often an actual increase rather than reduction of indoor concentrations. So while we gain a health benefit with as little as 10-20% reduction, fat chance for reducing 8 pCi/L to > 4 pCi/L with passive efforts.

My item 3: A study in the early 1990s indicated virtually the same reductions from sealing the attic (to close air escape routes) as achieved by closing entry points at the slabs. Almost all such studies on passive efforts (e.g., sealing of slabs, attics and passive RRNC piping) have traditionally reported "as much as 50% reductions."

It's really pretty simple for radon as it would apply to smells or CO from combustion appliances: If too potent for natural ventilation to handle, the pollutant requires powered-venting (e.g., for radon, this means ASD or dilution).

The study is an admirable effort that reconfirms a lot of published data. The interpretations of the data are however less than comprehensive.
For instance: If weatherization reduces air-change-rate ventilation, do radon concentrations increase? The short answer is yes. However (like the mobile home is these studies that would be inherently leaky): if weatherization also reduces the amount of air that escapes the upper portion or topside of the building, stack effect has been impacted to reduce the flow (volume of radon entry) and the degree of negative indoor pressure (in terms of negative indoor air pressure compared to the air pressure under the building).
As these realities play out across a wide sampling of different structures and their customized extent of weatherization, it is no surprise that conclusions indicate a random relationship.

If I were asked about optimizing weatherization, I would say invert the current focus: seal air escape routes first rather than cold air entry-routes; continue sealing downward for any large openings; but also limit airtight sealing in lower lived-in areas to the extent that a desired air-change-rate for the building is still maintained for reducing airborne hazards from biological and chemical concerns.
2 cents