For an approachable summary and examples of how Intactness is calculated, please see our "ABMI Essentials" two-pager on the subject HERE, or read on below for a brief overview.  

The species intactness index compares the predicted relative abundance of each species across the reporting region to the predicted abundance for that species if there were zero human footprint in the same region. This measure of intactness is scaled between 0 and 100, with 100 representing current abundance equal to that expected under reference conditions (i.e. no human footprint), and 0 representing species abundance as far from the reference condition as possible. Deviations from intact conditions occur when species become more abundant or less abundant than expected due to habitat modifications. Thus, a species that is less abundant under current conditions than under reference conditions will have an intactness value of less than 100. Likewise, a species that is more abundant under current conditions than under reference conditions will also have an intactness value of less than 100. The direction (positive or negative) of any difference between the current and reference abundances for a species is unimportant; only the degree. By extension, the greater the deviation from 100% intact, the larger the impact of human footprint (e.g. agriculture, urban development, roads) on a given species’ abundance.

*Note: Maps shown are the color blind versions of the maps.

Intactness is first calculated at the species level, then averaged across groups. For example, if the ABMI reports the intactness of old-forest birds, the values of all species in this group are averaged. Similarly, intactness for a taxon is the average of all species in that taxon.

To calculate overall intactness of all organisms the ABMI surveys (birds, vascular plants, mites, bryophytes, lichens, and mammals), species within each taxon are averaged first, and the taxa are then averaged for a final intactness value. This way each taxon is weighted equally, regardless of how many species it contains.

See a more detailed description of the analyses and limitations in the intactness manual.