At the bottom of each daylily cultivar's database page there is a link (called "Read our note about daylily rust scores") that explains how daylily rust scores were derived from averaging the scores collected over the years by university scientists who were funded and supported by AHS in their research on daylily rust. Citations are provided to the data and research used in those averaged scores.
Since the decimal scores (1, 1.1, etc) are averages arrived from scientific data over a number of controlled observations, any individual's change to the rating would only reflect rust in their own "back yard" so to speak. Depending on how a lay-person interprets their experience, a plant's condition, and how scores should be defined, changing the decimal number would likely skew the research data to the point of being useless (that is, its an averaged result of years of research, not a running tab of any individuals).
Here's the explanation listed in the link at the bottom of every daylily cultivar's page, as mentioned above:
Scientifically cited, succinct, and easiest-to-read explanation and sub-links (as well as the source for the links to much of the published research below): Sue Bergeron's site (2011-2012 AHS member of Committees on Educational Outreach and Scientific Studies)
http://web.ncf.ca/ah748/rust.h...
2) What is being seen in the decimal-number ratings:
A meta-analysis rating of an average score obtained across all scores for the cultivars studied in the noted research. In other words, an average of the already-averaged scores from all the sources.
3) What these general numbers mean, as borrowed from the research reports from the sources listed further below:
1 - No visible signs of rust (termed 'shows resistance' and 'shows vertical resistance' in scientific literature)
2 - Slight amount of visible rust, determined by percentage of foliage covered in rust pustules (termed 'shows resistance' and 'shows horizontal resistance' in scientific literature)
3 - Moderate amount of visible rust, determined by percentage of foliage covered in rust pustules (termed 'shows susceptibility' in scientific literature)
4 - Heavy amount of visible rust, determined by percentage of foliage covered in rust pustules (termed 'shows susceptibility' in scientific literature)
5 - Complete rust infestation, determined by percentage of foliage covered in rust pustules (termed 'shows susceptibility' in scientific literature)
4) Where the data comes from (published databases and scientific literature sources):
2012 University of Georgia and Ibaraki University (Japan), James W. Buck (Ph.D., Plant Pathology, Univ. Wisconsin-Madison), Yoshitaka Ono (Ph.D., Agricultural Science, Purdue University).
2007 USDA Report, Y. H. Li (Ph.D., Plant Pathology, University of Arkansas) , M. T. Windham (Ph.D., Plant Pathology, North Carolina State University), and R. N. Trigiano (PhD., Plant Pathology and Botany, North Carolina State University), D. C. Fare (Ph.D.,Agronomy and Soils, Auburn University), United States Department of Agriculture.
2005 University of Arkansas, Rust Obersvations, Allen Owings (Ph.D., Horticulture, Mississippi State University), Gordon Holcomb (Ph.D., University of Wisconsin, Madison).
Circa 2003: from links page:
http://web.ncf.ca/ah748/rust.h... - Congregate observations (correlated with university field observation research data) in four performance categories converted to university researcher's 5.0 scale using weighted averages.
2002 University of Georgia, Department of Plant Pathology, Daren S. Mueller (Ph.D, Plant Pathology at University of Illinois at Urbana-Champaign), Jean L. Williams-Woodward (Ph.D., Plant Pathology, University of Minnesota), James W. Buck, Department of Plant Pathology (Ph.D. Plant Pathology, Univ. Wisconsin-Madison).
2002 Rust Score Report, Cornell University, Karen Snover-Clift (M.S. Plant Pathology, Cornell University), Director of the Cornell University Plant Disease Diagnostic Clinic of the Department of Plant Pathology.
2001 Field Research, University of Arkansas, James A. Robbins (Ph.D., Environmental Horticulture, University of California, Davis) and Steve Vann (Ph.D., Plant Pathology, Texas A & M).
