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Guest Editorial

Rio Scale: Imperfect But Not Meaningless
by H. Paul Shuch
Executive Dierector Emeritus

Our friend and colleague John Traphagan favored us with a recent guest editorial titled "SETI and the Meaningless Rio Scale" (SearchLites Vol 23 No 4, Autumn 2017, pp. 4-5). I find much with which to agree in John's analysis of the Rio Sale, an analytical tool developed nearly two decades ago to quantify the significance of purported SETI detections. I respectfully take issue, however, with his title. Just because a tool has room for improvement doesn't necessarily mean that it has no value. Allow me to respond to some of John's specific criticisms.

(1) The Rio Scale is subjective.

Absolutely true. If you ask two SETI scientists to assign a Rio value to a given observation, they will give you three different solutions. SETI is a highly interdisciplinary endeavor. Its practitioners are diverse in training, skill sets, and specialization. The subjective nature of detection analysis is a healthy thing. It triggers discussion (and sometimes lively debate) within the SETI community, from which a consensus generally emerges.

(2) The Rio Scale is speculative.

Absolutely true. That is the nature of SETI science. Until an intelligent extraterrestrial walks up to me, extends its tentacle, shakes my hand, and says "take me to your leader," anything I say about its existence is mere speculation. None of us speaks in absolutes, until solid evidence is available for all to evaluate.

(3) The Rio Scale is imprecise.

Absolutely true. An integer scale of zero to ten produces a result expressed to but one significant figure. Greater precision, though appealing to mathematicians, can be misleading. Take, as a case in point, the widely accepted value of "normal" for human body temperature: 98.6 degrees Fahrenheit. That soulds pretty precise. If a child's temperature measures 98.9, or maybe 98.3, might not a new parent be inclined to call the pediatrician in alarm?

Variations from "normal" are normal. In fact, the original study into "normal" body temperature was performed on the Celsius scale, and produced an average value of 37 -- that is, only two significant figures. Arithmetic conversion to different units resulted in the expression of a value in three digits, implying a misleading level of precision. And, since the span of a Celsius degree is almost twice that of a Fahrenheit degree, there's bound to be even more variation from patient to patient, hour to hour, and day to day, which the implied precision of the stated Fahrenheit norm completely obscures. So would it be with more Rio Scale digits.

(4) The Rio Scale is variable

Absolutely true. When an initial detection is made, we have but a single data point from which to draw a preliminary conclusion. As follow-up research is performed, and other observers brought into the analysis, opinions change. Variability is in fact a major strength of the Rio Scale -- it allows us to plot solutions over time, as more information is gathered, ultimately settling down to a value which we can generally accept as reasonable.

(5) The Rio Scale is ordinal.

Absolutely true. The difference in impact between a Rio 7 and a Rio 8 detection is likely quite different from the difference between a Rio 2 and a Rio 3. Doesn't matter. The only numbers we can really hang our hat on are the extremes. That is to say, nothing ever scores a Rio 10 until it's believed to be absolutely world-changing. And, once something is scored a Rio 0, it's believed to be meaningless. Anything in between is just tinkering at the margins.

(6) The Rio Scale trivializes the social consequences of contact.

With this one, I must disagree. Over its first three decades, SETI science made observations with no attempt to quantify their consequences. I believe that trivialized the social impact of contact. For the last two decades, we've been developing, and tweaking, an analytical tool for impact analysis. Any attempt at quantification, no matter how flawed, is a step in the right direction. I invite John Traphagan to join my colleagues and myself in the ongoing process of refining and perfecting the Rio Scale, so that it will ultimately shed more meaningful light on (in John's own words) "the social consequences of a very complicated potential event in the future of humanity that will represent a challenge from a social policy perspective."

What do you think? Please share your thoughts at

Disclaimer: The opinions expressed in editorials are those of the individual authors, and do not necessarily reflect the position of The SETI League, Inc., its Trustees, officers, Advisory Board, members, donors, or commercial sponsors.

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