In the New Yorker article discussed in an earlier post about leaf-blower noise, Tad Friend wrote that "a Berkeley psychiatrist […] addressed the problem's demographic valence", describing an attempt to rebut the idea that anti-blower activists are "just some fat-ass fussy busses, rich white people in the suburbs, worrying about a little noise". Mark P noted in the comments that
I have never seen the term "demographic valence." I'm familiar with the term "valence" in chemistry and home decor. I can see how it could mean something like "attractiveness." But in this context, I have to assume that it means the tendency of noise to be a problem within different demographic groups.
Valence actually has a broader and more interesting history, and Tad Friend's use seems to be an extension of an existing class of meanings that Mark P may not have encountered before.
The original source was Latin valentia meaning "bodily strength, vigor" or "capacity, endowment". According to the OED, in the 15th century it was borrowed into English as valence meaning "an extract or preparation (of some herb) used in medicine". In the 17th century, it appeared as both valence and valency, meaning "valour, courage" or "might, power, strength". In the late 19th century, both valence and valency were used (along with quantivalence and atomicity) to translate German Quantivalenz, meaning "The power or capacity of certain elements to combine with or displace a greater or less number of hydrogen (or other) atoms".
In the early 20th century, the psychologists stepped in, using valence to mean (in the OED's gloss) "Emotional force or significance, spec. the feeling of attraction or repulsion with which an individual invests an object or event". Merriam-Webster's gloss for this sense is "the degree of attractiveness an individual, activity, or thing possesses as a behavioral goal", related to another sense given as "relative capacity to unite, react, or interact (as with antigens or a biological substrate)".
And at some point, linguists made a play as well, using valence to mean something like "The number of grammatical elements with which a particular word, esp. a verb, combines in a sentence". That gloss comes from the Google dictionary.
Encarta reorganizes this in terms of a shared notion of "combining power":
1. combining power of atoms: the combining power of atoms or groups measured by the number of electrons the atom or group will receive, give up, or share in forming a compound
2. combining antigenic determinants: the number of different antigenic determinants with which a single antibody molecule can combine
3. combining power of verb: the ability of a verb to combine grammatically with noun phrases in a given clause
The psychologists' meaning is left out, and can't easily be expressed as a fourth clause in this pattern. "The combining power of behavioral goals" isn't quite right as a way of describing the (positive or negative) degrees of attractiveness that psychological valence denotes.
Tad Friend's usage — "the problem's demographic valence" — apparently means, as Mark P inferred, something like "the degree to which the problem affects or concerns different demographic groups". This may represent semantically bleaching causation out of the notion of "combining power", leaving simply "pattern of association". (Though it's possible that Friend really did mean "the problem's demographic combining power" rather than "the problem's demographic pattern of association".)
As for the putative role of valence in home decor, Mark P has merged two historically separate words here. The conventional spelling for "a short drapery or wood or metal frame used as a decorative heading to conceal the top of curtains and fixtures" is valance. The etymology of this word is obscure, according to the OED, but may come from Old French avaler "to descend", which would make it a relative of avalanche; in any case, L. valentia is not in the picture. (Earlier particular interpretations of the same core concept are glossed by the OED as "A piece of drapery attached lengthways to a canopy, altar-cloth, or the like, so as to hang in a vertical position", and "A border of drapery hanging round the canopy of a bed; in later use, a short curtain around the frame of a bedstead, etc., serving to screen the space underneath".)
[Update — a bit of search suggests that valence has come to be used in academic writings about literary topics to mean something like "association", "connection", or "interpretation", often with modifiers like religious, political or ideological. This is probably where Friend picked it up. Some recent examples from articles in the journal Studies in the Novel:
Arguably, he is simply attempting to illuminate an unacknowledged religious valence within certain widely accepted literary and critical gestures, but McClure's concept of the religious at times seems too broad, so as to relinquish all specific meaning.
Resistance is as far as she was able to go, and though we cannot make her do more, we have yet to register the political valence of her susurrous grotesque.
Further, we can-and I think should-read Member as a "lesbian coming of age" novel (Kenschaft 229; see also Lynch) while also reading it as queer-affirmative in its contemporary, "multipl[y] valence[d]" sense (Adams 554).
Thus, trauma is both an immediate experience, a wounding, and the belated effects of that wound. This double valence of the term "trauma" lends it the potential for an expansive temporal longevity.
A girl who can build a church is admirable, but she is not a pattern-card of "ladylike" behavior. The unstable ideological valence of the church-building project is symbolized through the associated trope of vision that runs throughout the novel.
I searched Studies in the Novel from 1973 forward, and the first of 27 instances of valence was in 1991, used in what might be the psychologists' sense:
Though the return to the Manse exiles the narrator from a carefree life united with nature, he argues for its necessity, that is, the necessity of a sense of self as a subject, bound to social institutions. After his return from nature he insists upon transforming the valences of the experience by making a case for a new socialized status. "How sweet was it," he declares, "to return within the system of human society, not as to a dungeon and a chain, but as to a stately edifice, whence we could go forth at will into statelier simplicity!"
However, the chronologically second hit, in 1994, seems to be the new litcrit "association" or "interpretation" sense:
Godbole's unsolicited awareness of Mrs. Moore articulates a narrative method according to which an event transpires in a transcendentally significant way (a "telepathic appeal") and at the same time takes place for totally insignificant reasons (the result of "chance," a mere "trick of his memory"). […] In every case, the narrative events which have this double valence of the supernatural and the aleatory are attached to Mrs. Moore.
And the next 24 are similar. Perhaps it's time for a "sense induction ceremony" at the OED.]