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Rarity Factors (RF) are used in many different specialties of philately. In most cases, their development has been tailored to meet the needs of the specialty in question. It is acknowledged that RF can be useful but need to be used with caution. A good understanding of the subject matter is often essential. As a service, BNAPS offers below a summary of RF definitions for several specialties. Others are encouraged to join in, and can do so by consulting the BNAPS webmaster. BNAPS and the webmaster can assume no responsibility for any mis-use or misunderstanding of these presentations. REGISTERED MAIL click here. PERFINS click here. RPO click here.
George Arfken has submitted the rarity scale used in Horace Harrison's publication: "Canada's Registered Mail, 1802 - 1909". The heading reads: "We have been asked to include estimates of the rarity of the various proofs, stamps and covers illustrated in this book. Accordingly, we have adopted and used the following scale:
Exceedingly Rare, no more than three - - - - RRR The rarity factor is shown at the end of the figure caption. Readers should understand that all assignments are based on copies "known to us." Also, there may be a number of covers in the lowest categories which have a significant postal marking, making that particular cover a higher rarity to collectors of that specialty. For example, a cover to the U.K. might well be in the R category, but a "CANADIAN PKT" date stamp could move that particular cover into the RR category." The rarity of a perfin pattern is not the same as the rarity of a particular stamp with that pattern. The following is based on the section: "Perfin factors" in the "Canadian Stamps with Perforated Initials" handbook , copyright 1985 of the BNAPS. The rarity of a Canadian perfin pattern was determined in a 1980-82 survey of the holdings of the members of the Perfins Study Group of BNAPS of both postage and revenue stamps. The system is logarithmic as follows:
A 1-3 reported If there are three perfins with Rarity Factor A, and each stamp is a different issue, then each of these three perfins is the only one like it in the world. The rarity of a particular issue of a pattern can best be judged from the length of time the pattern was in use as that determines the number of issues upon which the pattern can be found. Another consideration is whether the company sent mail locally, nationally and internationally. Finally, some companies instructed their personnel to place only the pattern on the stamps in one position, which makes alternative positions extremely rare. Others didn't care, and their patterns can be found in all eight possible positions on the stamps. Finally, when stamps were printed in quantities of 400 on a sheet which was then cut into 4 sheets of 100, two edges of each such sheet were straight and thus out of each 400 stamps such as the 'Admirals", there were 32 with a straight edge at on of the four sides of the stamp, and there were four with two straight edges each, meeting at one of the four corners of the stamp. It is theoretically possible to collect eight different straight edges and one centre stamp without straight edges for a total of nine perfins for each of the eight perfin positions that are possible, for a total of 72 different perfins for each issue that had straight edges. Even for perfins with a rarity factor I this has not been done due to the scarcity of material. In countries with populations larger or smaller than Canada, the Rarity Factors for their perfins are calculated differently, if at all. RAILWAY POST OFFICES (RPO) The following is taken (with some summarization) from "Catalogue of Canadian Railway Cancellations and Related Transportation Postmarks", by Lewis M. Ludlow (1982). This catalogue is due for a revision and any changes to this structure will be noted in due course. "The definition of Rarity Factor is fundamental; in the context of this catalogue, Rarity Factor of any given listing represents its relative relationship of scarcity to any other of the approxinate 3,000 listings, as expressed by their own Rarity Factors. From this definition, it follows that three basic elements should be used to establish this independent relationship of any one listing to any other:
Ludlow then describes in detail how the three factors were employed, using statistical help. The conclusion states: "The statistical formula derived from these three elements has been extrapolated across a log/log scale ranging from "5" for the most common to "500" for the normally most rare. This breadth of scale has been chosen to allow finer gradations of difference to be defined in whole numbers, rounded to the nearest "5". These narrow shades of distinction have a high degree of validity when it is emphasized that these Rarity Factor results come from statistical calculations and that they represent relative relationships within the listings. Many of the Rarity Factors have been suffixed by an asterisk (*). When an asterisk has been added to an RF of 500, it indicates that the statistical calculation has yielded a result of rarity sufficiently above 500 to be well off the scale, and that its relative relationship cannot otherwise be defined. Periodically, the Rarity Factor number is followed by a cross-hatch mark (#). Such marking is an indication that most existing strikes of this listing have been created as favors for collectors and did not originate through recognized postal channels. No Rarity Factor is assigned for any unconfirmed listings, or for any entries known only from their proof strikes or destruction order strikes. There is not necessarily a direct correlation between Rarity Factor and the value of a cancellation. [It goes on to point out that the quality of a strike is a significant factor. ] In the final analysis, the worth of a cancellation is a value judgment between individual buyer and seller, and is beyond the scope of this book." EDITOR'S NOTE: One of the key factors in the above description is the reference to RPO "listings". Many listings include numerous separate hammers, some of which are far more common than others. The inclusion of RF for each hammer would be a monumental, likely impossible, task. |