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Billboard Year-End charts are a cumulative measure of a single or album's performance in the United States, based upon the Billboard magazine charts during any given chart year. Billboard's "chart year" runs from the first Billboard "week" of December to the final week in November, but because the Billboard week is dated in advance of publication, the last calendar week for which sales are counted is usually the third week in November. This altered calendar allows for Billboard to calculate year-end charts and release them in time for its final print issue in the last week of December. Prior to incorporating chart data from Nielsen SoundScan (from 1991), year-end charts were calculated by an inverse-point system based solely on a title's performance (for example a single appearing on the Billboard Hot 100 would be given one point for a week spent at position 100, two points for a week spent at position ninety-nine, and so forth, up to 100 points for each week spent at number one). Other factors including the total weeks a song spent on the chart and at its peak position were calculated into its year-end total. The same method was used for albums based on the Billboard 200, and songs appearing on the other charts (e.g. Hot Country Singles).
After Billboard began obtaining sales and airplay information from Nielsen SoundScan and Nielsen Broadcast Data Systems, the year-end charts are now calculated by a very straightforward cumulative total of yearlong sales (or sales and airplay) points. This gives a more accurate picture of any given year's most popular titles, as an entry that hypothetically spent nine weeks at number one in the spring could possibly have earned fewer cumulative points than one spending six weeks at number three in January. Due to this methodology, albums at the peak of their popularity at the time of the November/December chart-year cutoff many times end up ranked lower than one would expect on a year-end tally, yet are ranked on the following year's chart as well, as their cumulative points are split between the two chart years.
Between 1959 and 1963 the chart was divided in a stereo chart and a mono chart and were named Best-Selling Stereophonic LPs and Best-Selling Monophonic LPs (1959–1960), Stereo Action Charts and Mono Action Charts (1960–1961), Action Albums—Stereophonic and Action Albums—Monophonic (1961) and Top LPs—Stereo and Top LPs—Monaural (1961–1963).
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