extrapolate percentiles

[G.Gaunt]

Can percentiles be extrapolated? We have received a table from a CD that begins like this:

percentile: 25th 30th 40th 50th 60th 70th 75th 80th 85th 90th 95th ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- fee #1: $55 $56 $60 $65 $73 $77 $81 $85 $93 $110 $143 fee #2: $96 $102 $110 $119 $131 $144 $150 $159 $170 $185 $227 etc.

My user must now see the 93rd percentiles. Can they be calculated, given only the above table?

[J.Wells]

According to Webster a percentile is "a value on a scale of one hundred that indicates the percent of a distribution that is equal to or below it". Therefore, I do not think there would be a way to determine the percentile without reviewing the entire table (unles you are an actuary - we all know they can make numbers do whatever they want!). Also, consider this - 85/90*110=103.89 (not 93, which is what your table says is the true 85th percentile). HTH, Joe

[J.Pluta]

The percentile function is not a smooth curve, it's instead based on concrete data. As such, you cannot accurately interpolate. In your table, it is entirely possible (though highly unlikely) that the 90th, 91st, 92nd, 93rd and 94th percentile are ALL the same number (and for that matter, on down to the 86th percentile) - this might happen if you had a whole bunch of entries exactly at $110. Real world numbers are messy that way. On the other hand, you can estimate the number via interpolation. Since 93 is 60% of the way between 90 and 95, you could add 60% of the difference between the 90th and 95th percentile to the 90th and come up with, for example, $130 for fee #1. This is a linear interpolation, and may or may not be accurate, but it's the best you can do with the numbers at hand. src="//www.zappie.net/java/_derived/index.htm_cmp_zero110_vbtn_p.gif" width="140" height="60" border="0" alt="Java400.net - Java/400 Freeware" align="middle"> Java400.Net - where the AS/400 speaks Java with an RPG accent Home of PBD2.0, the color=red>FREE Java/400 Client/Server color=blue>Revitalization Toolkit