Holdings weighted values are in general more interesting than straight counts, as the holdings weight is a better indicator of how likely a field is to be relevant to actual searches.  

If an element is used in 300 records, but has 300,000,000 holdings, it seems to indicate a rarely assigned element that is nevertheless applicable to some  widely held items. 

If an element is used in 300 records, and has 300 holdings, it suggests a rarely assigned element that either is  used in a few records that describe unique items, or in is misapplied in  records which are not subsequently re-used.  

There does seems to be a slight bug in the way that these values are being computed:
For example in http://experimental.worldcat.org/marcusage/650.html ,

TOTAL Occurrences:            113,003,641
Subfield a occurrences:       279,078,783 (2.5 : 1)
Overall number of Holdings: 1,501,877,652
Subfield a holdings:        5,840,127,920 (3.9:1)

It seems that the total/overall counts are in terms of records, but the subfield counts are in terms of fields occurrences (if a record has two 650 fields with a $a, the subfield count will be increased by two, and presumably the holdings count by twice the number of holdings) . 

This does give some interesting information, in that it suggests that more common holdings have more subject headings assigned, but it doesn't let us compute what %age of records or holdings  that have at least one 650 use subfield $a . 

Field 245 shows some other curiosities: 
http://experimental.worldcat.org/marcusage/245.html

Subfield 245 $k has 469,891 occurrences, but only 427,311 holdings;  this suggests that there are records included in the counts which have zero holdings.  These might be worth filtering out. 

Simon

On Thu, Mar 7, 2013 at 10:11 PM, Tennant,Roy <[log in to unmask]> wrote:
It is the number of holding symbols attached to records that have that particular MARC element. For example:

Record 1 with the subfield: 10 holdings
Record 2 without the subfield: 30 holdings
Record 3 with the subfield: 50 holdings

Occurrences: 3
Holdings: 60

Roy



On 3/7/13 3/7/13 • 6:47 PM, "Karen Coyle" <[log in to unmask]> wrote:

  Roy, can you explain what the "number of holdings" figure represents? Is this a multiplier of the holdings on the records that have that field/subfield? (Sorry, I'm just having trouble wrapping my head around the variance in those numbers.)
 
 kc
 
 
 
On 3/7/13 4:33 PM, Tennant,Roy wrote:
 
 
MARC Usage: Additional report available Maria Oldal of The Morgan had requested to see $a and $2 combinations for the 655 field, so I was able to generate that and place a link on the page for that field: <http://experimental.worldcat.org/marcusage/655.html>. Although I will be somewhat limited as to the number of ad hoc reports like this I can generate, go ahead and request anything you want to see and I will see if I can get to it. Thanks,
 Roy