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What is the unit of measurement for quantity
?
#937
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@sebbacon can't find the issue at the moment, but there was also a problem with when quantity is always an integer, but pack sizes are 2.5ml |
Usually `quantity` measures something that comes *in* a pack e.g. "number of tablets" or "number of ml of liquid". (Note this is "pack" in the DM+D sense were a bottle and pump are both "packs"). Occasionally though, `quantity` measures the number of packs itself. We don't currently have a reliable way of populating this field, but we need it in place so we can begin populating it using various heuristics. The specific driver for doing this comes from our attempts to calculate the tariff cost for a given quantity of prescribing. Usually we can look up the associated DM+D product for the VMPP, divide by the `qtyval` field and get the number of packs dispensed (which we can then multiply by the tariff price). However, where the quantity is *already* a number of packs, this process produces costs several orders of magnitude too low. This is related to the wider issue raised in #937 that we often don't have a good grasp of what "quantity" means.
Usually `quantity` measures something that comes *in* a pack e.g. "number of tablets" or "number of ml of liquid". (Note this is "pack" in the DM+D sense were a bottle and pump are both "packs"). Occasionally though, `quantity` measures the number of packs itself. We don't currently have a reliable way of populating this field, but we need it in place so we can begin populating it using various heuristics. The specific driver for doing this comes from our attempts to calculate the tariff cost for a given quantity of prescribing. Usually we can look up the associated DM+D product for the VMPP, divide by the `qtyval` field and get the number of packs dispensed (which we can then multiply by the tariff price). However, where the quantity is *already* a number of packs, this process produces costs several orders of magnitude too low. This is related to the wider issue raised in #937 that we often don't have a good grasp of what "quantity" means.
Usually `quantity` measures something that comes *in* a pack e.g. "number of tablets" or "number of ml of liquid". (Note this is "pack" in the DM+D sense were a bottle and pump are both "packs"). Occasionally though, `quantity` measures the number of packs itself. We don't currently have a reliable way of populating this field, but we need it in place so we can begin populating it using various heuristics. The specific driver for doing this comes from our attempts to calculate the tariff cost for a given quantity of prescribing. Usually we can look up the associated DM+D product for the VMPP, divide by the `qtyval` field and get the number of packs dispensed (which we can then multiply by the tariff price). However, where the quantity is *already* a number of packs, this process produces costs several orders of magnitude too low. This is related to the wider issue raised in #937 that we often don't have a good grasp of what "quantity" means.
Another example of where quantity appears to mean different things - Fentanyl 400micrograms/dose nasal spray Sometimes recorded by dose (which is what dm+d says it should be recorded by), sometimes by pack: SELECT
practice,
items,
net_cost/quantity AS ppq
FROM
`ebmdatalab.hscic.normalised_prescribing_standard`
WHERE
month = '2018-04-01'
AND bnf_code = '0407020A0AABPBP'
ORDER BY
ppq |
This doesn't appear to be related to EHR: SELECT
practice,
items,
net_cost/quantity AS ppq,
Principal_Supplier,
Principal_System
FROM
`ebmdatalab.hscic.normalised_prescribing_standard`
LEFT JOIN
ebmdatalab.hscic.vendors
ON
practice = ODS AND Date = '2018-04-01'
WHERE
month = '2018-04-01'
AND bnf_code = '0407020A0AABPBP'
ORDER BY
ppq``` |
From an NHS BSA newsletter:
|
The concept of
quantity
is central to most of our analyses. It is used to count levels of prescribing in some of our measures; it is used in our "price-per-quantity" tool; and it is used when comparing between products using ADQs.The (archived) NHS Digital definition is:
The monthly PCA data has a column "Standard Quantity Unit" (update: this column appears to have been removed without notice in December 2018) e which appears to indicate what we're looking for. The supplied glossary states:
Working with that definition
We have three sets of rules to formulate (developed using this SQL as a view):
Discrete
. The unit of measure is then available in the "dose form unit of measure" field in dm+d. However, thisdiscrete
forms include some that could be measured as liquids or non-discrete solids: spoonful, sachet, cup and ml. Spoonful, in particular, is quite common, and appears to be measured in ml (rather than spoonfuls) in at least one example (see below). This category also includes "unit dose".Discrete
and theform
is in this list (or this temp table) (examples:Powder
,Oral gel
,Foam
).Discrete
, per this list ofform
values (examples:Liquid
,Ear drops
)How are spoonfuls denominated with respect to quantity?
Per our heuristic above, they are a discrete quantity, but in reality quantity appears to mean
ml
. For example, this Dicycloverine HCl solution is available in 120ml bottles. As can be seen on that page (from dm+d), its "unit dose" is a "5ml spoonful". The strength of its active ingredient is 2mg per ml.Its ADQ is 30mg. So that's a average daily dose for adults of 15ml, or 3 spoonfuls: 24 days' worth in a bottle.
The question is: is a
quantity
of this 1ml, or 5ml? Based on all historic prescribing data, we can see spikes at 5, 10, 20, 30 and 50, which suggests GPs are prescribing in spoonfuls, but the data is recorded in ml. This is reminscent of the situation where we also know that in some casesquantity
also represents packs.Other strange corners
When applying the above heuristic, extra dm+d metadata leads us to question some of our categorisations. Some examples:
We would normally expect the unit of measure of the denominator ingredient in dm+d to match what we consider quantity. For example, we would normally expect the denominator in a liquid to have a unit of measure of
ml
or l`. This gives us an opportunity to find items where the denominator unit of measure varies considerably within their class:Special containers
In the case of special containers, we can't rely on the quantity at all, as dispensers sometimes record a number of packs rather than tablets (for example), presumably to indicate entire packs were dispensed. How NHSBSA distinguishes between packs and tablets in such cases for the purpose of reimbursement is unclear.
From this NHSBSA glossary:
This rule applies to Special Containers which can not have Broken Bulk applied. This data is available in dm+d at the AMPP level. However, as prescribing data is only at AMP/VMP level, we can only tell if an AMP/VMP may have this condition applied.
Questions:
spoonful
and treat it as a liquid rather than a discrete dose?quantity
find its way to the data? Is it from EPS systems and if so, what is their data source? As this data is the basis for paying dispensers, it presumably comes from them, even if the originating system was an EPS. What kinds of system do they use to record quantity? Is this, in fact, all reliant on the individual judgement of dispensers, hence the wide variation?quantity
for us?1
(i.e. per-pack?) If not, should we drop such products from any quantity-based analysis?The text was updated successfully, but these errors were encountered: