A Differential Assessment is the calculation of the difference in values for the same kind property in the same kind of neighbourhood in different parts of the country. It’s used in the relocation process to establish the level of allowance to be paid to someone who is relocating from a low to high cost housing area. For instance, if someone is relocating from Liverpool to London, it is likely to cost more to purchase the same kind of house in the same quality of neighbourhood.

A Differential Assessment will calculate the difference and that will usually form the basis of some form of compensatory allowance.

There are several methods available. The main ones are:

HomeMatch
Created in 1991 by cosmetically adapting Experian’s Mosaic neighbourhood classification software, it was the forerunner of the ‘sophisticated’ use of geodemographic information systems (GIS) to compare locations. Basically unchanged since its inception, it is dependent on the technical ability of the software’s operator and the accuracy of the destination area valuation.
Verdict: OK. Lack of development, in particular in its presentation, makes it dated – 5.5/10

Locate4000-9000
Like HomeMatch, it is an adaptation of an off the shelf marketing package (called ACORN). Has the edge because it has been developed over the years and ACORN contains more property data than Mosaic. Also, as it was originally created ‘for purpose’ from raw housing data, the resultant ‘like for like’ property tables are fairly accurate. Currently operated under licence (and possibly a different name) by Property, Relocation and Search Consultants Ltd (confusingly billed as PRSCO Ltd), which claims to have been founded in 1993. However Companies House records it as having been formed in January 2009, which would tend to put question marks over any claims of accuracy. Again, only as good as the people operating it.
Verdict: The best use of GIS software to date but has stagnated over the last few years and is unlikely to develop further – 6.5/10

Cartus Like4Like
As with Locate4000, Like4Like uses ACORN, but that’s where the similarity ends. In this case ACORN is a veneer of sophistication in the process, because its use to compare areas is extremely limited. Due to lack of technical expertise, the ability of the analysis software to pinpoint small geographic areas is redundant, rendering the resulting valuations highly suspect, which is a pity, because these tend to be drawn from the Hometrack database, a well respected source of property valuation data.

Verdict: Indifferent. Classic case of over promising and under delivering – 4/10

Traditional Property Tables

Beloved by the Public Sector and using spurious average property prices from the Land Registry or the Inland Revenue’s District Valuers’ Office, these tables are the most inaccurate way of establishing regional property price variations. Operated by the intellectually challenged, who take comfort from the source of the data, rather than applying some intelligence to how they are actually used, these tables have provided more over-payments of housing allowance then all the other methods combined. Any accuracy is purely coincidental and is as predictable as the Lottery. (Should not be confused with ‘like for like’ tables where values have been filtered through a GIS neighbourhood classification system.)
Verdict: Differentials for HR simpletons, great for relocating employees – 0.5/10

Others
Most other methods (including those operated in house by other Relocation Management Companies) tend to be cut down ‘me too’ versions of those described above.
Verdict: Cheap and cheerful and difficult to justify – you get what you pay for. 3/10