Sir - You report (October 12) that the Audit Commission has awarded its top four-star rating to South Oxfordshire District Council, while the Home Office has graded Thames Valley Police as "second worst in the country". For those of us still getting over the shock of the four-star award to Oxfordshire County Council, the big question is: how reliable are these assessments?

Usually, they are based on indicators devised by accountants in the belief that performance can be assessed by numbers. Targets are invented and used to define compliance.

But what is convenient to measure may not be what is best to do.

At a hospital in Kent, treatment targets (to which funding was linked) were given priority over cleanliness; many patients have since died from infections. In some police forces, officers have to meet monthly targets for convictions; those that are easier to process may not be the most important.

In schools, choosing softer subjects will improve exam results, but science, maths and languages enrolments are declining. A high rating might conceal serious deficiencies, and a low rating might be less than fair.

Thames Valley Police point out that although working days were unavoidably lost through terrorist investigations, crime in the region has in fact fallen by six per cent this year.

To citizens, tackling crime certainly takes precedence over pursuing targets that might be ill-conceived or over-ambitious. Whatever the reason, one can sympathise with the disappointment of the police at their Home Office grading.

Attempting to measure the performance of people and organisations has been described as the quickest way to lower everyone's morale.

These crude efforts by the Government to calibrate public services may well do more harm than good.

Maurice Holt, Oxford