When a government loses a nation's respect, it is not individual politicians alone who fall from favour: the ideas they bring with them, too, may become tainted by association.

One such casualty has been highlighted by the current row over standard assessment tests - or SATs - in schools. Suddenly everyone is sneering at the idea of assessment. The sneers are part of a pattern of criticism that includes (for example) health service targets, targets for police arrests, the ranking of local authorities and star-ratings for hospitals. League tables, targets, tests and rankings are falling out of fashion.

The pattern is dubbed the “target culture”: dirty words these days. Implied in the belief in targets is that success in the delivery of public services can be be measured; and that excellence is quantifiable. Such measurements underlie performance ratings for public institutions, and the carrots and sticks by which they are regulated. This is the philosophy that is now suspect among conservatives and professionals alike.

The reasons are not surprising. The targets politicians have set have often been crude - driven by a desire for easy headlines, not for the most effective means of raising standards. Obviously if you make headline hospital waiting lists your trumpeted target you may distort health workers' efforts, encouraging deception, and spawning sly ruses for keeping patients off the published lists. Obviously, if in an effort to assess teachers' performance you test children repeatedly and oppressively from an early age, you may reduce the time spent teaching; and find children learning only how to sit tests. Obviously if you assess local authorities under the headings of a small number of performance categories - rubbish collection, leisure facilities, parking services etc - you may encourage them to neglect those functions not assessed. Oversimplification, misdescription and political posturing bring such assessment into disrepute.

But bad targeting should not be an argument against all quantitative analysis. Good and bad, the whole idea of published measurement of the quality of public service is now falling into disrepute. “How can you measure care?” people ask; “How can you quantify sympathy? How can you calibrate the performance of an arts body, the comforting manner of a doctor, the common sense of a police officer, or the child-focused skills of a teacher with a problem kid who will not be well served by being pushed to take exams?”

Fair questions, all. The answer, though, is that we must never give up trying. Across a wide range of the “delivery” of public services, measurement must always be a messy, sometimes imprecise, often hit-and-miss and occasionally unfair business, but there is no alternative. It is not enough to thumb our noses at unintelligent targeting. When public money is spent it is government's duty to get value for it. The money is disbursed in measurable amounts. Value must be assessed in the same way.

It was really John Major's government and his “Citizen's Charters” that sharpened the drive to see the public as customers for public services. Where the customers of the State had limited real choice, and free-market competition could not be relied on to keep providers on their toes, the idea was to publish aims, establish standards of service, and try to measure performance in attaining them. Labour governments have shared this thinking enthusiastically. I believe their instinct to quantify has been sound, even if sometimes translated into crude or counter-productive policy.

The “how can you measure... ?” brigade are riding high at present, but we should be suspicious of them. Listen carefully to the objections that some educationists and teachers' unions are raising to the SATs and you will hear - behind the obvious complaints about excessive testing - something close to an objection in principle to external testing: the “How can you compare chalk in Portsmouth with cheese in Pontefract?” sorts of argument. Worse, you will hear the view that nobody is better qualified to assess a school class's performance than its own teachers. This is nonsense, but seductive.

We should be on guard against what are, at heart, reactionary views. The case for the essential unquantifiability of the more sophisticated forms of public service too easily becomes a professional conspiracy against the taxpayer, unconsciously calculated to featherbed a quiet life for public servants. Did you know, for instance, that schools and class teachers have to be given advance warnings of outside inspections? This is outrageous; but try inveighing against it, and see what support you get from the professionals.

Half of Britain has always had its performance measured and been paid according to the results, with few excuses taken. The labourer, the machinist, the cleaner - the working classes - have seldom been allowed the “How can you measure...?” plea when their work comes to be assessed. Assessing a bricklayer is a rough-and-ready business: how many courses of bricks per hour? He too could make arguments about the perverse effects of a targets culture; but we would be impatient with them.

It's a pity the white-collar classes don't apply the same rough justice to assessing themselves. “How can you measure...?” is a charter for loafers in any organisation. Have you noticed how the cry of “quality can't be quantified” tends to come from the professions? From the lips of doctors, lawyers, architects, university lecturers, public service broadcasters and schoolteachers, the lament that targets or - Heaven forbid - assessment would have a brutalising effect upon their work, has slipped easily from the tongue.

From this special pleading we columnists are not exempt. Doubtless I could frame for you an argument that the worth of a column can be weighed - if weighed at all - by considerations deeper than whether many readers can be bothered to read it in the first place. But I wouldn't. Editors must try, however imperfectly, to define their market. They must research, however approximately, the extent to which they are reaching it; and any writer who forgets that he writes to be read, and that success is measurable, misunderstands the animating spirit of English writing.

Without targets, how do we ensure that public servants aim as we direct them to? Without measurement, how can we tell whether things are getting better? Without tests and exams, how can we try to see that parents and children across Britain are not served patchily? What can be measured must be central to the way we regulate, motivate and discipline our public service. What cannot must be viewed with suspicion.

Overenthusiastic quantifiers will sometimes make silly mistakes, and these will be seized on by the “How can you measure...?” brigade. Its arguments will be shrewdly self-serving: advanced by producer interests masquerading as defenders of the customer's interests. We should resist them. Customers for public services, trapped by monopoly provision, depend utterly upon the State's techniques of assessment. Assessment depends upon measurement. What we cannot at least try to measure, we should not ask taxpayers to fund.

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