John Leighton is director-general of the National Galleries of Scotland

YES: Attendance figures can be a useful guide to the impact of an exhibition but they need to be viewed alongside other measures such as audience feedback, critical reception and peer review.

In Edinburgh last year we experienced the risks involved in linking high attendance with success. Our summer show of the sculptures of Ron Mueck was a success and the local press dwelled on the throngs of visitors who came to admire these miracles in fibre-glass. At about 130,000 visitors, it was the highest attendance for a contemporary show in the UK in 2006.

Later in the year, we mounted a major retrospective of the work of Douglas Gordon. Without the festival crowds and in the winter, the show attracted a mere 12,000 visitors. The local press quickly branded the show a flop. We had hoped for more visitors but we were even more proud of this exhibition than its predecessor.

For the first time we had mounted a spectacular show of a leading contemporary Scot in our refurbished exhibition galleries in the heart of the city. The response from art critics was enthusiastic, with some rave reviews in the national and international press.

Attendance can be influenced by many factors, from timing to ticket prices and I have learned to be wary of the institutional adrenalin that kicks in when the box office is under siege. Yes, the crowds give us a buzz but they are not a reliable measure of 'good'.

Alan Borg is the chairman of the Foundling Museum, London

NO: Exhibition figures for 2006 reveal the UK hosted fewer high attendance shows last year than most other countries. Does this matter? Of course numbers are one measure of success, but only one.

A Japanese curator once told me that during a European loan show at his museum a young man came in when the gallery opened and stood in front of a painting by Cézanne for the entire day. When asked why he had done this, he said it was probably the only chance he would ever have to see this painting and he wanted to make the most of it.

We can't all show such dedication, but the message is clear - it is better for one person to have life-enhancing contact with one object than for thousands to pass through a show without really looking.

Great shows can change your life, open your eyes to new things and convey new ideas. This can be difficult to achieve as a visitor in a crowded blockbuster, when all you can do is peer over the heads of others.

The best show in London last year was the Victoria and Albert Museum's At Home in Renaissance Italy, which was well attended but not too busy. It was full of wonderful objects, scholarly insights, and a joy to behold.

It would be going too far to say that the real measure of the value of an exhibition is in inverse proportion to its popularity, but then I remember that you cannot get into Kylie because of the crush.