More or Less was broadcast on Tuesday, 4 March, 2003 at 1600 GMT on BBC Radio 4.

 Click here to listen to the programme

From chemicals in our food to the threat of gas attacks or terrorists poisoning our water, we often live in fear of the toxic.

And recently there was a warning about the dangers posed to pregnant women by mercury in tuna.

More or Less looks at the way we define toxicity and the crucial role played in that definition by quantification and concentration.

Toxicity, it turns out, is often all in the measurement.

We talked to arch sceptic, Stephen Milloy, writer on 'Junk Science', about the way scientists identify potential toxicity and to Michael Joffe, epidemiologist at University College, London.

Census

How can there be an argument about whether or not nearly a million people in the UK exist?

The latest results from the Census have caused fierce controversy and may result in the loss of millions of pounds of government grants to some inner city local authorities.

Although the Census has its problems, it is now producing a wealth of information about every neighbourhood in Britain.

More or Less heard from:
Sandra Henderson, Westminster resident;
Monica, enumerator in 2001 Census;
Len Cook, registrar general, Office for National Statistics;
Tony Travers, Director of the Greater London Group at the LSE;
and Kit Malthouse, Deputy Leader of Westminster Council.

Bus numbering

Since the introduction of the congestion charge in London, it is expected that Londoners, at least, will be catching more of them.

But why are buses numbered the way they are?

More or Less looks into the history of bus numbering.

Travelling from London to Somerset, we search for meaning, and also talk to the man who uses bus numbers as an aid to memory.

And there is a none-too-serious warning about the number 94 in Taipei.

So if you ever catch that bus, don't miss More or Less.

We spoke to:
Robin Lodge, Vicar of All Saints Church, Rockwell Green, Somerset;
Sheila Rabson, organist at All Saints;
David Ruddom, compiler of database of bus routes for London Transport Museum;
and Paul Jenkins, of First Bus company, Somerset.