Can we trust BARB’s viewing figures for Sgorio on S4C?

Yesterday The Telegraph printed a story about S4C viewing figures for the football programme Sgorio:

Sgorio – Welsh for score – turned into a no score draw on the night despite regularly pulling in tens of thousands of viewers on other nights.

It is a regular show on Channel Four in Wales featuring top matches from the German, Spanish and Italian leagues.

Under the TV rating system, any programme with fewer than 2,500 viewers is regarded as “making no impact”.

Today the Western Mail ran a very similar story. Before we get into a discussion about what this might mean, let’s examine the figures. According to The Telegraph:

The figures were compiled by the Broadcasters Audience Research Board.

The body surveys viewing habits of 11,300 viewers in 5,100 British homes, and weights them according to the rest of the population.

How many homes own television sets in the UK? Let’s use BARB’s own figures:

In 2009, 25.9 million homes own at least one television set out of a total of 26.6 million homes in the UK.

Let’s concentrate on television-owning homes. According to this 97% of homes in the UK own a television.

The 5,100 British homes is 0.02% of the homes that own a television. BARB is collecting these figures by sampling one house in every 5000 television-owning houses in the UK, roughly speaking.

That may be adequate for popular programmes but is it enough to gauge the popularity of a minority language programme?

S4C publishes a top 20 chart. It would be good to have figures for other special interest programmes for comparison, but BARB doesn’t publish these figures free of charge. (Subscribe if you want.) Regardless, how meaningful are these figures in light of the sample size? I’m not aware that BARB has more fine-grained techniques for sampling S4C viewing, anyone know?

How many people live in Wales and in the UK? Let’s take the population figures from the Office for National Statistics:

Wales: 2.9 million
United Kingdon: 59.8 million

Let’s now look at sampled viewers. BARB’s sampled viewers make up a proportion of the total number of viewers in the UK. Let’s assume BARB has picked a fair distribution of sampled viewers in Wales. We could then expect the proportion of sampled viewers in Wales to match the proportion of the UK who live in Wales.

As a proportion, Wales makes up 4.8% of the UK population. Therefore we would expect BARB to have sampled approximately 548 viewers in Wales (which is 4.8% of 11,300).

I’m going to make an assumption here. I’m going to assume that out of the 2.9 million people in Wales, 97% have access to a television in their own home. This reflects the 97% of households who own a television in the UK. Therefore we calculate that around 2.8 million people in Wales have a television in their own home. My aim is to get an approximate impression of the scale here – the order of magnitude – to decide how trustworthy the statistics are. The figures may be slightly off, so please let me know if you have more accurate figures.

Therefore, each sampled viewer in Wales represents roughly 5000 of the television-watching population in Wales. This is similar to the figure for households above. I’m also assuming S4C’s heartland is Wales, although it is sometimes available in households outside Wales.

BARB’s threshold is 2,500 viewers for a programme “making an impact”. These are not real viewers, but figures extrapolated from the comparatively tiny sample size.

So according to this analysis, the conclusion that Sgorio made “no impact” rests on just ONE of the sampled viewers in Wales.

Again, is this enough to measure the reach of a programme, in particular one in a minority language?

UPDATE 21/10/2010: Comments are off but trackbacks and pingbacks are on.