The Woman Who Regressed to the Mean

In The Sun, an article begins:

DOCTOR Who has lost a quarter of its viewers as many blast “politically correct” storylines since Jodie Whittaker entered the Tardis.

The Daily Mail makes similar comparisons.

This article looks at what has happened to Doctor Who ratings, from this series and previous incarnations of The Doctor since the 2005 revival.

In short

Whittaker’s debut topped the charts: Jodie Whittaker’s full debut topped the weekly viewership chart: with 10.96m viewers in 7 days.

Relatively high level of viewers: For its first six episodes, Series 11 has the second highest average viewership of all revived series of Doctor Who.

Regressed to the mean: The first episode of Series 11 was watched by more people than usual, and subsequent readings have been more typical.

Viewers in Time and Space

Doctor Who is a science fiction programme about a time-travelling alien and their human companions. The Doctor is a Time Lord, who can ‘regenerate’ when they die, meaning the role can be recast.

Jodie Whittaker’s first full episode as The (Thirteenth) Doctor was The Woman Who Fell To Earth, estimated to have 10.96m viewers in 7 days by the Broadcasters’ Audience Research Board (BARB).

This figure includes laptop, tablet and mobile viewings, and topped the ratings for 1st — 7th October 2018. Unlike previous series, Series 11 is initially broadcast on Sunday.

This was only the third time since the 2005 revival where Doctor Who has topped the weekly charts. The last time was in 2013, with the anniversary special episode The Day of the Doctor.

The Long Game

We can compare Series 11 viewing levels to those of past series — excluding special episodes, such as at Christmas.

It is clear Doctor Who series tend to decay in viewership.

In terms of its first six episodes, Series 11 (starring Jodie Whittaker) has an average of 8.64m estimated viewers per episode. This is the second highest of all revived series so far.

For the first six episodes, Christopher Eccleston’s Ninth Doctor (Series 1) achieved 8.65m viewers per episode. In Series 2, David Tennant’s starting run attained a slightly lower average viewership of 8.49m.

Matt Smith’s Eleventh Doctor received 8.13m viewers per episode in Series 5. Peter Capaldi’s iteration had the fewest: with 7.43m in Series 8.

Relative Dimensions

There has only been one revived series where viewers for its final episode exceeded the first: Series 4. The series finale, Journey’s End, followed a major cliffhanger:

Setting the first episode of each series to 100, a viewer index shows general decline.

The relative decline by the sixth episode is generally greater in series that had higher viewers in the first episode.

This is what statisticians call ‘regression to the mean’: an outlying reading is likely to be followed by more typical measurement.

Both Christopher Eccelston’s first episode (the return of Doctor Who) and Jodie Whittaker’s first full adventure exceeded 10m viewers. In Eccelston’s case, viewer figures generally tailed off throughout that returning series — finishing beneath 7m.

Also, it is the first time since the revival that Doctor Who has been a top four weekly BBC1 programme for every one of its opening six episodes.

Journey’s End

Looking at BARB viewer data, The Woman Who Fell to Earth received over 10m viewers. As in previous series, that high level for the series opener has not been maintained.

After six episodes, Jodie Whittaker’s time in the TARDIS performs well against all previous Doctor Who series since 2005 in terms of viewership and rankings.

We should wait for the series to finish before fully analysing its performance.

This article uses Broadcasters’ Audience Research Board 7 day viewer estimates: the number of people who watched programmes and channels within seven days of broadcast. These figures are survey estimates, subject to numerous sources of error, including sampling variation.

News articles typically use ‘overnight’ viewer figures. At the time of writing, only the viewing figures for the first six episodes of Doctor Who Series 11 are available. The four-screen estimate is used.

I published the data set online, and used an online R console to create the graphs.

This blog looks at the use of statistics in Britain and beyond. It is written by RSS Statistical Ambassador and Chartered Statistician @anthonybmasters.