Hulu, the online video site, is serving up more streams but has been serving fewer users, according to Nielsen. Hulu is in the top two or three video sites, but still comes some considerable way behind YouTube, which accounts for over half the video clips viewed online in the United States. There is now some controversy over the actual number of users Hulu has. Hulu prefers to believe comScore figures of over forty million, while others put the figure at less than a quarter of that.

Nielsen estimates that Hulu served 373 million video streams in the United States in April, compared to 348 million in March and 309 million in February. In its VideoCensus for April, Nielsen estimated that Hulu delivered just under 4% of the nearly 9.5 billion online video streams it reported, of which YouTube accounted for nearly 5.5 billion. However, it says that it attracted 7.4 million unique users in April, compared to 9.5 million in February. Hulu says that underestimates the real reach.

Nielsen uses a NetView panel sample of up to 200,000 users to estimate usage, based on sampling techniques traditionally employed to statistically estimate television ratings.

Similar methods are used by comScore, although the comScore panel includes around two million people around the world, with a million of them in the United States.

The comScore Video Metrix report found that Hulu served 380 million video streams in March, which it put at 2.6% of the 14.5 billion online videos viewed in the United States, of which Google sites, including YouTube, accounted for nearly 6 billion. The comScore data puts the number of unique users for Hulu in the United States in March at 41.5 million, with Google sites, including YouTube reaching over 100 million.

While Nielsen and comScore estimate similar numbers of streams for Hulu, the number of unique users differs considerably. Other data points from Quantcast and Compete put the number of visitors to the Hulu site at closer to 14.5 million and 7 million respectively.

In March, Jason Kilar, the chief executive of Hulu referred to comScore figures of over 24 million users in January.

It seems extraordinary that there should be such disagreement over the estimated number of users.

Site owners tend to cite third party statistics to address any scepticism about self-reported figures and to place them in context with competitors.

While panel based samples can provide a reasonable statistical measure of relative performance, the site owner is best placed to provide actual numbers, although even here measurement remains a rather inexact science, which is open to definition and interpretation.

It is ironic that online video should be a very measurable medium, but the industry still needs to establish acceptable methodologies and standards to enable it to be accurately reported.