The validity of digital trends

At ECIG, Jean-François Trinquecoste asked whether digital trends were valid proxies for public opinion. The argument is that the blogger population is probably not a representative cross-section of the public at large. Good point. As I wrote earlier, this question is one of those I want to look at in the near future.

For now:

1) Digital trends are apparently good predictors of end-point behaviors. Swammer, who provided the data for my analysis, has a blurb here showing that their visibility index outperformed most conventional opinion polls on the French presidential race.

2) But as we look at the series over time, it is clear that visibility scores computed by Swammer differ from opinion polls. See for instance this site where Le Monde, a French Daily, charts opinion polls over time. Whereas opinion polls showed a relatively stable public opinion (Royal and Sarkozy being neck and neck, with "maybe" a slight drop in support to Royal over time, depending on which surveys you look at), visibility scores tell a different story.

Data on IFOP polls as provided by Le Monde look like this:

Visibility scores as provided by Swammer look like this:

Both charts look rather similar, but they tell an entirely different story -- opinion polls suggest that Sarkozy has gathered momentum during the campaign whereas visibility scores suggest just the opposite.

If we look at absolute visibility scores over time, the story takes a new meaning as we watch both candidates becoming more and more visible in the digital sphere, both achieving important absolute gains dwarfing relative differences. 

Now, what can we make out of this?

1) Digital trends could converge towards electoral behaviors merely because uncertainty diminishes i.e. trends would be meaningless random walks, but this is unlikely given the signal to noise ratio. (if digital trends were to randomly approach true behavior over time as uncertainty over the outcome melts away, we would observe diminishing variance around the outcome rather than convergence from a distant initial value.)

2) A more involved question is whether digital trends are a cause of an effect? My implicit assumption was that the digital sphere captures public opinion. But it might be argued that the process works the other way around - public opinion is shaped by influencers operating inside the digital sphere.

The digital-creates-opinions interpretation could be supported by two lines of argument. First, it is a natural extension of the dominant view on the relationship that exists between mass media and public opinion. Second it could rely on the widely held view that the digital sphere is largely the work of a social elite (influencers).

The opinion-creates-digital view would argue that blogs are the direct, unmediated expression of public opinion. And even admitting that the digital sphere is the work of a social elite, it could well be that this work obeys the universal law of supply and demand. Bloggers (and mass media) want readers and will therefore write what the market wants to hear.

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I wish to raise these questions in light of a suggestion that was made to correlate digital trends with the results of tracking opinion polls. As we can argue (convincingly?) on both sides of the causal relationship, correlations will not be useful indicators as they will not answer the validity question. We'll have to construct structural models to separate the (potential) effect that opinion polls have on blogs and vice-versa. What we have learned so far is that opinion polls and digital trends are not interchangeable measures. How they interact and how they capture actual opinions / intentions / behaviors remain open questions.

Thanks to Jean François for vehemently raising questions, and to Philippe Reynet for finding opinion polls data literally within minutes.