Digital video recorders don’t reduce the (possibly zero) effect of ads.
For years, digital video recorders like TiVo, which give viewers the option to skip commercials, have had television advertisers worried. But a study … rebuts the conventional wisdom that the recorders (DVRs) dampen sales. … Matching … each household’s shopping history one year before and two years after the TiVo’s arrival, the researchers found no effect on the purchase of advertised brands, even among those who used DVRs the most. (UofC Magazine Jan’11p25; the study)
Remember: the usual empirical result when people study “how does A influence B” is “no effect.”
As to the question of whether advertising has any effect, I find very interesting the comments by Steve Sailer on this thread and especially the follow-up.
People do large controlled experiments with advertising, but the information is proprietary. It is not clear who has good information. He often describes Proctor & Gamble as at the vanguard of this, sometimes with the implication that no one else followed them. But other times, as where he says that these studies "were likely one factor in the recession that his TV advertising in the otherwise prosperous mid-late 1980s," suggests that the information quickly became widespread. Indeed, wikipedia says that this firm is now employed by 95% of the Fortune 500 CPG, which suggests that they should be showing much more effective ads than 30 years ago. I suspect that it's an empty ritual to be scientific, but they don't actually think about the results.
This isn't particularly shocking. I've always assumed television advertising to be the least effective kind anyway. People have been "skipping" ads for decades - either by changing the channel in an increasingly diverse cable landscape or just getting up and leaving the room for a few minutes until the commercials are over. TV executives have been scamming advertisers for years...