  We check the claims that data from Google Trends contain enough data to
predict future financial index returns. We first discuss the many subtle (and
less subtle) biases that may affect the backtest of a trading strategy,
particularly when based on such data. Expectedly, the choice of keywords is
crucial: by using an industry-grade backtesting system, we verify that random
finance-related keywords do not to contain more exploitable predictive
information than random keywords related to illnesses, classic cars and arcade
games. We however show that other keywords applied on suitable assets yield
robustly profitable strategies, thereby confirming the intuition of Preis et
al. (2013)
