  Previous studies of the stock price response to individual trades focused on
single stocks. We empirically investigate the price response of one stock to
the trades of other stocks. How large is the impact of one stock on others and
vice versa? -- This impact of trades on the price change across stocks appears
to be transient instead of permanent. Performing different averages, we
distinguish active and passive responses. The two average responses show
different characteristic dependences on the time lag. The passive response
exhibits a shorter response period with sizeable volatilities, and the active
response a longer period. We also study the response for a given stock with
respect to different sectors and to the whole market. Furthermore, we compare
the self-response with the various cross-responses. The correlation of the
trade signs is a short-memory process for a pair of stocks, but it turns into a
long-memory process when averaged over different pairs of stocks.
