An introduction to Research in psychology - Causal Research

1. Experiments on causal relationships investigate the effect of one or more variables on one or more outcome variables. This type of research also determines if one variable causes another variable to occur or change. In order to do this, experiments should be carried out under highly controlled conditions.

A piece of Causal Research:

Loftus and Palmer (1974) The effects of leading questions
Here, Loftus is suggesting that Leading Questions actually cause people's memories to be distorted.

For further information: http://www.simplypsychology.org/loftus-palmer.html