Causal Comparative or Ex Post Facto Research Design: This research design attempts to explore cause and affect relationships where causes already exist and cannot be manipulated. It uses what already exists and looks backward to explain why.

Experimental Research Design: This design is most appropriate in controlled settings such as laboratories. The design assumes random assignment of subjects and random assignment to groups. It attempts to explore cause and affect relationships where causes can be manipulated to produce different kinds of effects. Because of the requirement of random assignment, this design can be difficult to execute in the real world (non-laboratory) setting.

The differences in causal-comparison and experimental studies are:
CCS: individuals are not randomly selected but selected because they belong to groups
ES: individuals are randomly selected and assigned to two (or more) groups
CCS: the researcher cannot manipulate the independent variable
ES: the researcher manipulates the independent variable
CCS: the independent variable has already occurred and cannot be manipulated
ES: the researcher manipulates the independent variable to determine its effects
CCS: the random sample is selected from two already-existing populations
ES: the random sample is selected from a single population

* * *

Sources:
http://www83.homepage.villanova.edu/richard.jacobs/EDU%208603/lessons/causal.ppt
http://www.dissertation-statistics.com/research-designs.html