Observational studies and experiments

The method of data collection has a major influence on whether a relationship can be interpreted as causal.

In observational studies, there is usually the potential for a lurking variable to underlie any observed relationship, making it difficult to interpret.

The most important characteristic of experiments is that they often do allow relationships to be interpreted as causal ones.

In a well designed experiment, there is little chance of lurking variables driving the observed relationships, so any relationship will be causal.

In a badly designed experiment however, lurking variables can still cause difficulties in interpreting relationships.

Irrigation and wheat growth