Editing Internal validity (section)

{{Short description|Extent to which a piece of evidence supports a claim about cause and effect}}
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'''Internal validity''' is the extent to which a piece of evidence supports a claim about [[causality|cause and effect]], within the context of a particular study. It is one of the most important properties of scientific studies and is an important concept in reasoning about [[evidence]] more generally. Internal validity is determined by how well a study can rule out alternative explanations for its findings (usually, sources of [[systematic error]] or 'bias'). It contrasts with [[external validity]], the extent to which results can justify conclusions about other contexts (that is, the extent to which results can be [[generalization|generalized]]). Both internal and external validity can be described using qualitative or quantitative forms of [[causal notation]].