After reading this chapter, you should be able to

• Explain the meaning of confounding variables.
• Explain the meaning of statistical conclusion validity, construct validity, internal validity, and external validity and their importance in the research process.
• Identify and explain the types of evidence that are needed to reach a causal conclusion.
• Explain the threats to internal validity and be able to identify when they might exist in a research study.
• Explain the threats to external validity and when they might exist in a research study.
• Explain the role of operationalization of constructs in research.
• Identify and explain the types of validity or trustworthiness used in qualitative research.
• Identify and explain the types of validity or legitimation used in mixed research.