• Construct validity- IV reflects hypothetical construct
• Content validity- operationalised to reflect variable of interest
• External validity- can be generalized
• Ecological validity- real-life events.

Reduce chance of Type 2 error- missing the relationship.

IV: minimise error variance.

Want to see a change no overlap between conditions

DV: increase sensitivity - can detect small influences

Minimise measurement error- reliable

• Choose variables and conditions carefully- content/construct/external/ecological validity.
• Create strong manipulations- powerful study.
  
• Consistency between/within conditions.
• Use manipulation checks- to check IV worked.
  

Ceiling effect: maximum too low

Floor effect: minimum too high

• Practice effect: skill/boredom after practice- reduce validity.
• Carryover effect: changes in the psychology of pps due to earlier trials, eg. frustration.
• Response set: response strategies- reduce validity.

Prevent order effect.

Systematically changing the order of trials for each pp. in a balanced way.

• Sensitive DV
• Don't restrict ranges of responses
• Practice/multiple trials (reliability)
• Counterbalance or randomise order.