= data collected from observation or experiment... doesn't reply on argument or beliefs so open to public scrutiny.
- belief that all knowledge should be devised from sensory experince.
- Objectivity.. without bias.. greatest control
= any component reseacher can replicate the specific study to achieve the same results
- It strenghens the theory, methods and results
- adds confidence
- confirms validity so able to generalise
= ability of reseacher to make a justified extension of their conclusions, apply them to other memebers of the target population and other situations
- it validitates theory to find general principles that can apply to all
- cant always generalise and different cultures, sample used (volunteer, or opportunity)