Sampling is selecting individuals from a population. Target population - rarely available. Accessible Population - the realistic group that is available. Random sampling vs. non random sampling non-random sampling - almost always leads to bias.
Bias in research - steers things towards one direction or another
simplified random sampling - just random Stratified random sampling - subgroups then random Cluster random sample - use the group as the sampling unit rather than individuals. (using a school, rather than individuals) Systematic sample - choosing every nth individual Convenience sample - population that is available purposive sample - special qualifications of the people to be in your sample. (Thirlby did this)
How many? Using stat methods, you need at least 30 for experimental, 50 for correlational, 100 for a descriptive
Qualitative studies 1-20
Can you generalize to the rest of the population?