sampling methods

• random: every member of target population has an equal chance of getting selected. can be done by pulling names from a hat.
• systematic: every nth person of the target population is chosen.
• stratified: subgroups within a population are identified, p's are obtained from each layer in proportion to their occurrence within the populatio.
• opportunity: selecting anyone who is available and is willing to partake in the study at the time.
• volunteer: participants are self-selecting to partake in a study by either volunteering when asked or by responding to an advert.