population and sample -sampling techniques

sampling techniques

opportunity sample

the sample is produced by selecting people who are most easily available at the time of the study

opportunity sample - how

ask random people walking past you in your class

opportunity sample strengths

easiest technique since you just use the first pps you can find

opportunity sample weakness

inevitbly biased since the sample is drawn from a small part of the target population

random sampling

the sample is produced by using a random technique this means each member of the target population has an equal chance of being selected

random sampling - how

place all the names of the target population in a hat and draw out names unil you have your sample

random sampling strengths

unbiased as all members of the target population have an equal chance of selection however not all pps that are selected will aggress to participate so may end up being biased

random sampling -weaknesses

takes more time and effort than other methods since you need to gather a list of all your target population then select them at random, then contact them to see if they will take part

self-selected sampling

the sample is collected by asking for volunteers

self-selected sampling - how

adverise in the local new paper

self-selected sampling strengths

• a way to find wiling pps - researchers need committed pps for time consuming exps

• pps are less likely to drop out since they are interested in the study and applied to do it.

self-selected sampling weaknesses

sample is biased due to if they volunteered they are going to be highly motivated and may even have extra time of there hands and more interested in the study so may no represent the rest of the target population.

snowball sampling

the sample is produced using referrals from intal pps to generate more pps

snowball sampling - how

current pps recruit snowball sampling rit further pps from people they know thus the sample appears to grow like a snowball

snowball sampling strengths

enables a researchers to locate groups of people who are difficult to access to e.d drug addicts. and you only need to reciut ne person and they can do the rest.

snowball sampling weaknesses.

the sample is not likely to be a good cross section of the population because it is made up of friends of friends