Sampling

When we carry out research we need people to take part, these are called participants. It is important to use suitable participants in your study. Hello!

The population is the group of people from whom the sample is drawn The population is the group of people from whom the sample is drawn. For example if the sample of participants is taken from sixth form colleges in Leeds, the findings of the study can only be applied to that group of people and not all sixth form students in the UK and certainly not all people in the world.

Obviously it is not usually possible to test everyone in the target population so therefore psychologists use sampling techniques to choose people who are representative (typical) of the population as a whole. = If your sample is representative then you can generalise the results of your study to the wider population.

Sampling Techniques We will now examine some of the techniques used by Psychologists to obtain participants for their sample

Opportunity Sampling Common Room Geek! Want to be in my study? Common Room Opportunity sampling is the sampling technique most used by psychology students. It consists of taking the sample from people who are available at the time the study is carried out and fit the criteria you are looking for.

Opportunity Sampling Strengths Weaknesses Participants are chosen because they are convenient. This means that they might have been selected because they have volunteered, because they are in the locality, or because they are known to the researcher. The researcher uses participants that she has the opportunity to use. Strengths Less time-consuming than other techniques because time is not spent planning and using sophisticated systems for selection. Weaknesses Likely to be a biased sample because only certain types of people will volunteer for psychology research If people come from the same locality they may be similar in terms of their characteristics (e.g. all University of Nottingham students) or they may have similar characteristics (e.g. all middle class). The researcher may show bias when choosing the participants whether intentional or not (e.g. know they will behave in a certain way)

Random Sampling This is a sampling technique which is defined as a sample in which every member of the population has an equal chance of being chosen. This involves identifying everyone in the target population and then selecting the number of participants you need in a way that gives everyone in the population an equal chance of being picked.

Random Sampling Strengths Weaknesses Participants are chosen mathematically, using chance. Every member of the sampling frame has an equal chance of being selected. E.g. selected by computer from the electoral roll. Strengths It avoids bias as the researcher has no control over who is selected. The law of probability says that the researcher will normally get a representative sample. Weaknesses It is time-consuming because all potential participants need to be identified before a sample can be drawn. There is a small chance that a ‘freak’ sample may drawn, which would be unrepresentative.

Self-selected Sampling Volunteers needed for psychological study on learning I just love to be helpful…. I’ve always wanted to be in a study…. Sounds rubbish… Gotta do my hair.. Psych Lab Self selected sampling (or volunteer sampling) consists of participants becoming part of a study because they volunteer when asked or in response to an advert.

Volunteer sample This is another way of saying self selected sample. This sampling technique consists of participants becoming part of a study because they volunteer when asked or in response to an advert.   Strengths: This technique, like opportunity sampling, is useful as it is quick and relatively easy to do.  It can also reach a wide variety of participants.  Weaknesses: However, the type of participants who volunteer may not be representative of the target population for a number of reasons.   For example, they may be more obedient, more motivated to take part in studies and so on.

Stratified Sampling = 60% female 40% male = 60% female 40% male Stratified sampling involves classifying the population into categories and then choosing a sample which consists of participants from each category in the same proportions as they are in the population.

Stratified Sampling Work out what groups there are in the population Select participants by taking lots of people who fit into the group, and picking some at random (a sample) Weakness: time consuming Strength: represents the population subgroups

Neither random or systematic sampling James has taken the list of Y10 students as his sampling frame and given every student a number. He then puts all of the numbers into a hat; his ‘sample’ is made up of the people whose number’s he picked out of the hat. Is this: Random sampling Systematic sampling Neither random or systematic sampling a

Judy decides random sampling is the best method for her research Judy decides random sampling is the best method for her research. Which of these describes what she should do? Number her participants and then use the ones a number generator (e.g. on a calculator) comes up with Pick every 10th participant from her sampling frame Put all the participant’s names into a hat and pick out the ones to use A and c are both random sampling A and b are both random sampling d

Saima decides systematic sampling is the best method for her research Saima decides systematic sampling is the best method for her research. Which of these describes what she should do? Take her register (in alphabetical order) and pick every 5th student on it. Take a list of students and number them with numbers 1-10, then pick each number 5 Take her register and assign each student a number then pick numbers out of a hat (or bingo machine, etc.) A and c are both systematic sampling A and b are both systematic sampling e

Booklet Pg. 18-22