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Sampling methods; - Coggle Diagram
Sampling methods;
Random sampling;
This method gives every member of the target group an equal chance of being selected for the sample (eg; by assigning a number to each member and then selecting from the pool at using a random number generator).
Strengths; It is widely accepted that since each member has the same probability of being selected, there is a reasonable chance of achieving a representative sample.
Weaknesses; Small minority groups within your target group may distort results, even with a random sampling technique. It can be impractical (or not possible) to use a completely random technique, eg; the target group may be too large to assign numbers to.
Systematic sampling;
A systematic sampling method is chosen for selecting from a target group eg; every 4th person in a list could be used in the sample. It differs from random sampling in that it does not give an equal chance of selection to each individual in the target group.
Strengths; Assuming the list order has been randomised, this method offers and unbiased chance of gaining a representative sample.
Weaknesses; If the list has been assembled in any other way, bias may be present. For example, if every 4th person in the list was male, you would have only males in your sample.
Stratified sampling;
Here the sampler divides or 'stratifies' the target group into sections, each showing key characteristics which would be present in the final sample. Then each of those sections is sampled individually. The sample thus created should contain members from each key characteristic in a proportion representative of the target population.
eg; If in you target population you have 4/10 women and 6/10 men, then your target population should be representative. If you chose 5 people, you would need to have 2 women and 3 men. Strength = Representative the target population. Weakness = Difficult to carry out (eg; doing the maths).
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Weaknesses; It takes more time and resources to plan. Care must be taken to ensure each key characteristic present in the population is selected across strata, otherwise this design will be a biased sample.
Opportunity sampling;
Participants who are both accessible and willing to take part are targeted eg; employees from a conveniently located employer near the laboratory could be selected from the sample group.
eg; people who walk past you on the street. Strength = Easy, no time wasted waiting for applicants to reply to adverts etc. Weakness = Biased sample, eg; the people that say yes are more likely to be extroverted, meaning an all extroverted sample isn't representative of the wider population as a whole.
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Weaknesses; The consequent sample may not be representative as it could be subject to bias (eg; the conveniently located employer may undertake a selection process for job applicants, making it likely that employees possess certain similar characteristics that are unrepresentative of the wider target group).
Volunteer sampling;
Here the sample consists of people who have volunteered to be in the study (by responding to adverts, usually with a prize available for applying).
Strengths; This often achieves a large sample size through reaching a wide audience, for example with online adverts.
Weaknesses = Those who respond to the call for volunteers may all display similar characteristics (such as being more trusting or cooperative than those who did not apply) thus increasing the chances of yielding an unrepresentative sample.