sampling

what is the population of an experiment?

the entire group that you want to draw a conclusion about.

what is the sample of an experiment?

the specific group that you will collect the data from.

what is random sampling?

a sampling technique in which every member of the target population has an equal chance of being selected

how do you conduct a random sample?

1. you would first define your target group and sample size (e.g 10 psychology students from your college class).
2. You could then assign a number to every student in the class and then select 10 participants in an unbiased way.( eg. by using a random number generator on a computer)
3. You could also put the name of every student in to a hat, mix thoroughly, and select 10 names from the hat, again ensuring that this is done in an unbiased way.

what is a strength of random sampling?

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.

what are the issues with random sampling?

the data received from a randomly sampled piece of research could be the result of accidental bias as you can’t ensure that there is equality in: gender equality, age, social class etc.

this then is generalised to the whole population when maybe not everyone is accounted for

what is systematic sampling?

a type of sampling process in which all the members of a population are listed and then some objective, orderly procedure is applied to randomly choose specific cases

what is a strength of systematic sampling?

assuming the list order has been randomised, this method offers an unbiased chance of gaining a representative sample.

what are the issues with systematic sampling?

if the list has been assembled in any other way, bias may be present, eg if every fourth person in the list was male, you would have only males in your sample.

what is stratified sampling?

a sampling technique where the researcher divides or 'stratifies' the target group into sections, each representing a key group (or characteristic) that should 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.

what is a strength of stratified sampling?

it avoids the problem of misrepresentation sometimes caused by purely random sampling

what are the issues with stratified sampling?

it takes more time and resources to plan

care myst be taken to ensure each key characteristic present in the population is selected across strata, otherwise this will design a biased sample

what is opportunity sampling?

participants who are both accessible and willing to take part are targeted, e.g. employees from a conveniently located employer near the laboratory could be selected for the sample group.

what is a strength of opportunity sampling?

it is easy and inexpensive to carry out

what are the issues with opportunity sampling?

the consequent sample may not be representative as it could be subject to bias

(e.g. 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).

what is volunteer sampling?

the sample consists of people who have volunteered to be in the study.

what is a strength of volunteer sampling?

this often achieves a large sample size through reaching a wide audience, eg. with online advertisements

what are the issues with volunteer sampling?

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.