This research methods in psychology video is Sampling. When researchers conduct studies,
and then publish findings it's tempting to think the findings apply to all of us. But we need to
think carefully about who exactly took part in the study, and if the behaviour of those participants
can be genralised to everyone. So in this video we will be looking at 5 sampling techniques Random,
Systematic, Stratified, Opportunity and Volunteer. We will of course also consider the strengths and
weaknesses of each. INTRO
Our first definition is for the term target population, this is every individual that forms
part of the group you plan to study. So likely to be a very large number, if you are investigating
pensioners, or four year old children, or sixth form students we won't be able to test all of
them, we need to take some of them, a sample. What we hope to do when we get our results
from the sample, is apply the results back to the target population, this is called generalisation.
However, members of a population vary in many ways, so ideally we want a sample that is
representative of the larger population. Random
So let's start with random sampling, now it's not just grabbing anyone to take part in your study,
it's mathematically random, so everyone in the population has the same chance or
probability to be selected as a member of the sample. A researcher first needs a list
of all members of the population. And then use a method of selecting them randomly. So putting
the names into a hat and drawing them out until they have a full sample, or giving each name a
number and using a random number generator. The strength of this method is it avoids
researcher bias. The researcher can’t just choose the people they want in the study,
which could influence the results. However because it is random,
we could randomly get an unrepresentative sample, maybe not representing all minority groups.
If the population size is large a random sample can be time consuming,
Systematic Systematic sampling is similar to random, we
still need the list of the population, but instead of picking randomly, we go down the list and
choose every 5th or 10th or Nth person. You can imagine a teacher picking a sample from her class
using the register and calling out every 3rd name. This again removes the chance for researcher bias
in picking who they want in their studies. And with a small population studied, and lists of the
population already exist, such as with the register can be a quick way of getting a sample
It's unlikely but still possible to to get an unrepresentative sample using a
systematic approach, and with large populations it's difficult to get a full list of members.
Opportunity An opportunity
sample is the easiest sample to get and most commonly used. The researcher simply includes
anyone in the sample that they can get their hands on by simply asking them to take part.
For that reason many psychology studies are actually conducted on university students.
A strength of this of course is it's a much faster way of getting a sample than
other methods. This could save money and allow the researcher to complete the study faster.
But there are big problems with an opportunity sample. There is the potential for researcher
bias. The researcher decides who to ask and who not to ask, potentially manipulating
the results. Also the sample is likely not representative as the researcher only has
access to a limited section of the population, in most cases, young university students.
Volunteer Another word for a volunteer sample
is a self selecting sample. This makes clearer the important factor of this sampling method,
that the participants select themselves , they volunteer themselves. They are not
directly asked. So they may see an advert in the newspaper or online and put themselves forward.
So a strength of this is by using an advertisement, especially in a popular newspaper,
the researcher can reach a large number of potential participants. And is relatively
easy to collect as after placing the ad, the participants are putting themselves forward.
but we have the issue of volunteer bias, people who volunteer for studies are a
certain type of person. They are of course helpful, and they have the time to take
part in psychology studies. But we want to include people who are unhelpful, and people
who are busy. If we don't we may not be able to generalise our findings to the wider population.
Stratified A stratified sample is the most
complex type of sample, but it tries to avoid some of the problems of the other methods. A stratified
sample creates a sample that is representative of the population as a whole. So firstly the
researcher will identify subgroups, or strata and their proportion in the wider population.
Then the sample is made by randomly selecting participants from within each strata
so they are represented in the same population in the final sample. So if 10% of your population
were university graduates, 10% of your sample would be university graduates.
The big positive of this approach to sampling is the sample is representative of the larger
population, meaning we can be confident in genralising what we find to the population.
Also this sampling method avoids researcher bias as it randomly
selects participants from within each strata. But the researcher does decide what strata are
important to consider, meaning there may be some bias in the selection of strata,
and as you can imagine stratified sampling is time consuming and difficult.
Bouns fact - WEIRD participants So when considering sampling we
need to consider the implications of bias and generalisation. I've already told you
what genralisation is and about researcher bias and volunteer bias. But going a little deeper,
a critisicm of psychology studies is most of them have been completed on WEIRD participants.
And by weird I mean most participants of from a western, educated, industrial,
rich and democratic background. In fact if you are an American university student you are 4000
times more likely to be in a psychology study than a random non westerner. This leads us to
consider if much of what we know about psychology actually applies, or genralises around the world.
Also the samples of historical studies, often ignored or underrepresented women,
leading us to also consider gender bias in much of accepted psychological theory.
Outro So that was Sampling,
I have 6 tutorial videos covering the 2017,18 and 19 AS and A-level research methods sections,
these videos have worked examples to every question and are full of exam tips. Patrons
at the neuron level and above can access these, and many, many more hours of exam tutorial videos,
as well as over a hundred printable resources from across the A-level over on psych boost .com
I do want to thank all the students and teachers who have supported psych boost
over on patreon during the development of the research methods unit. It's their
support that allows me to teach part time so I can make psych boost on youtube for everyone.
So thanks to them, and I will see you all in the next research methods video,
experimental design.