Experiments
Experiments are the favoured way of collecting data in Psychology.
Experiments have 4 key characteristics
1. They require the manipulation of an independent variable by breaking it into conditions
2. They require the measurement of a dependent variable to observe whether there is any
difference in the measurement as a result of the condition of the IV.
3. They involvement the management of extraneous variables to help ensure that it is the IV
causing a change in the DV not something else.
4. They involve collecting data from a large representative sample of the population.
These 4 characteristics enable 2 goals to be met.
1. A cause and effect relationship between the IV and DV can be established
2. The findings of the experiment can be transferred to a large proportion of the population.
TASK 1
Construct a mind map of experiments. Ensure the 6 points above are included and add any other
details you can.
Sampling
A sample is a group of people taken from the population.
A target population is all the people of interest to a study. For example, if Ms Cody wanted to do
some research about learning at GGS, then target population would be all students of GGS.
In Psychology we can have very large target populations – eg all adults with anxiety or smaller target
populations – eg all competitive athletes over the age of 100.
A good sample always represents the target population it was drawn from. This is so that the
findings can be transferred back to the population.
Transfer
There are 3 major sampling types in VCE Psychology.
Sampling
Technique
Description
How would you
do it
Convenience
(opportunity)
sampling
Selecting the
people who are
accessible and
available at the
time
Asking people at
the local shops
to participate
Giving every
member of the
target population
an equal chance
of being selected
for the sample
Random
Sampling
Stratified
Sampling
Dividing the target
population into
important
subcategories and
selecting sample
members in
proportion to
population.
Strengths
Weaknesses
Saves a lot of
time and money
Unlikely to result
in a
representative
sample
Getting the
name of every
single member
of the target
population and
drawing names
from a hat.
For very large
samples you are
likely to obtain a
highly
representative
sample
For large
populations is
incredibly
difficult and time
consuming to
obtain the names
of every
member.
Dividing the
student body
into year groups
and choosing
the correct
percentage of
each year group
Ensure the
important
characteristics
are represented
in the sample
Time consuming
to identify
categories and
their proportions
TASK 2
Answer the following questions
1. Which type of sampling do you think is the best and why?
2. Which type of sampling do you think is used most often in Psychological research and why?
3. Which type of sampling would you use if you were conducting a study in which GGS students were the
target population? Why?
Is my sample representative?
You have each been given a small bag of M&Ms. This is your sample.
TASK 3
You need to decide if your sample is representative of the M&Ms target population.
The proportion of colours in the M&M target population
Blue
Brown
Green
Orange
Red
Yellow
19%
14%
19%
20%
14%
14%
Is your sample representative?
What do you think you would find if you got a larger sample?
TASK 4
In groups of four, create a stratified sample from your M & M
STEP ONE- List the population
How many people does your population consist of?
STEP TWO- List the population according to the chosen stratification
What proportion (percentage) of each colour is represented in the sample?
For example- if your population is 100 and you have 10 red. The proportion of red people within
your population is 10%
Percentage of RedPercentage of GreenPercentage of Yellow
Percentage of BrownPercentage of BluePercentage of Orange-
STEP THREE- Choose your sample size
You need to achieve a sample size 20, which needs to reflect your population which consists of ____
STEP FOUR- Calculate a proportionate stratification
Above you have calculated the proportion of each colour which is represented within your
population. Now your sample needs to represent these exact proportions but within the smaller
representative sample.
For example, if your population is 1000 and 60% of your population is red, your sample of 100 would
need to have 60 red people.
How we calculate thisDivide sample of 100 by 0.60 (i.e., 0.60 = 60% of the population are red), which gives us a total of 60
red people.
Do the same for all strata within your sample.
**Your Sample is 20 M & M don’t forget**
Number of Red=
Number of Green=
Number of Yellow=
Number of Brown =
Number of Blue=
Number of Orange =