PYB210 Lecture Two Notes
Brief Administrative Information
All tutorial material is up on Blackboard.
Tutorials start next week – first tutorial is specifically focused on identifying independent
and dependent variables.
On the first assignment – there are hidden ‘problems’ with the experiment which need to
identified and described. There will also be more than one independent variable.
By the end of this weekend (9 and 10 of March) the IV and DV part of the assignment
should be written.
Remember – the assignment is an essay not a lab report and therefore it should be
structured as such.
Should also be in APA style. Subheading such as IV, DV, control measures etc. could be useful
Keep the introduction brief; do not go into detail about the experiment itself. Simply stating
‘the aim of this essay is to critically assess the design of this experiment’ will suffice.
A good essay always has a conclusion to bring it together. For the purpose of this essay, the
last question about internal validity will essentially serve as the conclusion in which you
bring together everything you have said about the IVs, DVs, extraneous variables etc. and
draw a conclusion as to whether or not the experiment is internally valid.
When giving descriptions of the variables, show your understanding of the terminology in
Often essays such as this make it hard for referencing. The most common areas in which
referencing will be used are when discussing extraneous variables and methods of control.
For example, if a problem is found, you could say ‘problem X was encountered, a method of
dealing with this is Y, as described by Z’.
When using references, remember that while definition references are okay, they do not
augment the answer well and therefore are of little value. Aim for around four to five useful
references which support the statements made.
The Experimental Method
In an experiment, we manipulate something that we think is a causal factor – i.e. something
that we think will cause people’s behaviour to differ. We call this an independent variable.
We then measure the consequence of this manipulation on the behaviour of a person,
which we call a dependent variable.
Therefore, the basic aim of an experiment is to determine whether the independent variable
has the cause or effect which we think it will have.
Independent Variables 101
As previously mentioned, the independent variable is that which your hypothesis predicts to
be a cause of the phenomena you are interested in.
By definition, a variable must be able to vary. That is, have different levels or states.
o For example, the term female cannot be an independent variable because it does not vary,
but gender can.
Every experiment must utilise at least two different states of the independent variable in
order to be able to make a comparison between the two.
o For example, in Doug’s computer anxiety scenario, the experiment would not have worked if
there were only negative-attitude instructors and not positive-attitude instructors with
which to compare.
There are a number of levels to independent variables and it is our job when conducting an
experiment to decide which of these levels we will use. o For example, in Doug’s computer anxiety scenario, the attitude of the instructors (IV) could
have been apathetic or neutral as well as positive and negative, however only the latter two
were chosen for the purpose of the experiment.
Often our hypothesis will direct us as to the number of levels of the independent variable
that will be needed to conduct the experiment.
o For example, in Doug’s computer anxiety scenario, the hypothesis was whether there was a
difference in effect on the participants with either a positive or negative attitude instructor.
Hence, the answer of what levels to include is provided.
Step One: First, you should fully describe the independent and dependent variables and critically
assess their operationalisation.
The first thing to do on the assignment in terms of independent variables is to find where
the prediction or hypothesis is made. This will tell you what the experimenter thinks the
cause will be and should give a good idea of the levels of independent variable the
experimenter should be using.
Then you need to describe the independent variable in terms of everything that will be
covered in the next half hour of lecture.
First – what type of variation is in the independent variable? There are a few different kinds:
o Presence vs. absence – e.g. the effects of a treatment on a patient vs. no treatment on the
o Level of presentation – e.g. the different quantitave font sizes of text on a screen and their
effect on reading ability. A common question here is just how many levels to use?
Theoretically there could be unlimited levels, but this is not practical. The key here is to
examine the literature on the phenomena you are interested in. Presumably there will be
past texts written on the font sizes used previously, and this will act as a guide for where to
o Classification – this is essentially the qualitative equivalent of levels of presentation. Instead
of numbers, we have classifications for the independent variable e.g. boy/girl, positive
attitude/negative attitude etc. Again there could be a potentially unlimited number of
classifications, so it helps to look at what exactly is being examined in order to determine
which classifications to include. For example, in an experiment looking at the effects of
nationality on World War II, it would be impractical to include every nation on Earth. Instead,