INTRODUCTION TO EXPERIMENTS
SEMESTER 1, PRACTICALS

MAIN TOPICS FOR CLASS
 What is an experiment?
 What is experimental psychology?
 Control and experimental group
 Variables in an experiment (IV, DV, Extraneous, control and confounding)
 Replication & validity (internal and external) in an experiment

 Experiments have been the mainstay of
psychological research for over 150 years
 First experimental lab:
Leipzig Univ., 1879, Wilhelm Wundt

WHAT IS RESEARCH?
 Research is a systematic, logical process for COLLECTING, ANALYZING, INTERPRETING
information (DATA) in order to INCREASE our UNDERSTANDING of a given phenomenon.
 Research: DISCOVERY & ADVANCEMENT OF HUMAN KNOWLEDGE
 What sets research apart from OTHER WAYS OF KNOWING is the SCIENTIFIC APPROACH.

 One method used in psychological research is EXPERIMENTS.
 Experiments are very useful when we want to establish CAUSE & EFFECT relationships.
 But, what is an experiment? Lets start with an example…..

Lets assume a research question:
 What is the effect of instrumental music on learning?
Learning what?
 A list of words.

STEP 1: SELECT A SAMPLE /SUBJECTS
 N=100 students of 2nd year across different courses of LSR
So all subjects are:
 18-19 years of age
 Female
 Undergraduate

 Step 2: Randomly divide them into 2 groups

Group 1
N=50
Group 2
N=50
Step 3: Data collection
• Each group is given a list of 50 words
• 1 hour to learn the list
Group 1
N=50
Learns the list with music
Group 2
N=50
Learns without music
Both groups are asked
to recall & write the
words
They are given 5
minutes for recall.

IMPORTANT FEATURES OF THE DESIGN
I was interested in the effect of one thing upon another
The groups were randomly created (random selection & random assignment)
Groups have to be same/similar in every respect except music
The groups were relatively large, as is required for statistical analysis

WHAT WERE THE RESULTS OBTAINED?
 Music group performed significant better than non-music group.
 What may I conclude?
 If the groups were similar in every possible way, except 1 (presence of music)…
 Then the difference seen in their performance is most probably due to the factor of music only.

VARIABLE
 Any entity that varies and can be measured
 Height, weight, income, mileage of a car
 In an experiment , a variable may be MANIPULATED, OBSERVED,
CONTROLLED

INDEPENDENT VARIABLE
Systematically manipulated
(altered/varied) by the experimenter to
study its effects
DEPENDENT VARIABLE
The variable which is observed and
measured

EXTRANEOUS VARIABLES
 Any variable the researcher is not interested in and should be prevented from effecting the
outcome of the experiment.
Situational
Any feature of the research situation
which influences the outcome (DV)
apart from the IV
e.g.,
NOISE
TEMPERATURE
TIME OF DAY
INDEPENDENT VARIABLE
Subject related
Characteristics of a subject that may
effect the outcome (DV) of the study
e.g., INTELLIGENCE
MOTIVATION
AGE

CONTROL VARIABLES
 These are variables kept constant across conditions to minimise their effect on the
experiment
Examples:
 Subjects of both groups come for the experiment at the same time of the day
 They study the same list
 Time of learning is same for both groups: One hour
 All subjects are of the same age, gender

CONFOUNDING VARIABLES
 Any extraneous variable that systematically varies with the IV adversely effecting the
researcher’s ability to draw CAUSE & EFFECT relations
 Confound= Cause confusion

ANOTHER EXAMPLE
 AIM: To study the impact of cell phone usage on Driver’s reaction time in an emergency
situation
 IV?
 DV?
 Extraneous variables that need to be controlled

IV
• Talking on cell phone
DV
• RT in emergency situations
Control
• Age of subjects in both groups
• Nature of emergency faced by both groups
• Driving experience of persons in both groups

WHAT ARE EXPERIMENTS?
 Are a method of collecting data…….
 Wherein the experimenter creates a situation in which ……….
 1 set of variables are manipulated (IV) and another set are controlled (control variables)to……..
 Observe a relation of cause and effect between the manipulated variable (IV) and the
observed variable (DV)
It has 3 elements:
• Change in the events that are hypothesized to have an effect – these events are called IV
• Looking for the effect of the change on the system of observation- DV
• Keeping all other conditions constant- Control variables

CRITERIA FOR AN EXPERIMENT
Experiment
1. Manipulation of IV
2. Random
assignment of
subjects
3. Ability to draw
cause and effect
relations
Quasi-experiment
1. Manipulation of IV
2. NO Random
assignment of
subjects
3. NO Ability to draw
cause and effect
relations
Ex post facto study
1. NO Manipulation
of IV
2. NO Random
assignment of
subjects
3. NO Ability to draw
cause and effect
relations

WHAT IS EXPERIMENTAL PSYCHOLOGY?
Experimental psychology is the branch of psychology that deals with designing and carrying
out experiments on behaviour & processes that underlie them.
It is grounded in the experimental method where investigators systematically alter 1 or more
variables, under controlled conditions, to determine whether such changes will influence another
variable,
Sensation, perception, learning, memory are some of the topics commonly studied

Experimental group:
Group that receives treatment or
an active level of the IV
Control group:
Group not exposed to the treatment
It receives a zero level of IV
Purpose of the control group:
To provide a standard of behavior to which
the experimental group can be compared
Experimental and Control Groups

REPLICATION
 Process of repeating a study to determine whether the Original findings can be duplicated
 When the results are duplicated we can feel more confident about our conclusions
 When they do not duplicate it may lead to better research & discoveries as scientist look for
cues to explain why the results of one study what different from the other

INTERNAL VALIDITY
 Represents the degree to which an experiment supports clear causal conclusions.
 If extraneous variables are controlled, we can be confident that the change in DV was caused
by the change in IV (High internal validity)
 However if we are unable to do so, it will have low internal validity as we cannot be show that
the change in in DV was due to the manipulation of the IV

EXTERNAL VALIDITY
 This is concerned with whether the findings of an experiment are applicable to
situations other than the one in which it was conducted
 For example :
Do findings obtained from a given sample generalize to the larger population from which
the sample was selected ?
Do findings of the study conducted in a lab generalized to everyday life ?