Chapter 9: True experiments
True experiment attempts to establish a cause effect relationship by demonstrating that changes in
one variable are directly responsible for changes in another variable.
Elements of a true experiment
1. Manipulation
◦ The researcher manipulates one variable by changing its value to create a set of two
or more treatment conditions
◦ Manipulation on independent variable
◦ Through manipulation one makes groups / levels
◦ Manipulation of environment:
• Influence of social norms: If you think its ok, and others do it then you can
behave the same way e.g. parking lot in which people prior littered vs clean
parking lot
1. Measurement
◦ Second variable is measured for a group of participants to obtain a set of scores in
each treatment conditions
◦ Scores on dependent variables
• Example of measurement: Either people throw trash on ground or take it with
them
1. Comparison
◦ Scores in different treatment conditions are compared
◦ Consistent differences between treatments prove that manipulation is reason for
changes
◦ Does manipulation effect dependent variables
1. Control
◦ All other variables (confounders) are controlled to make sure they do not influence
the two variables examined
• Example: Change treatment every other hour, randomize order of treatments
• Some things you cannot control: weather, people walking by
Milgram experiment? Not a true experiment
Manipulation? No groups
Measurement? Voltage
Comparison? No
Control? Some but bare
,Mundane Realism
• Extent to which the experimental situation is similar to situations people are likely to
encounter outside of the lab
◦ Milgram experiment: low, shocks coming from authority is very unlikely
Experimental Realism
• Extent to which participants experience the experimental situation as intended
• Extent to which the participants become immersed in the simulation and behave normally,
unmindful of the fact they are in an experiment
◦ Milgram experiment: high, thought they were really giving shocks and obeying
The experimental research strategy
By manipulating the independent variable we create different groups, and the groups receive
different treatments. The different scores of the dependent variable are caused by the treatment,
unless there are extraneous variables
, 3 methods to control extraneous variables
1. Holding a variable constant
• E.g. All individuals in experiment could be observed in the same room, at the same
time of day by the same researcher
1. Matching values across treatment conditions
• Matching levels of the variables across treatment conditions
• E.g. all have same amount male and female: 20f, 10m
1. Control by Randomization
• Disruption of any systematical relation to prevent from becoming confounding
variable
• Using an unpredictable and unbiased procedure to distribute different values e.g.
random assignment of participants
Chapter 1: Scientific method
Approach to acquiring knowledge that involves formulating specific questions and then
systematically finding answers
Scientific method
• Science is empirical: answers are obtained by making observations
• Science is public: replicable
• Science is objective
• Science vs Pseudoscience
◦ Is refutable
◦ Grounded in past theory
◦ Actively test and challenges own theories, adapts theory when new evidence is there
◦ objective and unbiased
1. Find a research idea
- Often based on every day events, informal observation
- Induction: Small set of specific observations form the general basis for forming a general
statement about a larger set of possible observation
- Select general topic, review the literature
True experiment attempts to establish a cause effect relationship by demonstrating that changes in
one variable are directly responsible for changes in another variable.
Elements of a true experiment
1. Manipulation
◦ The researcher manipulates one variable by changing its value to create a set of two
or more treatment conditions
◦ Manipulation on independent variable
◦ Through manipulation one makes groups / levels
◦ Manipulation of environment:
• Influence of social norms: If you think its ok, and others do it then you can
behave the same way e.g. parking lot in which people prior littered vs clean
parking lot
1. Measurement
◦ Second variable is measured for a group of participants to obtain a set of scores in
each treatment conditions
◦ Scores on dependent variables
• Example of measurement: Either people throw trash on ground or take it with
them
1. Comparison
◦ Scores in different treatment conditions are compared
◦ Consistent differences between treatments prove that manipulation is reason for
changes
◦ Does manipulation effect dependent variables
1. Control
◦ All other variables (confounders) are controlled to make sure they do not influence
the two variables examined
• Example: Change treatment every other hour, randomize order of treatments
• Some things you cannot control: weather, people walking by
Milgram experiment? Not a true experiment
Manipulation? No groups
Measurement? Voltage
Comparison? No
Control? Some but bare
,Mundane Realism
• Extent to which the experimental situation is similar to situations people are likely to
encounter outside of the lab
◦ Milgram experiment: low, shocks coming from authority is very unlikely
Experimental Realism
• Extent to which participants experience the experimental situation as intended
• Extent to which the participants become immersed in the simulation and behave normally,
unmindful of the fact they are in an experiment
◦ Milgram experiment: high, thought they were really giving shocks and obeying
The experimental research strategy
By manipulating the independent variable we create different groups, and the groups receive
different treatments. The different scores of the dependent variable are caused by the treatment,
unless there are extraneous variables
, 3 methods to control extraneous variables
1. Holding a variable constant
• E.g. All individuals in experiment could be observed in the same room, at the same
time of day by the same researcher
1. Matching values across treatment conditions
• Matching levels of the variables across treatment conditions
• E.g. all have same amount male and female: 20f, 10m
1. Control by Randomization
• Disruption of any systematical relation to prevent from becoming confounding
variable
• Using an unpredictable and unbiased procedure to distribute different values e.g.
random assignment of participants
Chapter 1: Scientific method
Approach to acquiring knowledge that involves formulating specific questions and then
systematically finding answers
Scientific method
• Science is empirical: answers are obtained by making observations
• Science is public: replicable
• Science is objective
• Science vs Pseudoscience
◦ Is refutable
◦ Grounded in past theory
◦ Actively test and challenges own theories, adapts theory when new evidence is there
◦ objective and unbiased
1. Find a research idea
- Often based on every day events, informal observation
- Induction: Small set of specific observations form the general basis for forming a general
statement about a larger set of possible observation
- Select general topic, review the literature
