Experiment

What is an experiment?

A manipulation of a variable to test a hypothesis and determine a cause-and-effect relationship

Independent Variable

the variable being manipulated

Dependent Variable

a measured response due to the manipulation of a variable

Controlled variable

variables that are kept consistent in order to avoid influencing the relationship between the IV and the DV

Control Group

participants who are not subjected to the independent variable. They may recieve a placebo

Placebo

a “fake treatment” used in experiments to make sure improvements are not just in someone’s head

Experimental Group

group of participants who are subjected to the independent variable

Standardized Procedure

idea that instructions given to participants are the exact same in both the experimental and control group. Most basic form of control in a study.

Random Allocation

process of assigning participants to either the experimental or control group at random so they have an equal chance of being in either group. Avoids sampling bias.

Question to identify the type of experiment

How was the IV manipulated? How were the participants allocated?

Types of experiments

True and Quasi

True experiment

IV is manipulated by the researcher and the DV is measured under controlled condition. Participants are randomly allocated to conditions.

Example of a True experiment

A group of HS students have to recall words from a list of 16 in a quiet room and another group has to recall words from a list of 16 when listening to One Direction

Quasi experiment

No IV is manipulated and participants are not randomly allocated. Their traits set them apart (fish seller, hotdog vendor, jeweler)

Lab experiment

experiment completed in a highly controlled enviroment

Field experiment

experiment completed in a less controlled environment; the “real world”

A hypothesis should always include…

Operationalized IV, Operationalized DV, Identification of population being studied

Operationalized

clear and specific description of how a variable will be observed or measured in a study

Example of a Hypothesis

HS students will recall more words from a list of 16 words in a quiet room than when a listening to One Direction

Null Hypothesis

must state that there will be NO significant relationship between the 2 variable being studies

Example of Null Hypothesis

Listening to 1D will have no significant effect on HS student ability to recall words from a list of 16

Research Hypothesis

predict there will be a difference between the two conditions

Independent Samples Design

a between subject design; you split your sample between the control group and the experimental group

Repeated Measures Design

a within subjects design; you will use the same sample for both your control and experimental group

Internal vs External validity

Both are important for research to support a theory. Is the reason why its important to perform multiple studies before drawing a conculsion about human behavior

Internal validity

extent to which a study can confidently demonstrate a couse-and-effect relationships b/w the IV and DV without being interfered by confounding variables or bias

External validity

extent to which a study can be gerneralized beyond specific conditions of the experiment

Forms of external validity

People, time, setting

confounding variable

variables that the researcher should’ve controlled but didn’t

Participant Bias

any systematic way that participants expectations motivations or behaviors influence the outcome of a study independently of the variable being tested

Examples of Participant Bias

demand characteristics, social desirability bias, reactivity, and placebo effects

Demand characteristics

cues in the experiment that lead participants to guess the purpose of the study or what the experimenter expects and then changes their behavior accordingly

Demand characteristics: expectancy effect

the participant does what they think the researcher wants

Demand characteristics: screw you effect

the participants decide to do the opposite of what the researcher wants

Reactivity

occurs when participants alter their behavior because they are aware they are being observed or measured regardless of what the study is about

Example of reactivity

a person exercised with greater effort when they know a trainer is watching them

Placebo Effect

occurs when a participant experiences a real change in symptoms or behavior because they believe they are reacting to treatment

Nocebo Effect

occurs when a participant experiences negative effects caused by the belief that something will harm them

Social Desirability Bias

when participants alter their responses or behavior in order to be viewed as more favorable by others; happens when data is self-reported

Carryover effects

occurs in a repeated design; when the effects of one condition influence performance in a later condition

Types of Carryover effects

• interference

• practice

• fatigue

Carryover effects:Interference

when information from the first condition interferes with information from the second condition. Often in happens in memory research.

Carryover effects: practice

refers to the improvement in performance on a task or test that results simply from repeated exposure; can take place due to reduced anxiety as a result of familiarity

Carryover effects: fatigue

decline in performance over time due to tiredness, boredom, lack of motivation, especially when participants are asked to complete long or repetitive tasks