Pt. 2 Correlation & Experiment

Experimental Methodology

a system of scientific investigation, usually based on a design to be carried out under controlled conditions, that is intended to test a hypothesis and establish a causal relationship between independent and dependent variables

Non-Experimental Methodology

research methods where researchers do not actively manipulate variables, instead observing and analyzing existing phenomena as they occur naturally (i.e., correlational studies, observational research, descriptive studies, qualitative research, cross-sectional studies, and longitudinal studies, where the focus is on identifying relationships between variables without direct intervention)

Correlation

an orderly relationship between two events, measures or variables

Correlation Coefficient

represents the strength of a correlation; ranges from -1 to +1, where -1 is a perfect negative correlation and +1 is a perfect positive correlation

Positive Correlation

a relationship between two variables in which both rise and fall together (i.e., study hours and test performance); called a direct correlation

Negative Correlation

a relationship between two variables in which the value of one variable increases as the value of the other decreases (babies crying and being held, the discovery that those who are held more tend to cry less); called inverse correlation

Variable

a condition in an experiment or a characteristic of an entity, person, or object that can take on different categories, levels, or values and that can be quantified (measured)

Directionality problem

in correlational research, the situation in which it is known that two variables are related although it is not known which is the cause and which is the effect

IIlusory Correlation

the appearance of a relationship that does not really exist (Ex. left handed people tend to be creative)

Scatter plot

graphs pairs of values; one the y-axis and one on the x-axis

Regression toward the mean

the tendency for extremely high or extremely low scores to become more moderate (i.e., closer to the mean) upon retesting over time

Experiment

a series of observations conducted under controlled conditions to study a relationship with the purpose of drawing causal inferences about that relationship; involves the manipulation of an independent variable, the measurement of a dependent variable

Independent variable

in an experiment, the condition being investigated as a possible cause of some change in behavior. The values that this variable takes are chosen by the experimenter.

Dependent variable

in an experiment, the condition (usually a behavior) that is affected by the independent variable

Control Group

the group of subjects exposed to all experimental conditions or variables except the independent variable

Experimental group

the group of subjects exposed to the independent variable or experimental condition

Random assignment

each participant has an equal chance of being placed into any group

Single Blind

subjects do not know which study group they are in (whether they are taking the experimental drug or a placebo)

Double blind procedure

when neither the participants nor the researcher are able to affect the outcome of the research; usually when the researcher has someone blind to the participants' condition interact with the participants

Placebo

inert substance, such as a sugar pill, that is often administered as a control

Placebo Effect

changes in bx due to participant's expectations that a drug or other treatment will have some effect

Placebo Group

group in research that receives the placebo

Confounding variables

any differences between the experimental and control groups that might affect the dependent variable

Third variable problem

a situation where a seemingly correlated relationship between two variables is actually influenced by a third, unaccounted for variable, leading to a misleading interpretation of causation

Validity

when research measures what the researcher set out to measure; it is accurate

Reliability

when research can be replicated; it is consistent