# AP Psychology: Experimental, Correlational, and Clinical Research

Experiment

an investigation seeking to understand the relations between cause and effect.

Independent Variable

the variable that is manipulated/changed

Dependent Variable

measured based on the change in the independent variable

Experimental group

the group receiving or reacting to the independent variable

control group

does not receive the independent variable but should be kept identical in all other respects, allows for comparison.

representative sample

a sample of a population that reflects the diverse qualities of that population. Makes studies more easy to conduct.

Random Sampling

a way of ensuring maximum representativeness

Random assignment

after a sample is chosen, subjects are randomly assigned to both the experimental and control groups. It is done to ensure that the two groups have minimal differences

Single-blind design

the subjects do not know whether they ar in the control or experimental group.

Double-blind

the subject nor the researcher knows who is in the two groups. Designed so that the experimenter does not inadvertently change the responses of the subject. (different tone of voice used etc.)

Placebo

a seemingly therapeutic or procedure that causes the control group to believe they are in the experimental group but actually contains none of the tested material.

Correlational Research

involves assessing the degree of association between two or more variables or characteristics of interest that occur naturally. This type of research does not directly manipulate variables but rather observes naturally occurring differences.

Correlation…

does not prove causation

counfounding (3rd variable)

an unknown third factor that is playing a role in the problem.

Clinical research

often takes the form of case studies

Case Studies

intensive psychological studies of a single individual. Conducted under the assumption that in-depth understanding of a single case will allow for general conclusions about other similar ones.

Generalizable

applicable to similar circumstances because of the predictable outcomes of repeated tests.

Developmental Psychology

Two important research methods associated with it are longitudinal and cross-sectional

Conceptual Definition

the theory or issue being studied

operational definition

how a theory or issue will be directly observed or measure in the study. Must be internally and externally valid.

Internal Validity

the certainty with which the results of an experiment can be attributed to the manipulation of the independent variable rather than to some other, confounding variable.

External Validity

the extent to which the findings of a study can be generalized to other contexts in the ‘real world.”

Reliability

whether or not the same results appear if the experiment is repeated under similar conditions.

Descriptive Statistics

Summarize data: central tendency, mean, mode, median, normal curve, variability, standard deviation, percentile, correlational coefficient, Pearson correlational coefficient, positive correlation and negative correlation.

inferential statistics

allow researchers to test hypotheses about data and to determine how confident they can be in their inferences about the data.

Central Tendency (descriptive)

characterization of the typical value in a set of data.

Mean (descriptive)

arithmetic average of a set of numbers.

mode (descriptive)

most frequently occurring value in the data set

median (descriptive)

number that falls exactly in the middle of the distribution of numbers

normal curve (bell curve/descriptive)

represents the mean, median, and mode in a graph. Mean is the location of the center of the graph. Standard deviation determines the height and width of the graph. Standard deviation is large then it is short and wide, if it is low, the curve is tall and narrow.

Skewed normal curve (descriptive)

the median is a better indicator of central tendency than the mean.

negative skew (descriptive)

more exceptionally small values than exceptionally large values.

positive skew (descriptive)

more exceptionally large values than exceptionally small values.

Variability (descriptive)

refers to how much the numbers in the set differ from each other.

Standard deviation (descriptive)

measures a function of the average dispersion of numbers around the mean and is a commonly used measure of variability.

percentile (descriptive)

used frequently when reporting scores on standardized tests. They express the standing of one score relative to all other scores in a set of data.

correlational coefficient (descriptive)

describes how attributes being studied relate to one another. numberical value that indicates the degree and direction of the relationship between two variables. they range from +1.00 to -1.00.

Pearson correlational coefficient (descriptive)

describes the linear relationship between two attributes. They can be positive, zero, or negative. 1 is perfect correlation, -1 is perfect negative correlation, and zero indicates the attributes are not related.

generalize (inferential)

make sure the results are applicable to a large, diverse group of people.

sample (inferential)

a representative group of a large population

population (inferential)

the large group to whom the psychologist is trying to generalize

representative

if the sample reflects the characteristics of the population as a whole it is considered representative.

null hypothesis (inferential)

states that a treatment had no effect in an experiment

alternative (inferential)

states that the treatment did have an effect in an experiment

alpha (inferential)

the accepted probability that the result of an experiment can be attributed to chance rather than the manipulation of the independent variable. It is set at .05 which means that an experiments results will be considered statistically significant if the probability of the results happening by chance is less than five percent.

Type 1 Error (inferential)

refers to the conclusions that a difference exists when in fact this difference does not exist.

Type 2 error (inferential)

refers to the conclusion that there is no difference when in fact there is a difference.

p-value (inferential)

the probability of making a type 1 error. A p-value indicates that the results are statistically significant (not due to chance). If p=.05 there is only a 5 percent chance of making a type I error. In other words, a difference as extreme as what was obtained would be found only 5 percent of the time if the null hypotheses were correct.

informed consent

participants in psychological studies can only participate in the study after they have been told what their participation entails.

debriefing

after participation, participants must be told the exact purpose of their participation in the research and of any deception that may have been used in the process of the experimentation.

Applied Psychology

psychology that is put directly into practice.

Basic Psychology

grounded in research and is often conducted at universities and private laboratories.

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