Posted in AP Psychology

Methods and Approaches

Experimental, Correlational, and Clinical Research

An experiment is an investigation seeking to understand relations of cause and effect.

The manipulated variable is called independent variable

The dependent variable is what is measured.

In order to draw conclusions about the result of the controlled experiment, it is important that certain other conditions are met.

The researcher identifies a specific population, or group of interest, to be studied. Because the population may be too large to study effectively, a representative sample of the population may be drawn.

Experimental group: the group receiving to the independent variable.

Control group: the group does not receive the independent variable but should be kept identical in all other respects.

Representativeness is the degree to which a sample reflects the diverse characteristics of the population that is being studied.

Random sampling is a way of ensuring maximum representativeness

Once sampling has been addressed, subjects are randomly assigned into both the experimental and control groups. Random assignment is done to ensure that each group has minimal differences.

Sampling Bias

Bias of Selection

It occurs when people are selected in a physical space.

For example, if you wanted to survey college students on whether or not they like their football team, you could stand on the quad and survey the first 100 people that walk by. However, this is not completely random because people who don’t have class at that time are unlikely to be represented.

Self-selection Bias

It occurs when the people being studied have some control over whether or not to participate.

A participant’s decision to participate may affect the results.

For example, an Internet survey might elicit responses only from people who are highly opinionated and motivated to complete the surveyP

Pre-screening or advertising bias

It occurs often in medial research; how volunteers are screened or where advertising is placed might skew the sample.

For example, if a researcher wanted to prove that a certain treatment helps people to stop smoking, the merce act of advertising for people who “want to quit smoking” might provide only a sample of people who are already highly motivated to quit and might have done so without the treatment.

Healthy user bias

It occurs when the study population tend to be in better shape than the general population

As with the bias of selection from a specific real area, this is an instance in which those subjects might not, in turn, accurately represent their neighborhoods —- even though they gym might have a diverse population.

Researchers use a single- or double-bind design to avoid inadvertently influencing the results.

Single-blind design —-the subjects do not know whether they are in the control or experimental group.

Double-blind design —-neither the subjects nor the researcher knows who is in the two groups.

Double-blind studies are designed so that the experiment does not inadvertently change the responses of the subject, such as by using a different tone of voice with members of the control group than with the experimental group.

In some double-blind experiments, the control group is given a placebo —- a seemingly therapeutic object or procedure , which causes the control group to believe they are in the experimental group but actually contains none of the tested material.

Correlational research —- assessing the degree of of association between two or more variables or characteristics of interest that occur naturally. I

In this type of design, researchers do not directly manipulate variables but rather observe natural-ly occurring difference. 

Correlation does not prove causation; correlation simply shows the strength of the relationship among variables.

  • For example, poor school performance may be correlated with lack of sleep. However, we do not know if lack of sleep caused the poor performance, or if the poor school performance caused the lack of sleep, or if some other unidentified factor influenced them both.

Confounding variable: an unknown factor is playing a role, a third variable, or an extraneous variable.

Through surveys (questionnaires or interviews) —- One way to gather information for correlational studies

Correlational studies can be preferred to experiments because they are less expensive not as time consuming, and easier to conduct.

In addition, some relationships cannot be ethically studied in experiments.

  • For example, you may want to study how child abuse affects self-efficacy in adulthood. But no one will allow yo to randomly assign half of your baby participants to the child abuse condition

Two types of research

Longitudinal studies —- happen over long periods of time with the same subjects (e.g. studying the long-term effects of diet and exercise on heart disease)

Cross-sectional studies —- to test a wide array of subjects from different backgrounds to increase generalizability.

Case studies

They are intensive psychological studies of a single individual.

These studies are conducted under the assumption that an in-depth understanding of single cases will allow for general conclusions about other similar cases.

To investigate the circumstances of the life of notable figures in history.

Researchers must be careful though, because case stud-ies, like correlational ones, cannot lead to conclusions regarding causality. 

Sigmund Freud and Carl Rogers used numerous case studies to draw their conclusions about psychology.

Danger of assessing the outcome of case studies is that the individual studied may be atypical of the larger population.

Therefore, researchers try to ensure that their studies are generalizable —- applicable to similar circumstances because of the predictable outcomes of repeated tests.

Experimental Design

Conceptual definition —- the theory or issue being studied.

Operational definition —- the way in which that theory or issue will be directly observed or measured in the study.

Operational definition have to 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”

—- It is also significant that the study have reliability —- whether or not the same results appear if the experiment is repeated under similar conditions.


本名 谢朋钊, 一个普通的文学爱好者。喜欢继承传统和创新,抛弃老的陋习。


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