Lesson 1 | Design, Threats to internal and external Validity

Design

It refers to an overall strategy that a researcher
uses to logically and coherently integrate the
various components of a study.

Sampling

is a process through which a researchers selects
portion or segment from the population at the
center of the researchers' study.

Instrument

tools used to gather data for a particular research
topic.

Internal Validity

changes in the dependendent variable can be attributed to the independent variable

External Validity

changes in the dependent variable can be attributed to the extraneous variable

Threats to Internal Validity

• Selection Bias

• Maturation

• History

• Instrumentation change

• Mortality

• Testing

Selection Bias

This results when the subjects or respondents of the study are not randomly selected.

The researcher assigns the students from the higher section to be in the experimental group and the students in the lower section to be in the control group. Obviously, the students in the higher section will perform better.

Maturation

This happens when the experiment is conducted
beyond a longer period of time during which most of the subjects undergo physical, emotional, and/or psychological changes.

History

this refers to a threat to internal validity which
happens during the conduct of the study when an unusual event affects the result of an experiment.

Instrumentation change

The instrument used in gathering the data must not be changed or replaced during the conduct of the study. The instrument must also be applied to all respondents or subjects.

Mortality

There is a threat to validity when one or more subjects die; drop out, or transfer as in the case of a student who has not completed his or her participation in the experiment.

Testing

• may occur in a study when a pretest is given to subjects who have knowledge of baseline data.

• influence of the pretest or knowledge of baseline data on the posttest scores.

Threats to external Validity

• Experimenter effect

• Hawthorne effect

• Measurement effect

Experimenter effect

This threat appears when the characteristics of the researcher affect the behavior of the subjects or respondents.

Hawthorne effect

This occurs when the respondents or subjects
respond artificially to the treatment because they
know they are being observed as part of a research study.

Measurement effect

• It is also called the reactive effects of the pretest.

• It occurs when subjects have been exposed to the treatment through taking the pretest. This exposure might
  affect the posttest results.

• If there is a prior announcement of the conduct of the study, the subjects might prepare, and this will give a superficial result.