Module 12: Between-Participants Experimental Designs Flashcards
Between-participants design
An experiment in which different participants are assigned to each group. The independent variable needs at least two groups in this experiment, most often a control group and experimental group
Posttest-only control group design
an experimental design in which the dependent variable is measured after the manipulation of the independent variable. Such as with the memory study in which people receive a device. The manipulation in this case in tested after the experiment.
Nonequivalent control group
the control group is nonequivalent, using random sampling and random assignment is sufficient enough to address this problem
History effect
changes in the dependent variable may be due to a historical event (such as corona crisis). Are most likely unrelated to the study but may nonetheless affect the dependent variable.
E.g. stress-reducing program where the posttest is taken during midterm or final exams, may lead to an increase in stress.
Maturation effect
Participants mature physically, socially, and cognitively during the course of the study. Any changes in the dependent variable may be due to maturation and not to the independent variable. The control group helps with this, if they change without the treatment you know there is a maturation effect
Testing effect
Repeated testing within a study may lead to better or worse scores. Although most studies only have pretest and posttest measures, some require more testing. In these cases, participants are exposed to the same or similar tests numerous times. As a result, changes in performance on the test may be due to prior experience with it, not to the independent variable.
- Practice effect
- Fatigue effect
Threats to internal validity
- Nonequivalent control group
- History effect
- Maturation effect
- Testing effect
- Practice effect
- Fatigue effect
- Regression to the mean
- Instrumentation effect
- Mortality
- Diffusion of treatment
- Experimenter effect (experimenter bias)
- Single-blind experiment
- Double-blind experiment
- Subject (participant) effect
- Demand characteristics
- Placebo effect
- Floor effect
- Ceiling effect
Practice effect
if participants took the same math test before and after participating in a special math course, the improvement observed in scores might be due to participants familiarity with and practice on the test items
Fatigue effect
Repeated testing fatigues the participants, and their performance declines as a result
Regression to the mean
Statistical regression occurs when individuals are selected for a study because their scores on some measure were extreme, either extremely high or extremely low. Regression to the mean is a threat to internal validity in which extreme scores upon retesting tend to be less extreme, moving toward the mean.
Instrumentation effect
occurs when the measuring device is faulty. Problems of consistency are more likely when the measuring instrument is a human observer
Mortality (or attrition)
a difference in drop-out rates which results in inequality between the groups.
E.g. Imagine a study to test the effects of a program aimed at reducing smoking. The experimental group participates in the program to reduce smoking, but the heaviest smokers just cannot take its demands and quit. When we take a posttest measure on smoking, only the originally light to moderate smokers are left in the experimental group. Comparing them to the control group is pointless because the groups are no longer equivalent.
Diffusion of treatment
observed changes in the behaviors of participants may be due to information receives from other participants.
E.g. college students are frequently used as participants in research studies. Because many students live near one another and share classes, some may discuss an experiment in which they participated. If other students are planning to participate in the study in the future, the treatment has now been compromised because they know how some of the participants were treated, and this knowledge may affect how they respond, regardless of the condition to which they are assigned.
Solution: short time span planning or ask the participants not to share the information with others
Experimenter effect (or experimenter bias)
the results are biased by the experimenter’s expectations. A researcher may, for example, unknowingly smile more when participants are behaving in the predicted manner and frown or grimace when participants are behaving in an undesirable manner.
Solution:
• Single-blind experiment: either the experimenter or the participants are blind to the manipulation being made
• Double-blind experiment: neither the experimenter nor the participant knows the condition in which the participant is serving; both parties are blind.
Subject (participant) effect
the participant, consciously or unconsciously, affects the results of the study. By:
• Demand characteristics: the subjects try to guess what the experimenter wants as characteristics. Single- or double-blind experiment helps to combat subject effects.
• Placebo effect: the improvement may not be due to the effects of the treatment but to the participant’s expectation that the treatment will have an effect.
