Ch 8 Vocab

between-participant design An experiment in which different participants are assigned to each group. Different people are in the control group (the group that serves as the baseline or "standard" condition) and the experimental group (the group that receives some level of the independent variable). posttest-only control group An experimental design in which the dependent variable is measured after the manipulation of the independent variable. pretest/posttest control group design An experimental design in which the dependent variable is measured both before and after manipulation of the independent variable. An advantage to this design is that you ensure that the participants and groups are equivalent at the beginning of the study. Disadvantages to this design are possible increases in demand characteristics and experimenter effects. confound An uncontrolled extraneous variable or flaw in an experiment. It is imperative that psychologists working with humans understand control and potential confounds due to human variability. internal validity The extent to which the results of an experiment can be attributed to the manipulation of the independent variable rather than to some confounding variable. A study with internal validity has no confounds and offers only one explanation for the results. history effect A threat to internal validity in which an outside event that is not a part of the manipulation of the experiment could be responsible for the results. These events are most likely unrelated to the study but may affect the dependent variable. A control group with equivalent participants would help reveal this confound. maturation effect A threat to internal validity in which naturally occurring changes within participants could be responsible for the observed results. Participants mature physically, socially, and cognitively during the course of a study. A control group with equivalent participants would help reveal this confound. The control group would show an increase in the dependent variable even though they haven't received the independent variable. testing effect A threat to internal validity in which repeated testing leads to better or worse scores. This type of testing confound is sometimes referred to as a practice effect. Testing can also result in the opposite of a practice effect, a fatigue effect (sometimes referred to as a negative practice test). regression to the mean A threat to internal validity in which extreme scores, upon retesting, tend to be less extreme, moving toward the mean. Some students will score well on SAT simply by chance or luck. Sports Illustrated cover hex.

instrumentation effect A threat to internal validity in which changes in the dependent variable may be due to changes in the measuring device. These problems usually occur when the measuring instrument is a human observer. mortality (attrition) A threat to internal validity in which differential dropout rates may be observed in the experimental and control groups, leading to inequality between the groups. Not as much of an issue when attrition is equal between groups. diffusion of treatment A threat to internal validity in which the observed changes in the behaviors or responses may be due to information received from other participants in the study.Can be a problem when participants are in close proximity of each other. experimenter effect A threat to internal validity in which the experimenter consciously or unconsciously affects the result of the study. Also referred to as experimenter bias or expectancy effects because the results of the study are biased by the experimenter's expectations. This is avoided by using blind experiments. single-blind experiment An experimental procedure in which either the participants or the experimenters are blind to the manipulation being made. double-blind experiment An experimental procedure in which neither the participant nor experimenter knows the condition to which each participant has been assigned - both parties are blind to the manipulation participant effect A threat to internal validity in which the participant, consciously or unconsciously, affects the results of the study. placebo group A group or condition in which participants believe they are receiving treatment but are not. placebo

An inert substance that participants believe is a treatment.

floor effect A limitation of the measuring instrument that decreases its capability to differentiate between scores at the bottom of the scale. ceiling effect A limitation of the measuring instrument that decreases its capability to differentiate between scores at the top of the scale. external validity generalized.

The extent to which the results of an experiment can be

college sophomore problem An external validity problem that results from using mainly college sophomores as participants in research studies. Most conclusions are based on studies of young people with a late adolescent mentality who are still developing self-identities and attitudes. exact replication Repeating a study using the same means of manipulating and measuring the variables as in the original study. conceptual replication A study based on another study that uses different methods, a different manipulation, or a different measure. Systematic Replication A study that varies from an original study in one systematic way - for example, by using a different number or type of participants, a different setting, or more levels of the independent variable. Correlated-groups design An experimental design in which the participants in the experiment and control group are related in some way. Within-participants design A type of correlated-groups design in which the same participants are used in each condition. Such designs are often referred to as repeated measures designs because we are repeatedly taking measures on the same individuals. Advantages for this design is that you need less participants. It takes less time to conduct. Participants can complete everything in one sessions and instructions only need to be given once. Most importantly, these designs increase statistical power because when its the same person participating in each condition, individual differences are minimized. It provides are purer measure of the true effects of the independent variable. There are disadvantages too. It is open to most confounds plus ordering effects. Carryover effects are of a concern too. These designs are more open to demand characteristics because they get an idea of what is being tested by participating in both conditions. Not workable in testing drugs or memory studies. Order effects A problem for within-participants designs in which the order of the conditions has an effect on the dependent variable. Counterbalancing A mechanism for controlling order effects either by including all orders of treatment presentation or by randomly determining the order for each participant. Latin square A counterbalancing technique to control for order effects without using all possible orders. Matched-participants design A type of correlated-group design in which participants are matched between conditions on variable(s) that the researcher believes is (are) relevant to the study. Matched participants designs share certain characteristics with both between and within participants designs. This design helps get around carry over

effects, thus drug studies can use this design. Advantages: testing effects and demand characteristics are minimized, groups are more equivalent than in a between-participants design and almost as equivalent as within-participant designs, just as powerful statistically as within-participants design because individual differences have been minimized. Disadvantages: Need more participants, if one person drops out the entire pair is lost (mortality even more of an issue), biggest drawback is the matching itself.