Lecture 2 Flashcards
Beta-
The probability of accepting the null when it is false (type 2 error)
Power
The probability of rejecting the null when it is false or the likelihood of finding differences between conditions when, in fact, the conditions are truly different
Effect size-
A way of expressing the difference between conditions in terms of common metric (across measures and studies). This refers to the magnitude of the difference between two or more conditions. Obtain the difference between the group means and divide by the common (pooled) standard deviation.
History-
Events in addition to the independent variable to which subjects are exposed that could influence their performance on the dependent variable/ Typically these events occur between repeated measurement. This could include events such as news reports, weather or common experience
Maturation-
observed changes as a result of ongoing, naturally occurring processes rather than independent variable. The threat is produced by internal, biological, physical or psychological changes in subjects. This could be physical changes, normal growth, typical developmental progression or typical social and general knowledge gains
Testing-
Subjects performance on a test is affected (or altered) as a result of prior measurement or assessment instead of the independent variable. The before study measures impact the after study measures, rather than the independent variable. Improved performance on the measures may be due to learning, memory and/or practice effects rather than intervention effects.
Instrumentations
Changes in measurement tools or measurement procedures may affect the outcome of the study (does not refer to changes in the study participants. Changes in instruments may occur when outcome variable are not measured in the same way at pre and posttest. Change in the research personnel can occur to the study personnel through experience, become more adept at measurement. In observational studies it may be wise to assess observer drift to see if raters are adhering to the original definitions in the observational protocol
Alpha
The probability of rejecting the null hypothesis when it is true (type 1 error
Beta
The probability of accepting the null when it is false (type 2 error)
Power
The probability of rejecting the null when it is false or the likelihood of finding differences between conditions when, in fact, the conditions are truly different.
Effect size
A way of expressing the difference between conditions in terms of common metric (across measures and studies). This refers to the magnitude of the difference between two or more conditions. Obtain the difference between the group means and divide by the common (pooled) SD.
History
Events in addition to the IV to which subjects are exposed that could influence their performance on the DV. Typically, these events occur between repeated measurement. this could include events such as news reports, weather or common exp.
Maturation
Observed changes as a result of ongoing naturally occurring processes rather than IV. The threat is produced by internal, biological, physical or psychological changes in subjects. This could be physical changes, normal growth, typical dx progression or typical social and general knowledge gains.
Testing
Subjects performance on a test is affected (or altered) as a result of prior measurement or assessment instead of the IV. The before study measures impact the after study measures, rather than the IV. Improved performance on the measures may be due to learning, memory, and/or practice effects.
Instrumentations
Changes in measurement tools or measurement procedures may affect the outcome of the study (does not refer to changes in the study participants. Changes in instruments may occur when outcome variables are not measured in the same way at pre and posttest. Changes in the research personnel can occur to the study personnel through experience - become more adept at measurement. In observational studies it may be wise to ssess observer drift to see if raters are adhering to the original definitions in the observational protocol.
Statistical regression
The changes over time expected in the performance of subjects that occur for statistical reasons, but might incorrectly be attributed to the IV (e.g., treatment). On repeated testing, there is a statistical tendnecy for the scores of any given sample to regress to the mean on any given measure. Thus increases or decreases in score may be a result of statistical regression rather than indicating change resulting from the interventions
Selection biases
participant characteristics may interact with the IV. Age, gender, socioeconomic status, ed. level and ethnicity may play important roles in the response to many interventions and treatments. This threat is very plausible when intact groups (quasi exp). or self-selected participants are used. It is important that during the design phase to determine what characteristics may impact the outcome and exert control accordingly.
Combination of selection and other threats
this may occur when threats to internal validity vary for the different groups within the study. Selection methods may interact with the other threats to internal validity further biasing the results (history, maturation, testing, instrumentation, attrition). Selection-history threat is plausible when one group is exposed to a particular event that a comparison group did not.
Mortality/attrition
differential drop out across conditions at one or more time points that may be responsible for outcomes rather than the intervention itself. The longer and more involved a study is, the higher rate of participant’s attrition. This may make before and after samples non-comparable. Is there an attrition bias such that subjects later in the research process are no longer representative of the larger initial group?
Special Problems involving control groups: Treatment imitation or diffusion
When those in the control group learn of the exp. arrangements or are accidentally exposed to the intervention. Thus, control group members may benefit from info. given to the treatment group. As a result, similar performance on outcome variables occurs between tx and control groups, obscuring any treatment effects.
Special Problems involving control groups: Compensatory rivalry
Occurs when one group, typically the comparison or control group, learns of differences with the other group, typically the experimental or treatment group. Awareness of differences may create feelings of competition, which may bias attributions made to intervention effects. My lead to competitive attitudes where the control group may work harder to compete with the other group.
Special Problems involving control groups: Resentful demoralization
When one group, typically the comparison or control group, learns of differences with the other group, typically the exp or tx group. Awareness of differences may create feelings of deprivation, which may bias attributions made to intervention effects. Control group participants may become discouraged/ angry leading to psych or actual withdrawal from the study. They may also “not try hard” in light of the known differences
Minimize history/maturation by
the use of a control group, selected from the same pop. as the exp. group can help rule out the effects of hx and maturation. Also, the shorter the duration of an exp., the less likely hx and maturation will be a threat.
Minimize testing threat by:
The use of a research design that does not include a pretest caneliminate testing as a potential threat to internal validity. It may also help to use different but equivalent forms of a test for pre and posttest.