Midterm Flashcards
Maturation
Internal Validity Threat
changes that result from processes internal within the participants
Only a problem when the effects of maturation cannot be separated from the effects of the intervention
Often go together with threats due to history
Control group can help mitigate
Single Operations and Narrow Stimulus Sampling
Construct Validity
Sometimes a single set of stimuli, investigator or other facet of the study that the investigator considers irrelevant may contribute to the impact of the experimental manipulation
Also a type of external validity but in construct it’s not about generalizability but rather not being able to separate “active ingredient” from other variables
Threats to External Validity
Multiple-Treatment Interference Sample Characteristics Narrow Stimulus Sampling Reactivity of Experimental Arrangements Reactivity of Assessment Test Sensitization Novetly Effects Generality across Measues, Setting and Time
Mneumonic: M. SNRRTNG
Types of Data-Evaluation Validity
Low Statistical Power
Unreliability of the Measures
Multiple Comparisons and Error Rates
Participant Heterogeneity
Variability in Procedures
Errors in Data Recording, Analysis, and Reporting
Restricted Range of the Measures
Misreading or Misinterpreting the Data Analyses
Menumonic: LUMP VERM
Experimenter Expectancies
Construct Validity
Unintentional effects the experimenter may have that influence the subject’s responses in the experiment
Statistical Regression
Internal Validity Threat
extreme scores tend to change towards the mean over time
no treatment control group helps mediate
protect against:
randomly assign participants to groups
use measures with high reliability and validity
-test participants twice before the intervention and select those who are high on both testings (rarely done)
Purposive Samples
Pick cases that are judged to be typical of the pop of interest
Used to forecast elections
Ex: Picking a number of small election districts whose election returns in previous years have approximated the overall state returns.
Interrelations among Validities
Trade-off between controlling a situation in a study and being able to generalize it
Reactivity of Experimental Arrangements
External Validity Threat
Issue of how partcipants’ knowledge that they are being studied (or in a special program or that a relationship is being examined between specific variables) changes their behavior
History
Internal Validity Threat
Any event inside (except the IV/intervention) or outside of the experiment that may account for the results but it has to be a plausible explanation of the results
Control group can help mitigate
Testing
Internal Validity Threat
Effects of repeated assessment
“practice effect”
group that receives pre and post without intervention can help rule this out
Test Sensitzation
External Validity Threat
Partcipants may respond differently to an intervention because the pretest shows them what the focus of assessment is
Sample Characteristics
External Validity Threat
The extent to which the results can be extended to subjects or clients whose characteristics may differ from those included in the investigation
Variablity in the Procedures
Data-Evaluation Validity
Same as particpant heterogeneity but has to do with procedures, instructions, etc.
Attention and Contact Accorded the Client
Construct Validity
The extent to which increased attention or contact to the client that is associated with the intervention could plausibly explain the effects attributed to the intervention
Placebo group can help mediate this
Special Treatment or Reactions of Control
Internal Validity Threat
control group gets special attention which can be an alternative explanation of the results
Ex: control group is given something so they won’t feel snubbed
Other examples:
- Participants try harder because they know they’re in the treatment group
- Control group tries harder to match Part.
- Control group performs worse because they are let down that they are in control group
Restricted Range of the Measures
Data-Evaluation Validity
A measure may have a very limited range (total score from high to low) and that may interfere with showing group differences.
Not enough variablity in scores to show difference in group
Low Statistical Power
Data-Evaluation Validity
Major threat to DEV
Power is likelihood of demonstrating an effect or group difference when in fact there is a true effect in the world
Can happen when samples are too small (not representative) or too large (too much variability)
Threats to Internal Validity
Statistical Regression Maturation Instrumentation Testing History Selection Biases
Attrition
Diffusion or Imitation Treatment
Special Treatment or Reactions of Controls
Mneumonic: SMITHS ADS
Accidental (Available) Samples
take cases that are available until reach a specifed N (ex: first 100 people on the street)
Demand Characteristics
Construct Validity
Cues of the experimental situation that influence the results
aspects of the instructions, procedures, etc. that are part of the study but not the “active ingredient”
Reactivity of Assessment
External Validity Threat
Participants’ awareness that they are being assessed can alter their responses
Focuses on the measures used and other measurement procedures
When and How Threats to Internal Valdity Occur
- A study is poorly designed and many threats are possible
- A study is designed well but conducted sloppily
- A study is designed well but attrition occurs
- A study is designed well but the results do not allow the conclusion that treatment led to change
Instrumentation
Internal Validity Threat
Changes in how the DV is measured over time
Can occur when any of the following is not constant:
measuring instruments
observers, raters, or interviewers
remarks or directions form the experimenter
test conditions
Most common occurrence is where raters change the criteria they are using over time
Construct Validity
what specific aspects of an intervention are responsible for observed change or an observed effect
Distinguish from contruct validity of a test
considered after threats to internal validity have been ruled out
Cluster Sampling
first sample groupings or clusters, then sample individuals from these
Can be random
used because it is difficult and expensive to get random or stratified random samples
Large-scale surveys often use this method
Aka multistage sampling because of the different stages involved
Diffusion or Imitation of Treatment
some or all of the participants in the control group may inadvertently receive some or all of the treatment (e.g. kids in two classes talk about the treatment during recess)
Also can happen if some people in the intervention group do no receive the intervention
Types of sampling
Probability Sampling
Accidental Samples
Systematic Sampling
Stratified Sampling
Quota Samples
Purposive Samples
Cluster Sampling
Mneumonic: PASS QPC
Types of Validity (4)
Internal
External
Construct
Data-Evaluation
Null hypothesis
specifies there is no differences between groups
Effect size (ES)
magnitude of the difference between two (or more) conditions or groups
M1 - M2/SD
The smaller the variablity (the more we minimize error) the larger the effect size because SD is the denominator
Confounds
factors that varied with the intervention and therefore could explain (be responsible for) the results
Confounds are threats to construct validity
Novelty Effects
External Validity Threat
It is possible that the effect of an experimental manipulation or intervention might in part be due to its novelty
Reactive measures
If awareness of assessment leads persons to respond differently from ow they would usually respond
Obtrusive measures
When subjects are aware their performance is being assessed
Stratified Sampling
members of groups in the pop are selection in proportion to their representation in the pop
Types of contruct validities
Single Operations and Narrow Stimulus Sampling
Experimenter Expectancies
Demand Characteristics
Attention and Contact Accorded the Client
Mneumonic: Single Experimenters Demand Attention
or SADE
Data-Evaluation Validity
Facets of the evaluation that influence the conclusions we reach about the experimental condition and its effects