Broadly, validity is about how well-founded the conclusions are that we can make about a research study |
Internal Validity: The extent to which the intervention can be considered to account for the results (as opposed to a confounding variable). Relates to the amount of control researchers had over the study. |
Threats to Internal Validity: |
History Any event during the time of the study other than the independent variable that could account for the results (control for it by no-treatment group & random assignment), |
Instrumentation Changes in the measuring instrument or measuring procedures over time (Develop standard procedures for rating, train observers/raters prior to data collection), |
Diffusion or Imitation of Treatment The intervention given to one group is unintentionally provided to another group (tell participants not to talk to eachother) |
Maturation Changes over time that result from physical/psychological processes within participants (no-treatment group, random assignment), |
Testing The effects that taking a test once can have on subsequent performance (no-treatment group, reduce the number of administrators, use post-test only design), |
Statistical Regression The tendency for extreme scores on any measure to revert to the mean of a distribution when the measure is readministered (No-treatment or wait-list control group) |
Selection Biases Systematic differences between groups before any experimental manipulations or interventions (random assignment), |
Attrition Loss of participants, problem of longitudinal studies (Participants more likely to remain in study if they are doing something interesting, something that has little or no cost or adverse side effects, seems plausible, and is effective) |
Combination of Selection and Other Threats Another threat results in selection bias Differential Selection occurs when the experimental and control groups are selected based on different criteria or when participants are assigned to groups differentially and not by random assignment. |
Special Treatment or Reactions of Controls Control group may receive some special treatment to offset their feelings about not receiving a desirable treatment |
External Validity: The extent to which the results can be generalized to circumstances other than those in the particular experiment. Relates to how true to life (generalizable) the study is. |
Threats to External Validity: |
History/Treatment Interaction Events occurring at time of treatment/intervention may affect outcome (Hard to control this, but can address by extending study beyond impact of uncontrolled event) |
Reactivity of Assessment If awareness of assessment leads people to respond differently (Include some unobtrusive measures) |
Sample Characteristics The extent to which characteristics of the sample represent the target population (control with random selection) |
Interaction Between Sample and Treatment Specific personal characteristics of participants may interact with treatment and influence outcome in a way that is not representative of the population (Include relevant sample characteristics in the design) |
Stimulus Characteristics and Settings Features of the study with which the intervention or condition may be associated (Use multiple experimenters, settings, stimuli) |
Reactivity of Experimental Arrangements The influence of the participants’ awareness that they are participating in an experiment (Archival data, Observational data) |
Multiple-Treatment Interference In some studies, participants are exposed to multiple treatment conditions (counter-balance) |
Novelty Effects The possibility that the effects of an intervention may in part depend on their innovativeness or novelty in the situation |
Test Sensitization The effect of a previous test on subsequent performance (Various group designs (post-test only, Solomon four-group) |
Timing of Measurement The results of an experiment may depend on the point in time that assessment devices are administered |
Construct Validity: The conceptual basis (construct) underlying the effect. Threats impact the conclusions that can be drawn from the findings. |
Threats to Construct Validity |
Experimenter Expectancies Expectations could lead to changes in tone of voice, posture, facial expressions, delivery of instructions, and adherence to the prescribed procedures |
Single Operations and Narrow Stimulus Sampling the intervention includes features that the investigator considers irrelevant to the study, but that may introduce ambiguity in interpreting the findings (a wide range of conditions associated with treatment delivery) |
Attention and Contact with the Clients Differential attention across groups may be the basis for group differences ( To control for this, you would need to include a placebo group and ensure that experimenters are blind to the conditions to which participants are assigned) |
Cues of the Experimental Situation May include information conveyed to prospective participants prior to their arrival to the experiment, instructions, procedures, and any other features of the experiment |
Statistical Conclusion Validity: The extent to which a relation is shown and the extent to which the experiment detects effects if they exist |
The Experimenter Effect: When the experimenter communicates to the participants, most often subtly, what outcomes they would like to achieve |
Other |
interaction between history and treatment effects refers to how events occurring at the time of the intervention or treatment affect the outcome (threat to external ecological validity) |