Factors that threaten the validity of research findings Material for this presentation has been taken from the seminal article by Don Campbell and Julian Stanley: Experimental and quasi-experimental designs for research on teaching, which was first published as Chapter 5 in N.L Page (1963), Ed., Handbook of Research on Teaching. In my previous article, I have discussed how the validity can be ensured with respect to Quantitative and Qualitative analysis. 4 Statistical Inference The larger the sample size (n) the more confident you can be that your sample mean is a good representation of the population mean. Representativeness of sample, setting and procedures ! Subject Characteristics• Four of many possible characteristics a. Severity of disability b. Socioeconomic level of parents c. Physical strength and coordination d. … Statistical regression 6. A threat to internal validity is the issue of accurate and confident interpretation of its results that is at the center of the discussion of the validity according to (“Threats to internal and external validity – SlideShare.,” n.d.). Research reactivity 7. Threats to Internal Validity in Causal-Comparative Research • Subject Characteristics • The possibility exists that the groups are not equivalent on one or more important variables • One way to control for an extraneous variable is to match subjects from the comparison groups on that variable The following must be controlled to reduce threats to internal validity. External Validity ! Internal validity threats. ; or the building effect of the subject’s mood states on the experiment (boredom, tiredness, etc.) Attrition (experimental mortality) 14 . Testing ; Testing might cue a person in to … • Testing • Problems resulting from repeated measurements • Practice effect • Memory of certain items Threats to Internal and External Validity 1. Eight Threats to Internal Validity (Cont. Timeline: Time is of paramount importance in research. ): 5. Internal Validity (Cont.) EVALUATING THREATS TO INTERNAL VALIDITY• Follows a procedure similar to the experimental research.1. Selection biases 8. In other words, the "n" justifies the means. Threats to Internal Validity II • Maturation • Relates to participants growing older, wiser, stronger, etc. Threats to Internal Validity Threats to Internal Validity Instrumentation: Changes in the measuring instrument Calibration of scales, accelerometers, etc. Must have good internal validity to have good external validity, but doesn’t guarantee good external validity. Behavioral observations: becoming more/less strict or changing criteria Results could be due to changes in the instrument and not the treatment Threats to Internal Validity History ; An event that occurs during the intervention that could have an impact on the results ; Maturation ; Bias from biological, natural, or social events that can bias results; 6 Internal validity threats. Generalizability ! Threats to validity include: Selection--groups selected may actually be disparate prior to any treatment.. Mortality--the differences between O 1 and O 2 may be because of the drop-out rate of subjects from a specific experimental group, which would cause the groups to be unequal.. Others--Interaction of selection and maturation and interaction of selection and the experimental variable. A threat to internal validity is selection, which is selecting participants for various groups in a study. 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