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PHC 6013: Validity

Validity - precision and bias

QuestionAnswer
What is bias? Any process at any stage of inference which tends to produce results or conclusions that differ systematically from the truth
What is accuracy? The degree to which a variable actually represents what it is intended to represent
Accuracy is a function of what? It is a function of systematic error (bias); the greater the error, the less accurate the variable.
What is the best way to assess accuracy? Comparison with a reference standard
What is the benefit of higher accuracy in a study? Increases validity of conclusions
What is accuracy threatened by? Systematic error (bias) contributed by: observer, subject, instrument
What are the three main classes of measurement error? Observer, instrument, and subject bias
What is a "gold standard"? A reference technique that is considered accurate
What are the major approaches to increasing accuracy? 1) Standardizing the measurement methods 2) Training and certifying the observers 3) Refining the instruments 4) Automating the instruments 5) Making unobtrusive measurements 6) Calibrating the instruments 7) Blinding
Does blinding ensure the overall accuracy of measurements? Explain. No, but it can eliminate differential bias that affects on study group more than another.
What is the difference between validity and accuracy? Validity is a particular type of accuracy that measures how well a measurement represents phenomenons of interest that are subjective and abstract, such as pain or quality of life, for which there is no concrete or gold standard.
What is content validity? How well the assessment represents all aspects of the phenomena under study and often uses subjective judgments about whether the measurements seem reasonable
What is face validity? Subjective judgments; essentially, researchers are simply taking the validity of the test at face value by looking at whether a test appears to measure the target variable
WHat is construct validity? How well a measurement conforms to theoretical constructs
What is criterion-related validity? The degree to which a new measurement correlates with well-accepted existing measures
What is predictive validity? Related to the criterion-related approach to assessing validity, it is the ability of a measurement to predict an outcome
What are the three ways to view and assess validity? Content, construct, and criterion-related
What describes phenomena in terms that can be analyzed statistically? Measurements
What does the validity of a study depend on? How well the variables designed for the study represent the phenomena of interest
What enhances the validity of drawing inferences from the study to the universe? Minimizing measurement error by designing measurements that are relatively precise and accurate
What is the degree to which a variable is reproducible, with nearly the same value each time it is measured? Precision
What has a very important influence on the power of a study? Precision
What is the relationship between precision and power? The more precise a measurement, the greater the statistical power at a given sample size to estimate values and to test hypotheses
What are some other terms for precision?: Reproducibility, reliability, consistency
Precision is a function of what? It is a function of random error (chance variability); the greater the error, the less precise the measurement.
What is systematic error also called? Bias
What is random error also called? Chance variability
What are the three main sources of random error in making measurements? Observer, instrument, and subject variability
How is precision assessed? Through the reproducibility of repeated measurements, either comparing measurements made by the same person/instrument (within-observer/instrument reproducibility) or different people (between-observer/instrument reproducibility).
What is within-observer reproducibility? Measurements made by the same person/instrument
What is between-observer reproducibility? Measurements made by different person/instrument
What are the major approaches to minimizing random error and increasing the precision of measurements? 1) Standardizing the measurements 2) Training and certifying the observers 3) Refining the instruments 4) Automating the instruments 5) Repetition
What strategies should always be used to increase precision of a study? 1) Standardizing the measurements 2) Training and certifying the observers
What is guaranteed to improve precision whenever feasible and affordable? Repeating the measurement
What is precision? The degree to which a variable has nearly the same value when measured several times.
What is the best way to assess precision Comparison among repeated measures
What is the benefit of higher precision in a study? Increased power to detect effects
What is precision threatened by? Random error (chance) contributed by: observer, subject, instrument
What are the sources of systematic error? 1) Selection bias 2) Information bias 3) Confounding
What type of bias is easier to prevent and measure? Information biases (compared to sampling biases)
What are sources of threats to internal validity? 1) Error 2) Bias 3) Confounding
What is the consequence of selection bias? The association between exposure and outcome among those selected for analysis differs from the association among those eligible.
What types/sources of biases fall under selection bias? 1) Bias resulting from inappropriate selec- tion of controls in case-control studies 2) Bias resulting from differential loss-to-follow up 3) Incidence–prevalence bias 4) Volunteer bias 5) Healthy-worker bias 6) Nonresponse bias.
What are the stages of research in which bias can occur? 1) Literature review 2) Specifying and selecting the study sample 3) Applying the intervention (for experimental) 4) Measuring exposures and outcomes 5) Analyzing the data 6) Interpreting the analysis 7) Publishing the results
Created by: AlneciaPHS