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A condition, intervention, or characteristic that will predict or cause a given outcome 


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The outcome variable which is either caused by or related to the independent variable 


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Conceptualizing a variable in a form that explicitly states how it is going to be measure quantitatively 


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Labels, names, identifies Mutually exclusive and exhaustive categories No arithmetic manipulation other than counting can be performed Examples: 1=male 0=female, numbers for football players, blood types
Weakest Appropriate stat test: Frequency/chi square 


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Rank order points on a scale (directionally) Numeric values are limited Intervals between items are not known, and are not equal Ex: Educational attainment (0=less than HS, 1=some HS, 2=HS degree, 3=some college, 4=college degree, 5=post college)
Appropriate stat test: frequency/nonparametric tests 


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Definition
Has numeric properties Assume equal amounts between the numbers on the scale equal intervals No true 'zero' amount Example: Temperature on the Farenheit scale, standard numbering of calendar years
Appropriate stat test: parametric/nonparametric tests 


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Definition
Has all the properties of an interval scale In addition, it has a true zero point indicating complete absence of the variable Can form ratios: 10 lbs is twice as heavy as 5 lbs Examples: Weight, temp on Kelvin scale, number of pts visiting a pharmacy
Appropriate stat test: parametric/nonparametric tests 


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Numeric values assigned to a variable consist of limited categories No way to expand your answer Yes or no questions Better, worse, the same 


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A larger range of numeric values are assigned to a variable
Continuous data can be converted to categorical data but not vice versa 


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Precision (tight grouping)/reproducibility Extent to which a repeated measurement of a stable phenomenon by different people and instruments at different times and places produces similar results Range from 0.001.00 Closer to 1.00 = most reliable, closer to 0.00 = most unreliable 


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Accuracy Degree to which the data measure correspond to the true state of the phenomenon being measured (does the instrument measure what it is supposed to measure?) 


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Measure of the strength and direction of a relationship between two variables Range from 1 to 1 Farther from 0 = stronger the correlation 0= random event, no correlation 


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Determine reliability by testing & retesting (blood glucose meter). Use two instruments that assess the same concept Rater reliability: assessed when data is collected for a study by an observer or tester/rater (Used with objective assessments) Intrarater reliability: stability of data recorded by one indicividual Interrater reliability: variability between two or more raters who measure same group of subjects Internal consistency: used with instrument/surveys that use multiple questions/items to measure a single construct 


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Definition
Face validity: instrument appears to test what it is supposed to test (qualitative). Weak Content validity: Method of measurement includes all dimensions of the construct one intends to measure (and nothing more) Construct validity: Degree to which inferences can legitimately be made from the instruments or measures to theoretical constructs that the instrument was supposed to measure 


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Definition
Highly correlated with an already validated scale (gold standard)
2 types: concurrent validity: instrument to be validated and gold standard are administered concurrently predictive validity: relationship btwn the new instrument & the outcomes or gold standard is examined to determine if the new instrument is a good predictor of the outcome/gold standard 


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Definition
Convergent validity: high positive correlation between scores on measurement and another measure reflecting underlying phenomenon Discriminate validity: indicates a low correlation will exist between measure that assess different characteristics 


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Major concept of validity (accuracy) 

Definition
Sensitivity: the proportion of people with disease who have positive test
Specificity: proportion of people without disease who have a negative test 


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Positive predictive value 

Definition
Estimates the likelihood that a person who tests positive actually has the disease PPV= a/a+b 


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Negative predictive value 

Definition
Estimates the likelihood that a person who tests negative is actually disease free 


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Manipulation of the variable? Yes: Experimental design No: Observational Is the comparison group assigned randomly? Yes: True experimental design No: Quasiexperimental design 


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Is the independent variable really associated with the dependent variable? 


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Are the results of our study generalizable? Can our conclusions be applied to the population of interest? 


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Threats to internal validity 

Definition
History, maturation, attrition, testing, instrumentation, statistical regression, selection bias, diffusion of treatment, compensatory equalization of treatments 


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Threats to external validity 

Definition
Interaction of treatment and selection Interaction of treatment and setting Interaction of treatment and history 


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Limiting threats to validity 

Definition
Can be controlled or reduced through appropriate study design, appropriate sample selection, and use of specific inclusion/exclusion criteria Some threats can be further controlled via statistical methods Studies that rely on sound research design to minimize threats to validity are considered more robust 


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Definition
Subjects are randomly assigned to at least two comparison groups Separated by how subjects are assigned to groups 


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Quasiexperimental design 

Definition
Does not meet requirements of true exp design Lacks either randomization or comparison groups (or both) Does have a control measure or multiple measuresn (if not, it is a "nonexperiment") 


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O1 X O2 Observation of group, intervention, then another observation No randomization
Problems: lack of a control group, vulnerable to threats of internal validity 


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Timeseries design ("interrupted") 

Definition
O1O2O3 X O4O5O6 Measures effects of variables over time Based on application of multiple measurements before and after treatment
Advantages: The multiple pretests and posttests act as pseudocontrol conditions because they would help us to recognize if any of the common threats to internal validity were confounding the study Disadvantage: the greatest threat to the internal validity of these studies is history 


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Nonequivalent PretestPosttest control group design 

Definition
O1 X O2  O1 O2
Strongest of all quasiexperimental design as it contains a comparison [control] group (assignment is not random) 


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Definition
Open (nonblinded): Both the investigator and the subjects know about the treatment/placebo assignment Single blinded: only one of them know about the assignment Double blinded: both the investigator and the subject have no knowledge of the assignment 


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Repeated measures design (Crossover design) 

Definition
One group of subjects is exposed to all levels of a treatment variable Washout period between the exposures/interventions 


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Definition
Do not involve manipulation of the independent variable The independent variable is not an active, but an attribute variable An observational study may or may not have a control group Assignment to treatment/exposure cannot be random 


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The study of the distribution of factors that affect health within population groups 


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involves the examination of data that has been collected in the past 


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Involves measurement and data collection starting in the present and going into the future More reliable because the researcher has control of data collection Major disadvantage is time and expense associated with long periods of data collection 


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Conducted at a single point in time and they provide a snapshot of the situation Used in prevalence studies Limitation: temporality problems, can't show that the cause came before the effect 


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Observe subjects over time Researchers make observations over time Aids in the distinction between independent and dependent variable 


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Classifies the occurrence of disease according to person, place and time Aid in generating hypotheses that can be explored by analytic and epidemiologic studies 


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Describe the experience of a patient regarding their disease condition or response to treatment Low internal & external validity Help in generation of inductive hypothesis No control group 


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A proportion reflecting the number of existing cases of a disorder relative to the total population at a given point in time (# of existing cases)/(total population) 


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Quantifies the new cases in the population during a specified time period Represents an estimate of the risk of developing the disease during that time (# of new cases)/(total population at risk) 


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indicates the likelihood that someone who has been exposed to a risk factor will develop the disease, as compared with one who has not been exposed (incidence among exposed)/(incidence among nonexposed) 


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Definition
How much disease that occurs that can be attributed to a certain exposure The amount or proportion of disease incidence that can be attributed to a specific exposure (incidence among exposed)(incidence among nonexposed) 


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Number needed to treat (NNT) 

Definition
The number of people we must treat in order to prevent one adverse event or produce one benefit 


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Number needed to harm (NNH) 

Definition
the number of people that must be exposed to a risk to cause one adverse event Use to examine the effect of a harmful exposure 

