Analysis of Variance Lead Author(s): Main.NancyHills The term analysis of variance (ANOVA) describes a group of inferential statistical tests that were developed...
Ascertainment Bias In scientific research, ascertainment bias occurs when false results are produced by non random sampling and conclusions made about an entire ...
Assumptions: Cumulative Incidence and Incidence Rate Lead Author(s): Jeff Martin, MD Assumption No Temporal/Secural Trends Calculating cumulative incidence with...
Baseline Data Lead Author(s): Information gathered at the beginning of a study from which variations found in the study are measured. A person's health status bef...
Bernoulli distribution In probability theory and statistics, the Bernoulli distribution, named after Swiss scientist Jakob Bernoulli, is a discrete probability di...
Confounding Bias Lead Author(s): Jeff Martin, MD Properties of a True Confounder Is the exposure (or predictor variable), marked E, associated with disease (or...
Reducing Confounding During Data Analysis Lead Author(s): Jeff Martin, MD Methods for Reducing Confounding During Data Analysis: Stratification In the data a...
Properties of a Confounder Association with Disease Lead Author(s): Jeff Martin, MD Refined Properties of a True Confounder Association with Disease When w...
Properties of a Confounder Association with Exposure Lead Author(s): Jeff Martin, MD Refined Properties of a True Confounder Association with Exposure Wh...
Confounder or Intermediate Variable? Lead Author(s): Jeff Martin, MD What Is Not A Confounder? A variable that is an intermediate step in the causal path under s...
Types of Confounding Bias Lead Author(s): Jeff Martin, MD Magnitude and Direction of Confounding After adjusting for confounding variables, we will have a measur...
Bias or Systematic Error (Validity) Lead Author(s): Jeff Martin, MD Origin of the Term Bias Bias refers to a systematic error. The origin of the word appears to...
Measurement Bias Lead Author(s): Jeff Martin, MD Technical Definition: It is the bias, or deviation from the truth, that it is caused when any measurement collec...
Selection Bias Technical definition: Bias that is caused when individuals have different probabilities of being included in the study according to relevant study...
Selection Bias Analytic Study Lead Author(s): Jeff Martin, MD Unbiased Sampling in Analytic Studies In an analytic study or case control study, we are looking ...
Selection Bias Cohort Study or Randomized Clinical Trial Selection Bias in Cohort Studies Less Likely Among initially selected subjects, selection bias in a co...
Selection Bias Cross Sectional Study Lead Author(s): Jeff Martin, MD Cross sectional Study Design As seen in the diagram below, there is an underlying cohor...
Selection Bias Descriptive Study Lead Author(s): Jeff Martin, MD Unbiased Sampling in Descriptive Studies Here is a schematic representation of what we hope ...
Case Control Odds Ratio Lead Author(s): Jeff Martin, MD Case Control Odds Ratio Odds ratio (OR) of exposure in cases and controls is the measure of association ...
Case Control Study Lead Author(s): Jeff Martin, MD Case Control Design The main advantage of case control designs is that it allows you to sample the experienc...
Box Plot Lead Author(s): Erin Dienes Definition of Box Plot A box plot, also known as a box and whiskers plot, is a graphical method that is based on the quar...
Causal Diagrams or Directed Acyclic Graphs (DAGs) Lead Author(s): Jeff Martin, MD Definition of Causal Diagrams The stick and box figure below is known as a c...
Censoring Lead Author(s): Jeff Martin, MD Three Ways Censoring Occurs 1) Death (if death is not the study outcome) 2) Loss to follow up (refuse, move, or canno...
Chi Square versus Fisher's Exact FORUM QUESTION: Julia St George 22 May 2009 12:00 Can you explain the difference between Fisher's exact test and the chi sq...
Clinical Bias The study of medical conditions begins with anecdotal reports. By their nature, such reports only include those referred for diagnosis and treatment...
Clinical Epidemiology Epidemiology is the study of factors affecting the health and illness of populations, and serves as the foundation and logic of intervention...
Cohort Study Lead Author(s): Mark Pletcher, MD; Jeff Martin, MD Definition of a Cohort Study In a cohort study, the study base is an explicitly defined group of...
Common Rule Lead Author(s): Jeff Martin, MD Minimal risk means that the probability and magnitude of harm or discomfort anticipated in the research are not greate...
Confidence intervals (CIs) Lead Author(s): Main.PeterBacchetti These are used to indicate the uncertainty around an estimated or observed association, difference,...
Return to CTSpedia Web Home Conflicts of interest Physicians should not allow a conflict of interest to influence medical judgment. In some cases, conflicts are...
Continuous Random Variable A continuous random variable is one that can assume values corresponding to any of the points contained in an interval. Some examples i...
Cost Effectiveness Analysis A cost effectiveness analysis compares decisions based on units of money per health outcome. For example, dollars per life saved, dol...
Cox and Proportional Hazard FORUM QUESTION: Main.BarbaraGrimes 24 Aug 2009 13:09 If the proportional hazards assumption is not met for a predictor in a Cox m...
Cross Sectional Study Lead Author(s): Jeff Martin, MD Definition of a Cross Sectional Study A cross sectional study can be described as a sample of a populatio...
Decision Analysis Lead Author(s): Clay Johnston, MD, PhD Decision analysis is an explicit, quantitative method for making (or at least thinking about) decisions i...
Mean The mean, also called the average or the arithmetic mean , is often used as a summary of the center of a set of numbers, such as the ages of all the parti...
Median The median of a set of quantitative data (a set of numbers) is the middle number when the measurements are arranged in ascending or descending order. Supp...
Mode The mode is the measurement that occurs most frequently in the data set. The mode is a measure of central tendency as it shows where the data tend to concent...
Reliability Lead Author(s): Erin Esp Definition Reliability is the consistency of a set of measurements or of a measuring instrument. In short, reliability ...
Robust Statistics A robust statistic is a statistic that is resistant to errors in the results caused by outliers or other small departures from model assumption...
Degrees of Freedom Lead Author(s): Main.ErikGregory Definition of Degrees of Freedom To perform t tests we often need to determine the number of degrees of free...
Outcome or Dependent Variable In regression models, these terms refer to the variable that is to be predicted or explained in terms of the predictor or independen...
Difference versus Ratio Lead Author(s): Jeff Martin, MD Ratio versus Difference in Cohort Study There are two basic ways to compare measures of association in ...
Example: Age Adjust Petrochemical Workers Lead Author(s): Jeff Martin, MD Person Time Rates for Cohort Analysis In Austin's (1983) study of petrochemical worke...
Example: Backwards Strategy MRSA Lead Author(s): Jeff Martin, MD Kleinbaum provides an example of using backwards strategy to adjust for potential confounders. ...
Example: Selection Bias Nuclear Bomb Testing Lead Author(s): Jeff Martin, MD Example of Selection Bias: Leukemia and Nuclear Bomb Testing History Smoky Atom...
Example: Selection Bias Breast Cancer Lead Author(s): Jeff Martin, MD Breast Cancer Study This is an example of selection bias in a cross sectional study. Kel...
Example: Selection Bias Pancreatic Cancer Lead Author(s): Jeff Martin, MD Bias in Analytic Study: Coffee and Pancreatic Cancer Study 1: Biased Overestimate ...
Example: Bias Study of Spermicide Use and Down Syndrome Lead Author(s): Jeff Martin, MD Analysis of Spermicide Use and Down Syndrome Data We are looking at ...
Example: Selection Bias in Politics Lead Author(s): Jeff Martin, MD Examples of Selection Bias in Political Studies 1948 Presidential Election The 1948 preele...
Case Control Study Example Netherlands Cohort on Vitamin Intake Lead Author(s): Jeff Martin, MD Abstract from Zeegers (Zeegers' abstract) below is an example ...
Example of Case Control Study Design Kaiser Sigmoidoscopy Study Lead Editor(s): Jeff Martin, MD Case Control Study Design Choices Kaiser Research Division 199...
Case Control Study Example Rare Disease Lead Author(s): Jeff Martin, MD Rare Disease Assumption The rare disease assumption says that if the incidence of ...
Example: Cohort Study Framingham Lead Author(s): Jeff Martin, MD Framingham Study Impact of Diabetes The Framingham Study reports on the impact of diabetes...
Example: Counfounding Bias HIV and Needlestick Lead Editor(s): Jeff Martin, MD Treatment after HIV Needlestick Exposure An example of counding can be found i...
Example: Confounding Bias Night Lite Lead Author(s): Jeff Martin, MD Example of Confounding: Night Lite Confounding can be found in Quinn's study of myopia and...
Example: Cumulative Incidence Denominator GI Illness Lead Author(s): Jeff Martin, MD GI Outbreak MMWR reported "Pleisomonas shigelloides and Salmonella sero...
Example: Cumulative Incidence SEER Program Lead Author(s): Jeff Martin, MD Long Term Survival NCI SEER Program In the following example from Brenner, th...
Example of Differential Misclassification Bias Nurses Health Study Melanoma Risk Lead Author(s): Jeff Martin, MD Differential Misclassification of Exposure...
Example of Differential Misclassification Bias Pregnancy and Congenital Malformations Lead Author(s): Jeff Martin, MD Differential Misclassification of Exposur...
Example: Cumulative Incidence Survival Lead Author(s): Jeff Martin, MD Cumulative Incidence McDonald reports cumulative incidence at four 5 year time interval...
Example: Incidence Reporting What Is Missing? Lead Author(s): Jeff Martin, MD Measures Loosely Called Incidence Number of Events (E) Count of the number of ...
Examples of Incident Density Sampling Dynamic Primary Study Base Lead Author(s): Jeff Martin, MD Example 1: Alcohol Consumption and Breast Cancer The abstract...
Example: Qualitative Interaction Pregnancy and Coffee Study Lead Author(s): Jeff Martin, MD Study of Effects of Caffeine Consumption on Delayed Conception S...
Example: Intermediate Variable CAD Lead Author(s): Jeff Martin, MD Is HDL a Confounder or an Intermediary? We are looking at the relationship between exer...
Example: Intermediate Variable HIV CCR5 Lead Author(s): Jeff Martin, MD CCR5 Receptor on the CD4 Cells Taylor published findings on the human cellular recept...
Example: Selection Bias Loss to Follow Up AIDS Lead Author(s): Jeff Martin, MD Losses to follow up are a grave problem in AIDS studies. Progression to AIDS ...
Example: Lost to Follow up HCV and HIV Lead Author(s): Jeff Martin, MD Many times lost to follow up data is not presented. First Example from a Study with HI...
Graphical Examples of Misclassification Bias Lead Author(s): Jeff Martin, MD The effects of reduced sensitivity of the exposure measurement and/or reduced specifi...
Example of Misclassification Bias Non Differential Exposure Cohort Study Lead Author(s): Jeff Martin, MD Figure Misclassification of Exposure Variable Fle...
Example of Misclassification Bias Non Differential Exposure Imperfect Sensitivity Lead Author(s): Jeff Martin, MD Measurement bias is affected by imperfect s...
Example of Misclassification Bias Non Differential Exposure Imperfect Specificity Lead Author(s): Jeff Martin, MD Measurement bias results from imperfect spec...
Example of Misclassification Bias Non Differential Misclassification of Outcome Lead Author(s): Jeff Martin, MD Misclassification of the outcome results in meas...
Example of Misclassification Bias Outcome Variable Cohort Study Lead Author(s): Jeff Martin, MD Misclassification bias of the outcome variable does not reduc...
Example of Misclassification Bias Pertussis Vaccine 100% Specificity Lead Author(s): Jeff Martin, MD Misclassfication Bias In a cohort study we have a s...
Example of Misclassification Bias Imperfect Sensitivity and Specificity Lead Author(s): Jeff Martin, MD Measurement bias is affected by imperfect sensitivity a...
Example: Do Not Adjust Lung Cancer and Matches Lead Author(s): Jeff Martin, MD Crude and Adjusted Data Here is an example of what can happen when you adjust ...
Example: Person Time Incidence Pediatric Cardiomyopathy Lead Author(s): Jeff Martin, MD Study of Pediatric Cardiomyopathy Lipshultz 2003 Study presents: ...
Examples of Reporting or Ignoring Interactions Lead Author(s): Jeff Martin, MD These are guidelines for reporting or ignoring interactions. First consideration mu...
Example: Stratification Matches, Smoking, and Lung Cancer Lead Author(s): Jeff Martin, MD Reason for Stratification In the example below we are concerned abou...
Example: Incidence Time Varying Exposure Lead Author(s): Jeff Martin, MD Analysis of Changing Exposure and Disease Incidence Ray (2002) analyzed Medicaid rec...
Epidemiology Lead Author(s): Jeff Martin, MD Definition of Epidemiology The study of the distribution and determinants (causes) of disease e.g., cardiovascul...
Error in Clinical Research Lead Author(s): Jeff Martin, MD Missing the Truth What are the ways of missing the truth (ie getting the wrong answer)? There are two ...
Fisher's Exact Test Fisher's exact test is a statistical significance test used in the analysis of tables where sample sizes are small. It is named after its in...
Follow up Time Lead Author(s): Laurel Beckett, PhD; Jeff Martin, MD Definition of Follow up Time Example of Follow up Time Among 250 total subjects, 100 died d...
Framingham Heart Study The Framingham Heart Study is a cardiovascular study based in Framingham, Massachusetts. The study began in 1948 with 5,209 adult subjects ...
Geocoding There are multiple options and many resources on the Internet for learning how to geocode; in this case, for assigning an exact location to study partic...
Geometric Mean The geometric mean is often used to describe the center of a set of numbers that are right skewed, such as the C reactive protein values of partici...
Gold Standard Lead Editor(s): Jeff Martin, MD Gold Standard Individual measurements are the gold standard. Gold Standard in Confounding When considering all...
Group Randomized Study A group randomized study is a randomized trial in which the intervention is assigned to a group of people but the outcome is asses...
Halo effect The halo effect refers to a cognitive bias whereby the perception of a particular trait is influenced by the perception of the former traits in a sequ...
Hosmer Lemeshow Test (H L Test) Lead Author(s): Peter Bacchetti, PhD This provides a p value for the composite null hypothesis that a logistic regression model ha...
Use of Incidence Rate Compare Disease Incidence in a Cohort with Population Lead Author(s): Jeff Martin, MD Advantage of Using Incidence Rate There are a nu...
Compare Incidence from Time Varying Exposure Advantage of Using Incident Rates There are a number of advantages to using incident rates. One of them is to look ...
Use of Incidence Rate Calculate from Population Based Registries Advantage of Using Incidence Rate There are a number of advantages of rates. One is the abil...
Inference Lead Author(s): Jeff Martin, MD The goal of any study is make an accurate (true) inference or to find the truth about the source. There are two types o...
Integrated Data Repository An integrated data repository (IDR) containing aggregations of clinical, biomedical, economic, administrative, and public health data...
Interactions versus Confounding Lead Author(s): Jeff Martin, MD Confounding vs Interaction How do confounding and interaction differ? Confounding: An extraneous ...
Multiplicative Interaction Lead Author(s): Jeff Martin, MD Definition of Multiplicative Interaction When there is interaction in terms of the ratio measure of ...
Additive Interaction Lead Author(s): Jeff Martin, MD Definition of Additive Interaction When there is interaction in terms of the difference measure of assoc...
Graphical Approach to Interaction Lead Author(s): Jeff Martin, MD Many texts use a graphical approach to depict interaction. To determine interactions we graphica...
Intra Class Correlation (ICC) In planning group randomized studies, we typically assume that the measurements between any pair of people in the same group have th...
Jackknife Jackknifing, which is similar to bootstrapping, is used in statistical inferencing to estimate the bias and standard error in a statistic, when a random...
Kaplan Meier Method for Calculating Cumulative Incidence Calculating Cumulative Incidence with the Kaplan Meier Method To calculate cumulative incidence we must ...
Explaining Low Kappa Value FORUM QUESTION: Main.BarbaraGrimes 05 Feb 2010 15:44 I have a set of data where 3 reviewers classified 20 subjects. The client is ...
Length Bias Lead Author(s): Erik Gregory Definition of Length Bias Length bias refers to our tendency to select relatively long intervals of time when doing cr...
Likelihood The likelihood is defined as the probability of observing a given set of data, assuming a particular model of the process that generated them. It is o...
Likelihood Ratio Test This calculates a P value for a term in a regression model based on how much the likelihood worsens when the term is removed from the model...
Linear Regression Lead Author(s): Erin Dienes Definition of Linear Regression Regression analysis is a statistical methodology that utilizes the relationship b...
Linear Splines Lead Author(s): Peter Bacchetti, PhD A linear spline is used in regression models to allow a predictor to have a non linear effect on the outcome. ...
2 log likelihood ( 2 log L) Lead Author(s): Peter Bacchetti, PhD This is a measure of how well the fitted model matches the observed values of the outcome or depe...
Main.PeterBacchetti 22 Oct 2009 Outcome for Logistic Regression Lead Author(s): Peter Bacchetti, PhD For logistic regression, the outcome variable is generally a...
Logistic Regression Lead Author(s): Jeff Martin, MD Definition of Logistic Regression Logistic regression is the method of multivariable analysis used most often...
Lost to Follow up Lead Author(s): Jeff Martin, MD Main Threat to Validity in a Cohort Study "What is the effect of subjects who are lost to follow up on the in...
Maximum Likelihood Estimation This is a general strategy for estimating the parameters of a statistical model of the process that generated a set of data. The par...
Measure of Central Tendency The central tendency of a set of measurements is the tendency of the data to cluster/center around certain numerical values. Some exa...
Medpedia http://www.medpedia.com The Medpedia Project is a long term, worldwide project to evolve a new model for sharing and advancing knowledge about health, me...
Median Reporting FORUM QUESTION: Main.BarbaraGrimes 06 Jul 2009 09:53 When the median of a measurement is reported in a manuscript, should the min,max or the...
Meta Analysis Lead Author(s): Clay Johnston, MD, PhD The clinical literature is overwhelming. On any topic important to clinical decision making, there are numer...
Minimal Risk According to the Common Rule, Minimal risk means that the probability and magnitude of harm or discomfort anticipated in the research are not...
Missing Data FORUM QUESTION: Julia St George 22 May 2009 11:44 I have done a survey of interns in which each person was asked 12 questions, before and after ...
Overview In 2006, the Clinical and Translational Science Institute (CTSI) was established at UCSF to aid researches in their work. From this, the Academic Researc...
Negative Confounding Lead Author(s): Jeff Martin, MD Definition of Negative Confounding When the measure of association has gotten larger after accounting for ...
Return to CTSpedia Web Home Nested Case Control Study This article is from Wikipedia; the original article is Nested case control study . The list of authors can...
Normal Distribution Lead Author(s): Erin Dienes The Normal distribution (also known as the Gaussian distribution or a bell curve ) is a type of pattern that a ...
Null Hypothesis Lead Author(s): Jeff Martin, MD The null hypothesis says that neither the exposure, the effects of treatment, or the resulting disease differed be...
Main.PeterBacchetti 21 Jun 2012 Numeric Variable This is a variable that is measured as a number on a quantitative scale, such as weight in kilograms or age in y...
Odds RatioThis is a measure of the association between a predictor (or independent) variable and a yes or no (binary) outcome (or dependent) variable. * A val...
Odds Ratio Expressions FORUM QUESTION: Julia St George 27 May 2009 11:09 I ran a logistic regression model and got an estimated odds ratio showing that whe...
Odds Ratio Lead Author(s): Jeff Martin, MD Odds Ratio = Four Probabilities Odds are already the ratio of two probabilities, so the odds ratio involves four pro...
Odds Ratio versus Risk Ratio Lead Author(s): Jeff Martin, MD Comparing OR and Risk Ratio OR Farther from 1 The schematic below illustrates the point that, unle...
Odds and Probability Lead Author(s): Jeff Martin, MD Odds = Probability of an Event Odds are most simply calculated as the number of events divided by the number...
Outcome or Dependent Variable Lead Author(s): Jeff Martin, MD Definition of Outcome or Dependent Variable These terms refer to the variable that is to be predict...
Partial Least Squares (PLS) Lead Author(s): Danh Nguyen, PhD Partial least squares can be viewed as a dimension reduction method that reduces the dimension of the...
Polynomial Model Lead Author(s): Peter Bacchetti, PhD A polynomial model is used in regression models to allow a predictor to have a non linear effect on the outc...
Study Precision Good Precision Good Validity Consider that at the center of the target is the truth and that each shot at the target represents a study you con...
Predictor or Exposure Variable Lead Author(s): Jeff Martin, MD This variable is also referred to as the exposure, the explanatory variable, or the independent va...
Prevalence Ratio in Cross Sectional Study Lead Author(s): Jeff Martin, MD Definition of Prevalence Ratio The ratio of the proportion of the persons with disea...
Profile Likelihood Confidence Intervals The profile likelihood method determines lower and upper confidence bounds for a model parameter, such as a fitted regress...
Quadratic P value Lead Author(s): Peter Bacchetti, PhD This is a P value for the hypothesis that a numeric predictor has a linear effect. When P 0.05, this is us...
Random Error Chance (Reproducibility) Lead Author(s): Jeff Martin, MD Definition of Random Error In distinction to systematic error or bias, random error occu...
Randomized Trial A Type of Cohort Study Lead Editor(s): Jeff Martin, MD Randomized Trial * Randomized trial is a cohort design with exposure assigned rath...
Rate and Cumulative Incidence Lead Author(s): Jeff Martin, MD Rate Reserved for Measuring Incidence Rate should be reserved for measuring incidence. * In ge...
Measure of Association Rate Ratio Definition of Rate In a cohort study: Rate is based on events per person time = incidence rate We have limited the use of t...
Receiver Operating Characteristic Curve A receiver operating characteristic (ROC) curve is used to make an assessment of the overall value of a new diagnostic te...
Relational Databases This presentation by Dr. Michael Kohn of UCSF gives a great introduction to the topic, and offers the following guidelines for data managemen...
Relative RiskAlso called the Risk Ratio.This is a measure of the association between a predictor (or independent) variable and a yes or no (binary) outcome (or de...
Rescaled Predictors In regression models with a numeric predictor, the estimated effect is that associated with a 1 unit increase in the predictor. In some cases,...
Residuals Not Normally Distributed FORUM QUESTION: Main.ErinMadden1 03 Sep 2010 16:20 For a linear regression where the residuals are not normally distribute...
Risk Factor A risk factor is a variable associated with an increased risk of disease or infection. Risk factors are correlational and not necessarily causal, beca...
Prevalence of Risk Factor Lead Author(s): Jeff Martin, MD Definition of Prevalence of Risk Factor The prevalence of a risk factor is also important from a publ...
Risk Ratio versus Rate Ratio Lead Author(s): Jeff Martin, MD RR Relative risk or RR is very common in the literature, but may represent: * a risk ratio, * ...
Measure of Assocation Risk Ratio Lead Author(s): Jeff Martin, MD Definition of Risk In a cohort study: Risk is based on proportion of persons with disease = ...
Stata Stata is a general purpose statistical software package created in 1985 by StataCorp. It is used by many businesses and academic institutions around the wor...
Case Control Design Sampling at Baseline Special type of case control study: Case cohort design Lead Editor(s): Jeff Martin, MD Summary of Case Control Sampli...
Case Control Design Sampling Controls at Follow up Lead Author(s): Jeff Martin, MD Summary of Case Control Sampling Design Sampling Measure of Associat...
Case Control Design Incidence Density Sampling CUT Lead Author(s): Jeff Martin, MD Summary of Case Control Sampling DesignSamplingMeasure of Association Ca...
Case Control Design Incident Density Sampling Dynamic Primary Study Base Lead Author(s): Jeff Martin, MD Case Control Incidence Density Sampling in a Dynami...
Sampling ANCHORS Lead Author(s): Jeff Martin, MD Definition of Sampling * Sampling is the process by which individuals belonging to a larger target population...
Skewed Variable A skewed variable has a distribution where there are a few observations that are much larger (right skewed) or smaller (left skewed) than the othe...
Standardized Mortality Ratio Standardized Mortality Ratio In the example of petrochemical workers: * If U.S. death rates for age sex race calendar period grou...
Stand Alone Data Entry Main.KnutWittkowski 26 Jun 2009 08:31 Michael, EpiInfo is using MS Access for both the data and the meta data. Do you have any suggest...
P values Lead Author(s): Peter Bacchetti, PhD These are usually interpreted as showing the strength of evidence against the possibility that there is truly no ass...
Stata Commands Here are several sites that have Stata commands you may find useful (by no means an exhaustive list): University of Chicago, Department of Statisti...
Statistical Test Needed FORUM QUESTION: Julia St George 22 May 2009 12:12 I found that 0 of 63 patients responded to an alternative therapy, but when I subm...
Stratification Lead Author(s): Jeff Martin, MD Definition of Stratification Forming separate strata or groups during study analysis or during study design. #S...
Study Analysis: 2 x 2 Table or Chi square Test Lead Author(s): Jeff Martin, MD Measuring Association The simplest way to measure the association is to have a dic...
Adjustment The method of modifying observations to account for external factors that may distort or skew associations in observations. Adjusted Measure of Assoc...
Backwards Strategy Lead Author(s): Jeff Martin, MD Backwards Strategy for Potential Confounders In the Backwards Strategy we initially evaluate all potential co...
Bias Variance Tradeoff Lead Author(s): Jeff Martin, MD Bias Variance Tradeoff * What is a meaningful difference between the crude and adjusted measure of ass...
Forwards Strategy Lead Author(s): Jeff Martin, MD Forwards Strategy for Potential Confounders In contrast to the backwards strategy for potential condunders t...
Inappropriate Statistical Testing for Confounding Lead Author(s): Jeff Martin, MD Examining a Known Confounder Testing for statistically significant differenc...
Life Tables Lead Author(s): Jeff Martin, MD Definition of Life Tables Life tables, as the name implies, were first constructed to look at the cumulative surviv...
Summary Estimators: Mantel Haenszel Method Lead Author(s): Jeff Martin, MD This is one method for calculating summary adjusted estimators when making adjustments...
Adjustment for Multiple Confounders Lead Author(s): Jeff Martin, MD Stratification of Multiple Confounders with More Than Two Levels Stratification can also be...
Obtaining the Denominator for Person Time Rates Lead Author(s): Jeff Martin, MD There are two methods for obtaining the denominator for person time rates. Meth...
Study Analysis Plan Lead Author(s): Jeff Martin, MD When Written Written before the data are analyzed Study Analysis Plan Content * Detailed description ...
Association Lead Author(s): Jeff Martin, MD Definition of Association * Relationship between two or more events or variables. Measuring Disease Association ...
Measure of Association Risk Difference Lead Author(s): Jeff Martin, MD Why Use Risk Difference? Risk difference gives an absolute measure of the association ...
Study Base Lead Author(s): Jeff Martin, MD Definition of a Study Base A study base, also called a reference population, is a defined population whose disease exp...
Primary Study Base A study base, also called a reference population, is a defined population whose disease experience during some period of time is the source of...
Secondary Study Base Lead Editor(s): Jeff Martin, MD A study base, also called a reference population, is a defined population whose disease experience during so...
Cohort Lead Author(s): Jeff Martin, MD Definition of a Cohort Any well defined population can be thought of as a cohort that continues to recruit new subjects...
Study Design Strength of design rests on accurate measurements made prior to the outcome, not whether it is cohort or case control sampling Jeff Martin, MD Main...
Study Design Elements Study Design Element 1: Identify the Population The first key element in study design that uses observation of individuals is to identify t...
Disease Occurrence Lead Author(s): Jeff Martin, MD Measuring Disease Occurrence Occurrence of disease is the fundamental outcome measurement of epidemiology Oc...
Incidence Lead Author(s): Jeff Martin, MD Definition of Incidence Incidence counts new disease diagnoses during a defined time period. Incidence vs Prevalence...
Cumulative Incidence Person Time Lead Author(s): Jeff Martin, MD Definition of Cumulative Incidence The proportion of individuals who experience the event...
Incidence Rate Using Person Time Lead Author(s): Jeff Martin, MD Definition of Incidence Rate Using Person Time The number of events divided by the amount of p...
Prevalence Lead Author(s): Jeff Martin, MD #PrevalentTerm Definition of Prevalence Prevalence counts existing disease diagnoses, usually at a single point in ti...
Period Prevalence Lead Author(s): Jeff Martin, MD Definition of Period Prevalence Period prevalence is the number of persons with a specific disease at one ...
Point Prevalence Lead Author(s): Jeff Martin, MD Definition of Point Prevalence Point prevalence is the number of persons with disease in a time interval (eg...
When Is Study Done? Lead Author(s): Jeff Martin, MD Prospective and Retrospective Prospective and retrospective refer to when the study is done in relation to th...
Interaction Effect Modifier Lead Author(s): Jeff Martin, MD Definition of Interaction When the magnitude of a measure of association * between exposure and di...
Matching Lead Author(s): Jeff Martin, MD Definition of Matching Definition of Matching: * Match unexposed or non case subjects to those of the comparison ...
Randomization Definition of Randomization Definition of Randomization: random assignment of subjects to exposure (e.g., treatment) categories One of the three...
Restriction Lead Author(s): Jeff Martin, MD Definition of Restriction Definition of Restriction: Restrict enrollment to only those subjects who have a specific...
Unit of Observation Lead Author(s): Jeff Martin, MD Study design begins with the unit of observation( note diagram). Either the observations are: * Made on i...
Type 3 p value This is a p value for the composite null hypothesis that all levels of a categorical predictor have the same effect on the outcome as the reference...
Validity Lead Author(s): Jeff Martin, MD Types of Validity There are two types of validity: * Internal : Inference from the study sample to the source populat...
External Validity or Generalizability Lead Author(s): Jeff Martin, MD What is External Validity or Generalizability? External validity is a measure of how well ...
Measurement Validity Sensitivity Lead Author(s): Jeff Martin, MD What Is Sensitivity? Sensitivity is the ability of a measurement to identify correctly those...
Measurement Validity Specificity Lead Author(s): Jeff Martin, MD What Is Specificity? Specificity is the ability of a measurement to identify correctly those...
Internal Validity Lead Author(s): Jeff Martin, MD What Is Study or Internal Validity? Study validity is what we refer to as internal validity or a measure of how...
Value Column Lead Author(s): Jeff Martin, MD In output from regression modeling macros, this gives the particular level of a categorical predictor that the result...
Intermediary Variable Lead Author(s): Intermediary Variable Is Not a Confounder As seen in the diagram below a variable that is an intermediate step in the causa...
Third Variable: Intermediate, Effect Modifier, Confounder or No Effect Lead Author(s): Jeff Martin, MD Third Variable When evaluating association between an expo...
Variable Column Lead Author(s): Peter Bacchetti, PhD In output from regression modeling macros, this column gives the name of the predictor or independent variab...
Web based Interactive System for Study Design, Optimization and Management (WISDOM) WISDOM for Web based Interactive system for Study Design, Optimization, and M...
Analysis of Variance Lead Author(s): Main.NancyHills The term analysis of variance (ANOVA) describes a group of inferential statistical tests that were developed...
Common Biostatistical Problems 1 P values for establishing negative conclusions 1 Misleading and vague phrasing 1 Speculation about low power 1 Exclu...
Correlation Lead Author(s): Main.NancyHills Measures of correlation are not statistical tests of inference, but are actually descriptive statistical measures whic...
Estimation versus Hypothesis Testing Lead Author(s): George Howard, DrPH Inference ESTIMATION Statistics in Estimation Repeated Estimates Uncertainty in ...
Geocoding: What is it and why is it necessary? This article is derived from materials created by Dr. David Rehkopf. Geocoding involves assigning an exact location...
Avoiding Insufficient or Excessive Precision How many decimals to give is a common practical issue in reporting the results of statistical analyses in publication...
Infinite Estimates Lead Author: Peter Bacchetti, PhD Some regression methods, notably logistic regression and Cox proportional hazards regression, can produce de...
Interval Censored Survival Analysis Primary Author: Main.JohnKornak Description Survival analysis methods play an important role in the statistical analysis of...
Career Development Awards, K Series Lead Author: Tom Mitchell Types of Mentored Career Development Awards * There are a number of different mentored K awards ...
Logarithmic Transformation Lead Author(s): Peter Bacchetti, PhD Statistical models are sometimes more meaningful and accurate if outcome or predictor variables ...
Longitudinal Cohort Studies Lead Author(s): Jeff Martin, MD A longitudinal study is a correlational research study that involves repeated observations of the same...
Common Biostatistical Problems and the Best Practices that Prevent Them This is based on Peter Bacchetti's lecture on "Common Biostatistical Problems and the Bes...
Main.PeterBacchetti 16 Jun 2012 In a study of how long participants survive or how long they go without experiencing a particular event of interest, fully describ...
Reporting Power Lead Author(s): Peter Bacchetti, PhD Power calculations are widely recognized to be irrelevant in the interpretation of completed studies, becaus...
Proper Interpretation of Results Lead Author: Peter Bacchetti, PhD This page provides general conceptual guidance on interpreting results of statistical analyses ...
Current Sample Size Conventions: Flaws, Harms, and Alternatives This is a CTSpedia version of an open access article originally published as: Bacchetti P. Curren...
Under Construction Significance Testing as Perverse Probabilistic ReasoningThis is a CTSpedia version of an open access article originally published as:Westover M...
Use of Significant Alone in Publications Do not use the word significant alone in scientific publications that include statistical analysis. This term is ambi...
Computer Assisted Interviewing Software Lead Editor(s): Main.NicolasSheon The two main reasons for using a computer to administer a survey are efficiency (no need...
Statistical Computing and Graphics Concepts to Master 1 Difference between a functional language with live access to data and a procedural or macro language ...
Common mistakes when describing a study population (the typical Table 1) Reports of both observational and experimental studies typically include descriptive summ...
Using a National Database Leading Author(s): Yolanda Hagar Helpful Tips, Hints and Things to Consider Using a national database can be very advantageous. The pri...