Statistics for Dental Clinicians

Michael Glick, DMD, FDS RCSEd, is Professor of Oral Medicine and Executive Director, Center for Integrative Global Oral Health in the School of Dental Medicine at the University of Pennsylvania in Philadelphia, Pennsylvania, USA.Alonso Carrasco-Labra, DDS, MSc, PhD, is an Associate Professor in the Department of Preventive & Restorative Sciences and Director, Cochrane Oral Health Collaborating Center at Penn Dental Medicine, Center for Integrative Global Oral Health in the School of Dental Medicine at the University of Pennsylvania in Philadelphia, Pennsylvania, USA.Olivia Urquhart, MPH, is an Instructor in the Department of Preventive & Restorative Sciences, Center for Integrative Global Oral Health in the School of Dental Medicine at the University of Pennsylvania in Philadelphia, Pennsylvania, USA.

• Preamble xi1 What is statistics and why do we need it? 1Selected readings 72 Understanding and interpreting measures of association 8Effect and effect size 8Dichotomous outcome variables 9Data presentation and interpretation 9Absolute risk 9Absolute risk difference 10Relative risk or risk ratio 10Odds ratio 11Mean difference 11A few additional notes 12Selected readings 163 Understanding and interpreting a standard deviation and normal distribution 17A few additional notes 22Selected readings 234 Understanding and interpreting standard error 24Interpretation of the standard error of the mean 25Implication of the standard error of the mean 26A few additional notes 26Selected readings 295 Understanding and interpreting hypothesis testing and p-values 30Descriptive and inferential statistics 30Sampling error 31Hypothesis testing or null hypothesis significance testing 31Null and alternative hypotheses 32Significance 33P-value 34A few additional notes 36Selected readings 376 Understanding and interpreting a confidence interval 38Understanding the confidence interval 39How to interpret a confidence interval 39A few additional notes 41Selected readings 447 Understanding and interpreting power analysis and sample size 45Sample size: Why is it important? 45Components of a sample size calculation 46Size of the effect 46Significance level and type I error 47Power and type II error 49A few additional notes 50Selected readings 538 Understanding and interpreting a survival analysis 54Kaplan-Meier or survival curve 55Comparing two Kaplan-Meier (survival) curves 57Cox proportional hazard model 58A few additional notes 59Selected readings 609 Understanding and interpreting a probabilistic-based diagnosis 61Sensitivity 61Specificity 63Positive predictive value 63Negative predictive value 63Likelihood ratios 65Selective readings 6810 Understanding and interpreting a correlation 69Pearson product-moment correlation 69Interpretation of Pearson correlation coefficients and coefficient of determination 71Misinterpretation of correlations 73A few additional notes 74Selected readings 7411 Understanding and interpreting a regression analysis 76Estimation 76Prediction 77Linear regression 77Multiple (or multivariable) linear (MLR) regression 79Logistic regression 79Predicting risk and odds 80A hypothetical example: predicting risk and odds of an outcome 80Estimating odds ratios 81A hypothetical example--estimating an odds ratio 81Nonindependence of observations 82Building a regression model 82A few additional notes 82Selected readings 8512 Understanding and interpreting confounding and effect modification 86Counterfactual framework and causal reasoning 86Causal inference and confounding bias 87Strategies to deal with confounding in the study design phase 891. Randomization 902. Specification 903. Matching 90Strategies to deal with confounding in the analysis phase 921. Stratification 922. Propensity score 923. Traditional regression modeling 93Effect modification 94A few additional notes 95Selected readings 9713 Understanding and interpreting bias 98Random error versus systematic error (bias) 98What does it really mean? 99Distinguishing risk of bias, methodological quality, and reporting quality 100Assessing risk of bias in primary studies 101A few additional notes 104Selected readings 10514 Understanding and interpreting patient-reported outcomes 106Identifying optimal patient-reported outcome measures 108Validity 108Reliability 109A hypothetical scenario--Cohen's kappa (k) 109Responsiveness 110A few additional notes 111Selected readings 11215 Understanding and interpreting a cross-sectional study 113Bias in cross-sectional studies 113Response rate and avoiding nonresponse 114Analysis of cross-sectional studies 115Advantages and limitations of a cross-sectional study 116A few additional notes 116Selected readings 11916 Understanding and interpreting a case-control study 120Selection of the study population 120Identifying cases 120Identifying controls 122Retrospective assessment of the exposure 122Strengths and limitations 124Selected readings 12517 Understanding and interpreting a cohort study 126Types of cohort study designs 126Selection of the study population 127Measuring exposures 128Measuring outcome frequency 129Measures of association 129Bias in cohort studies 130Selection bias 130Nonparticipation and nonresponse 130Loss to follow-up or attrition bias 130Information bias: Dissimilar information between exposed and unexposed participants 130Confounding 131Strengths and limitations 131Suggested readings 13218 Understanding and interpreting a randomized controlled trial 133Study arms 135Type of outcomes 135Methodological strategies in randomized controlled trials 137Nonadherence to study protocol 137Missing data 139Subgroup analysis or effect modification 140A few additional notes 142Selected readings 14419 Understanding and interpreting meta-analyses 145The value of meta-analysis 145Pairwise meta-analysis 146Fixed effect meta-analysis 146Random effects meta-analysis 147Weight of each study in a meta-analysis 147Forest plots 147Heterogeneity 149Network meta-analysis 151Sensitivity analysis 152Certainty of the evidence 152A few additional notes 153Selected readings 15420 Understanding and interpreting statistical and clinical significance 155A few additional notes 158Selected readings 158Appendix 1 Formulas and equations 160Appendix 2 Z-table 183Appendix 3 T-table 185Glossary 189Index 210