Primer of statistics in dental research: Part II.

The Part I of Primer of Statistics in Dental Research covered five topics that are often mentioned in statistical check list of many peer-review journals including (1) statistical graph, (2) how to deal with outliers, (3) p-value and confidence interval, (4) testing equivalence, and (5) multiplicity Adjustment. The Part II of the series covers another set of important topics in dental statistics including (1) selecting the proper statistical tests, (2) repeated measures analysis, (3) epidemiological consideration for causal association, and (4) analysis of agreement. First, a guide in selecting the proper statistical tests based on the research question will be laid out in text and with a table so that researchers choose the univariable statistical test by answering five simple questions. Second, the importance of utilizing repeated measures analysis will be illustrated. This is a key component of data analysis as in many dental studies, observations are considered repeated in a single patient (several teeth are measured in a single patient). Third, concepts of confounding and the use of regression analysis are explained by going over a famous observational cohort study. Lastly, the use of proper agreement analysis vs. correlation for study of agreement will be discussed to avoid a common pitfall in dental research.