Statistics How To

Sampling > Effective Sample Size What is an Effective Sample Size? An effective sample size (sometimes called an adequate sample size) in a study is one that will find a statistically significant effect for a scientifically significant event. In other words, an effective sample size ensures that an important research question gets answered correctly. In … Read more

Hypothesis Testing > What is the The Cochran-Mantel-Haenszel Test? The Cochran-Mantel-Haenszel (CMH) Test is a test of association for data from different sources, or from stratified data from one source. It is a generalization of the McNemar test, suitable for any experimental design including case control studies and prospective studies. While the McNemar can only … Read more

Logistic Regression > Hosmer-Lemeshow Test You may find it helpful to read this article first: What is Logistic Regression? What is the Hosmer-Lemeshow Test? The Hosmer-Lemeshow test (HL test) is a goodness of fit test for logistic regression, especially for risk prediction models. A goodness of fit test tells you how well your data fits … Read more

ROC Curve > C-Statistic You may want to read this article first: What is a Receiver Operating Characteristic (ROC) curve?. What is a C-Statistic? The C-statistic (sometimes called the “concordance” statistic or C-index) is a measure of goodness of fit for binary outcomes in a logistic regression model. In clinical studies, the C-statistic gives the … Read more

Statistics Definitions > Receiver Operating Characteristic (ROC) Curve What is a Receiver Operating Characteristic (ROC) Curve? A Receiver Operating Characteristic (ROC) Curve is a way to compare diagnostic tests. It is a plot of the true positive rate against the false positive rate.* A ROC plot shows: The relationship between sensitivity and specificity. For example, … Read more

Correlation Coefficients > Moran’s I What is Moran’s I? Moran’s I is a correlation coefficient that measures the overall spatial autocorrelation of your data set. In other words, it measures how one object is similar to others surrounding it. If objects are attracted (or repelled) by each other, it means that the observations are not … Read more

Statistics Definitions > Correlogram / Auto Correlation Function ACF Plot / Autocorrelation plot What is a Correlogram? A correlogram (also called Auto Correlation Function ACF Plot or Autocorrelation plot) is a visual way to show serial correlation in data that changes over time (i.e. time series data). Serial correlation (also called autocorrelation) is where an … Read more

Non Parametric Tests > Mann Kendall Trend Test What is the Mann Kendall Trend Test? The Mann Kendall Trend Test (sometimes called the M-K test) is used to analyze data collected over time for consistently increasing or decreasing trends (monotonic) in Y values. It is a non-parametric test, which means it works for all distributions … Read more

Design of Experiments > Retrospective Study Contents: Retrospective Study Terminology Note Advantages and Disadvantages Study Steps Retrospective Cohort Study Definition Types of Retrospective Cohort Study Retrospective Case-Control Retrospective Case Series Retrospective longitudinal study 1. What is a Retrospective Study? A retrospective study is an observational study that enrolls participants who already have a disease or … Read more

Design of Experiments > Case-Control Study What is a Case-Control Study? A case-control study is a retrospective study that looks back in time to find the relative risk between a specific exposure (e.g. second hand tobacco smoke) and an outcome (e.g. cancer). A control group of people who do not have the disease or who … Read more