Statistics How To

Statistics Definitions > Geodesy is the study of the size and shape of the Earth (or any planet), its magnetic field, topology, and orientation in space. It is a branch of earth science and applied mathematics, and makes use of statistical methods. Geodesy is also known as geodetics, geodetics engineering or geodetic engineering. Geodesy Models … Read more

Combinatorics> In combinatorics, the Stirling numbers of the second kind tell us how many ways there are of dividing up a set of n objects (all different, or at least all labeled) into k nonempty subsets. The k subsets aren’t labeled. We write Stirling numbers of the second kind as S(n,k) or: . Examples of … Read more

Probability Distributions > Weibull Distribution and Analysis Contents: What is the Weibull distribution? Weibull PDFs The Weibull family Weibull Analysis What is the Weibull Distribution? The Weibull distribution is a continuous probability distribution named after Swedish mathematician Waloddi Weibull. He originally proposed the distribution as a model for material breaking strength, but recognized the potential … Read more

Regression Analysis > A semiparametric model is a regression model with both a finite- and an infinite-dimensional component. A finite-dimensional component is spanned by some list of vectors (a vector is an object that has both magnitude and direction). The two-dimensional and three-dimensional spaces we deal with in everyday geometry are examples of finite-dimensional spaces, … Read more

Design of Experiments > Adaptive design clinical trial What is an Adaptive Design Clinical Trial? An adaptive design clinical trial (also called adaptive randomization) is any design that allows adaptations to a clinical trial as it progresses. This type of trial is strongly recommended by the FDA for several reasons, including that it increases the … Read more

Find a Range in Statistics > The range rule of thumb is a handy method of estimating the range from the standard deviation. It tells us that the range is generally about four times the standard deviation. So if your standard deviation is 2, you might guess that your range is about eight. Using the … Read more

Statistics Definitions > Sensitivity analysis is post-hoc analysis which tells us how robust our results are. It can give specific information on: Which assumptions are important, and how much they affect research results, How changes in methods, models, or the values of unmeasured variables affect results. Sensitivity analysis is also known as “what-if” analysis; It … Read more

RCTs > Effect modification happens when a particular variable has separate, different exposure effects depending on another variable. One way of looking at this is by thinking of your test pool as having subgroups, or strata; Effect modification happens when an exposure or treatment has a different effect and leads to a different outcome among … Read more

Survey Sampling > A kish grid is a way of randomly choosing household survey respondents. The method avoids selection bias, which is usually a result of not using the correct procedures to choose your participants. If you visit houses and survey the first person to answer the door, your results are probably going to be … Read more

Regression Analysis > Forward selection is a type of stepwise regression which begins with an empty model and adds in variables one by one. In each forward step, you add the one variable that gives the single best improvement to your model. It is one of two commonly used methods of stepwise regression; the other … Read more