In this note, we discuss the use of Cohen’s D for planning difference-of-mean experiments.
Estimating sample size
Let’s imagine you are testing a new weight loss program and comparing it so some existing weight loss regimen. You want to run an experiment to determine if the new program is more effective than the old one. You’ll put a control group on the old plan, and a treatment group on the new plan, and after three months, you’ll measure how much weight the subjects lost, and see which plan does better on average.
Nina and I have been sending out drafts of our book Practical Data Science with R 2nd Edition for technical review. A few of the reviews came back from reviewers that described themselves with variations of:
Senior Business Analyst for COMPANYNAME. I have been involved in presenting graphs of data for many years.
To us this reads as somebody with deep experience, confidence, and bit of humility. They do something technical and valuable, but because they understand it they do not consider it to be arcane magic.
In this note we describe might can happen if such a person (or if a junior version of such a person) acquires 1 or 2 technical books.
We have just released two new free video lectures on vectors from a programmer’s point of view. I am experimenting with what ideas do programmers find interesting about vectors, what concepts do they consider safe starting points, and how to condense and present the material.
In this note we share a quick study timing how long it takes to perform some simple data manipulation tasks with Rdata.frames.
We are interested in the time needed to select a column, alter a column, or select a row. Knowing what is fast and what is slow is critical in planning code, so here we examine some common simple cases. It is often impractical to port large applications between different work-paradigms, so we use porting small tasks as approximate stand-ins for measuring porting whole systems.
We tend to work with medium size data (hundreds of columns and millions of rows in memory), so that is the scale we simulate and study.
In this note we will use five real life examples to demonstrate data layout transforms using the cdataR package. The examples for this note are all demo-examples from tidyr:demo/ (current when we shared this note on 2019-04-27, removed 2019-04-28), and are mostly based on questions posted to StackOverflow. They represent a good cross-section of data layout problems, so they are a good set of examples or exercises to work through.