statistical software is that it contains modules for creating survey forms and collecting data. Epi

Info is available at https://www.cdc.gov/epiinfo/index.html.

Software for calculating sample size

Biostatisticians frequently encounter the problem of estimating sample size. The following are two

free applications we recommend for performing sample-size calculations:

G*Power: G*Power was developed at the Universität Düsseldorf and is used to estimate the

sample size for many different types of tests. Throughout this book, when we discuss sample-size

calculations, we give you advice on how to do them using G*Power. G*Power is available at

www.psychologie.hhu.de/arbeitsgruppen/allgemeine-psychologie-und-

arbeitspsychologie/gpower. To use the program, you download it from this website and install

it on your computer.

PS (Power and Sample Size Calculation): The PS program was developed by W.D. Dupont and

W.D. Plummer at Vanderbilt University. Like G*Power, you download the application from its

website and install it on your computer. The PS interface is similar to that of G*Power. PS is

available at https://biostat.app.vumc.org/wiki/Main/PowerSampleSize.

Choosing Between Code-based and Non–Code-

Based Methods

Most of the software mentioned up to this point in this chapter — including SAS, SPSS, R and Python

— use code files that can be saved and rerun on data at a later date. These programs run fundamentally

differently from programs such as Microsoft Excel, where you can run statistics on data, but no code

files are produced and saved. Also, when you use web-based calculators, specialized apps like

G*Power and PS for sample-size calculations, or online commercial platforms, no code files are

produced and saved.

This is an important issue in statistics. When no code files are produced or saved, you have no

record of the steps in your analysis. If you need to be able to reproduce your analysis, the only

way to be sure of this is to use software that allows you to save the code so you can run it again.

Storing Data in the Cloud

Cloud-based storage refers to storing large data files on a set of Internet servers designed specifically

for large data storage. Unlike old-fashioned stand-alone servers in server rooms, cloud-based servers

share storage space across the Internet, providing instantaneous access and back-up capabilities. If you

want to get rid of an old-fashioned server in your server room (that could be a SAS server), you will

have to contract with a cloud-based storage company to use its space for your data. Then, you will

have to find a way to move your data from your server into your new cloud storage. You will also have

to make sure you want to have a long-term relationship with this company, so you don’t have to move