4.1 Introduction

Two independent sample \(t\)-tests are used to compare the means of two separate groups.

Consider the face-plant data (Wojcik et al. 1999) used in the textbook (Table 4.1).

The data file (forwardfall.csv) can be downloaded in Sect. 10.

You can download the data, and follow the instructions.

TABLE 4.1: Lean-forward angles for older and younger women
Younger women		Older women

29	34	18
32	27	15
34	32	23
31	28	13
33	27	12

References

Wojcik, Laura A., Darryl G. Thelen, Albert B. Schultz, James A. Ashton-Miller, and Neil B. Alexander. 1999. “Age and Gender Differences in Single-Step Recovery from a Forward Fall.” Journal of Gerentology 54A (1): M44–50.