# R notes for Activity 22-1: Close Friends

## 22-1 i. Computing the test statistic

You can use R to compute the test statistic. Recall that this test statistic has the form

```(x1bar - x2bar)/sqrt(s1*s1/n1 + s2*s2/n2)
```

You can fill in the values.

## 22-1 o. Computing a confidence interval

Okay, you need to compute

```(xfbar-xfbar) +/- tkstar*sqrt(sf*sf/nf + sm*sm/nm)
```

I'll leave you to fill in the details.

## 22-1 p. Computing the p-value

As the book suggests, you can use the applet. You can also use R's `pt` function to compute the p-value. Since it's a two-sided test, we should double the computed value.

```t = (1.861-2.089)/sqrt(1.777*1.777/654 + 1.760*1.760/813)
2*pt(t, df=653)
```

Samuel A. Rebelsky, rebelsky@grinnell.edu

Copyright (c) 2007-8 Samuel A. Rebelsky.

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