The R `scan` function allows you to enter data without typing
commas. In the case below, the values were not actually typed but inserted
with cut and paste. The "24:" prompt means R has received 23
numbers and is waiting for the 24^{th}. Hit RETURN to cease data
entry. The data represent the speeds of cars measured in an area where the
speed limit is 30 miles per hour.

> speeds = scan() 1: 29 34 34 28 30 29 38 31 29 34 32 31 27 37 29 26 24 34 36 31 34 36 21 24: Read 23 items > stem(speeds) The decimal point is 1 digit(s) to the right of the | 2 | 14 2 | 6789999 3 | 0111244444 3 | 6678 > stem(speeds, scale=2) The decimal point is at the | 20 | 0 22 | 24 | 0 26 | 00 28 | 00000 30 | 0000 32 | 0 34 | 00000 36 | 000 38 | 0 > summary(speeds) Min. 1st Qu. Median Mean 3rd Qu. Max. 21.00 29.00 31.00 31.04 34.00 38.00 > t.test(speeds, mu=30, alternative="greater", conf.level=0.90) One Sample t-test data: speeds t = 1.1781, df = 22, p-value = 0.1257 alternative hypothesis: true mean is greater than 30 90 percent confidence interval: 29.87323 Inf sample estimates: mean of x 31.04348

Note that a single command returns both a hypothesis test and a
confidence interval. The confidence level must be specified as a number
between 0 and 1. Another alternative for `alternative` is "less".
Leaving it out gives a two-sided test/interval. The default mu is 0 and
the default confidence level 95%=0.95. Here we do not reject the null that
the average speed is equal to the speed limit. So, people do not appear to
be speeding *on average*. Left as an exercise is the possibly more
interesting question of what proportion *are* speeding.

© 2006 Robert W. Hayden