12.1 Opening Example
A student experimented to compare download speed at different times of the day. He placed a file on a remote server and then proceeded to download the file at three different periods of the day: 7 a.m., 5 p.m., and 12 a.m. He downloaded the file 48 times, 16 times at each period and recorded the download time in seconds (De Veaux, Velleman, & Bock, 2008). Does the data below provide sufficient evidence of a difference between the mean download time at 7 a.m., 5 p.m., and 12 a.m.?
Table 12.1: Download Time at 7 a.m., 5 p.m., and 12 a.m.
| Time of day | Time (sec) | Time of day | Time (sec) | Time of day | Time (sec) |
| 7 a.m. | 68 | 5 p.m. | 299 | 12 a.m. | 216 |
| 7 a.m. | 138 | 5 p.m. | 367 | 12 a.m. | 175 |
| 7 a.m. | 75 | 5 p.m. | 331 | 12 a.m. | 274 |
| 7 a.m. | 186 | 5 p.m. | 257 | 12 a.m. | 171 |
| 7 a.m. | 68 | 5 p.m. | 260 | 12 a.m. | 187 |
| 7 a.m. | 217 | 5 p.m. | 269 | 12 a.m. | 213 |
| 7 a.m. | 93 | 5 p.m. | 251 | 12 a.m. | 221 |
| 7 a.m. | 90 | 5 p.m. | 200 | 12 a.m. | 139 |
| 7 a.m. | 71 | 5 p.m. | 296 | 12 a.m. | 226 |
| 7 a.m. | 154 | 5 p.m. | 204 | 12 a.m. | 128 |
| 7 a.m. | 166 | 5 p.m. | 190 | 12 a.m. | 236 |
| 7 a.m. | 130 | 5 p.m. | 240 | 12 a.m. | 128 |
| 7 a.m. | 72 | 5 p.m. | 350 | 12 a.m. | 217 |
| 7 a.m. | 81 | 5 p.m. | 256 | 12 a.m. | 196 |
| 7 a.m. | 76 | 5 p.m. | 282 | 12 a.m. | 201 |
| 7 a.m. | 129 | 5 p.m. | 320 | 12 a.m. | 161 |
| [latex]\bar{x}_1=[/latex]113.375 | [latex]\bar{x}_2=[/latex]273.250 | [latex]\bar{x}_3=[/latex]193.063 |
