In: Math
A supermarket chain analyzed data on sales of a particular brand of snack cracker
at 104 stores for a certain one week period. The analyst decided to build a regresion model to predict the sales of the snack cracker based on the total sales of all brands in the snack cracker category.
f. Produce a 90% confidence prediction interval for the sales of the cracker
in a store where the category sales is 1005. Also produce the90 %
confidence prediction interval in a store where category sales is 900.
Can you with 90% confidence claim which store has higher cracker sales?
| CategorySales | Sales | 
| 1348 | 394 | 
| 1110 | 388 | 
| 1096 | 357 | 
| 1208 | 385 | 
| 1063 | 346 | 
| 1097 | 326 | 
| 1277 | 358 | 
| 1275 | 359 | 
| 1328 | 360 | 
| 1281 | 374 | 
| 1127 | 362 | 
| 1339 | 406 | 
| 1055 | 354 | 
| 1263 | 368 | 
| 1158 | 391 | 
| 1286 | 370 | 
| 1401 | 372 | 
| 1085 | 381 | 
| 1178 | 371 | 
| 1248 | 353 | 
| 1241 | 372 | 
| 1320 | 375 | 
| 1353 | 369 | 
| 1173 | 353 | 
| 1208 | 364 | 
| 1280 | 371 | 
| 1214 | 391 | 
| 1213 | 381 | 
| 1291 | 371 | 
| 1230 | 335 | 
| 1095 | 338 | 
| 1149 | 320 | 
| 1305 | 370 | 
| 1134 | 351 | 
| 1127 | 328 | 
| 1053 | 295 | 
| 1107 | 318 | 
| 1054 | 296 | 
| 1141 | 327 | 
| 1190 | 313 | 
| 1071 | 346 | 
| 1147 | 361 | 
| 1127 | 350 | 
| 1204 | 367 | 
| 1301 | 411 | 
| 1184 | 390 | 
| 1214 | 367 | 
| 1132 | 341 | 
| 1213 | 380 | 
| 1173 | 347 | 
| 1226 | 365 | 
| 1261 | 352 | 
| 1118 | 341 | 
| 1096 | 321 | 
| 1211 | 329 | 
| 1033 | 336 | 
| 1228 | 361 | 
| 1241 | 386 | 
| 1381 | 408 | 
| 1332 | 359 | 
| 1253 | 375 | 
| 1043 | 330 | 
| 1456 | 341 | 
| 1099 | 340 | 
| 1044 | 336 | 
| 1230 | 341 | 
| 1143 | 371 | 
| 1238 | 378 | 
| 1357 | 371 | 
| 1150 | 378 | 
| 1218 | 386 | 
| 1215 | 357 | 
| 1238 | 376 | 
| 1196 | 349 | 
| 1193 | 364 | 
| 1282 | 361 | 
| 1317 | 365 | 
| 1157 | 346 | 
| 1294 | 356 | 
| 1198 | 343 | 
| 1436 | 358 | 
| 1278 | 368 | 
| 1124 | 312 | 
| 1116 | 315 | 
| 1109 | 338 | 
| 1285 | 327 | 
| 1189 | 309 | 
| 1197 | 330 | 
| 1091 | 345 | 
| 1251 | 344 | 
| 1124 | 355 | 
| 1130 | 346 | 
| 1067 | 328 | 
| 1150 | 352 | 
| 1238 | 375 | 
| 1409 | 370 | 
| 1264 | 377 | 
| 1151 | 340 | 
| 1206 | 350 | 
| 1297 | 375 | 
| 1164 | 364 | 
| 1108 | 370 | 
| 1187 | 365 | 
| 1459 | 396 | 
I used Excel for fitting regression line.
Output:
| CategorySales (x) | Sales | (x- xbar)^2 | |||||||||||
| 1348 | 394 | 20380.418 | |||||||||||
| 1110 | 388 | 9070.6576 | SUMMARY OUTPUT | ||||||||||
| 1096 | 357 | 11933.378 | |||||||||||
| 1208 | 385 | 7.6176 | Regression Statistics | ||||||||||
| 1063 | 346 | 20232.218 | Multiple R | 0.517059 | |||||||||
| 1097 | 326 | 11715.898 | R Square | 0.26735 | |||||||||
| 1277 | 358 | 5149.4976 | Adjusted R Square | 0.260167 | |||||||||
| 1275 | 359 | 4866.4576 | Standard Error | 20.27043 | |||||||||
| 1328 | 360 | 15070.018 | Observations | 104 | |||||||||
| 1281 | 374 | 5739.5776 | |||||||||||
| 1127 | 362 | 6121.4976 | ANOVA | ||||||||||
| 1339 | 406 | 17891.738 | df | SS | MS | F | Significance F | ||||||
| 1055 | 354 | 22572.058 | Regression | 1 | 15293.63 | 15293.63 | 37.2207 | 1.91E-08 | |||||
| 1263 | 368 | 3336.2176 | Residual | 102 | 41910.83 | 410.8905 | |||||||
| 1158 | 391 | 2231.6176 | Total | 103 | 57204.46 | ||||||||
| 1286 | 370 | 6522.1776 | |||||||||||
| 1401 | 372 | 38321.978 | Coefficients | Standard Error | t Stat | P-value | Lower 95% | Upper 95% | Lower 95.0% | Upper 95.0% | |||
| 1085 | 381 | 14457.658 | Intercept | 205.7064 | 24.84049 | 8.281091 | 5E-13 | 156.4354 | 254.9774 | 156.4354 | 254.9774 | ||
| 1178 | 371 | 742.0176 | X Variable 1 | 0.125338 | 0.020544 | 6.100877 | 1.91E-08 | 0.084589 | 0.166088 | 0.084589 | 0.166088 | ||
| 1248 | 353 | 1828.4176 | |||||||||||
| 1241 | 372 | 1278.7776 | |||||||||||
| 1320 | 375 | 13169.858 | x bar = | 1205.24 | |||||||||
| 1353 | 369 | 21833.018 | sxx | 973515 | |||||||||
| 1173 | 353 | 1039.4176 | |||||||||||
| 1208 | 364 | 7.6176 | |||||||||||

