Daily no-shows and cancellations in 500-bed hotel
No-shows & late cancellations | ||||
---|---|---|---|---|
25 22 19 24 24 31 |
25 20 24 18 27 27 |
20 22 33 28 17 24 |
23 20 25 23 23 17 |
20 32 25 28 18 27 |
Tell students that statistics tries to extract useful information from variation.
Variation that can be understood in terms of other variables is explained variation and is signal.
The remaining unexplained variation is noise (though this natural variation may also be of interest in its own right).
In the first data set (hotel no-shows and cancellations), all variation is unexplained. No other information about the days is available (e.g. weather) that might help to explain the variability in the strengths.
The second data set is experimental and the treatment (lathe speed and type of cutting tool) explains most variation in surface finish.
The last data set is observational. Some variation in strength may be explained (understood) in terms of lifetime alcohol consumption.
Hotel no-shows and cancellations
In hotels, a proportion of people who reserve rooms never show up (called 'no-shows') or cancel at the last moment. Large hotels therefore overbook under the assumption that a proportion of these 'no-shows' and cancellations will free up space. The table shows numbers of no-shows and late cancellations in a 500-room hotel during a 30-day period when the hotel had over 90 percent occupancy.
Surface finish from lathe
A mechanical engineer is investigating the surface finish of metal parts produced on a lathe and its relationship to the speed (in RPM) of the lathe. Twenty parts were produced at different lathe speeds and using two different types of cutting tool (code numbers 302 and 416).
Alcoholism and strength
Data that were obtained from 50 alcoholic men who were selected from a larger group of alcoholics to be as similar as possible in age and social characteristics. The researchers estimated the total lifetime alcohol consumption (kg per kg body weight) of each individual and measured the strength of a muscle (kg) in that individual's non-dominant arm.