Common cents

---

Please read the general guidelines first!

---

---

Objective

Evaluate the performance of the bus timetable

---

Materials

• Accurate watch
• Bus timetable
• Pen and paper for recording data

---

Methods

• Select one or more bus services which you intend to monitor.
• Use the bus timetable to identify the expected arrival time of the bus.
• Wait at the bus stop and record the actual arrival time (when wheels stop moving) of the bus.
• Convert the actual arrival time into number of seconds (or minutes) late (arrival before the scheduled time should be recorded as a negative number).
• record your observations over a 2 week period.

---

Analysis

• For each bus service monitored, draw a histogram of seconds late across the two week period (you may like to draw another histogram showing all observations combined across all bus services). Each histogram should be drawn on the same scale on the x and y axis to allow visual comparison.
• If the histograms are generally symmetric:
  • Calculate the mean and standard deviation of seconds late across all two weeks.
• If the histograms are generally skewed:
  • Calculate the median and inter-quartile range of seconds late across all two weeks.

---

Discussion

• Is there any sampling bias in your study? (Are the bus services you selected typical of all bus services or did you only focus on a particular type of service, such as school routes? Were the days on which you ran your study normal days?)
• Is there any measurement bias in your study? (Did you follow identical methods on each day? Was the watch correctly set and accurate? Did you miss any measurements? Were any services cancelled?)
• Based on your observations, do you believe that buses run late? If so, by how much?
• Based on your observations, do you believe that there are differences in lateness between bus services? If so, how much?
• What would you do to improve the study the next time you ran it?

BACK to projects page