4.6 Optional: Using the calculator statistics mode

(Answers are available in Sect. A.4)

Batteries are expensive, so comparing the performance of expensive and cheap batteries is helpful.

A test on the lifetime of batteries (Lindström 2011) compared the time for two brands of 1.5 volt batteries to reduce their voltage to 1.0 volts under standard testing conditions.

The times (in hours) for nine Energizer Max batteries and nine ALDI brand batteries (Ultracell) are shown in Table 4.1.

TABLE 4.1: The times taken for batteries to go from 1.5 volts to 1.0 volts, in hours)
Energizer 7.58 7.46 7.46 7.59 7.46 7.52 6.83 6.89 7.45
Ultracell 7.5 7.48 7.47 7.48 7.48 7.41 7.47 6.96 7.48
  1. The type of research study is Justify your answer.
  2. What are the units of observation and units of analysis?
  3. Use your calculator’s Statistics mode to compute the following. (Check your answers to ensure you are using your calculator correctly.)
    1. Compute the mean of the Energizer batteries (to two decimal places):
    2. Compute the standard deviation of the Energizer batteries (to three decimal places):
    3. Compute the mean of the Ultracell batteries (to two decimal places):
    4. Compute the standard deviation of the Ultracell batteries (to three decimal places):
  4. Explain what these calculations tells you.
  5. Compute the median lifetime for each brand, explain what this tells you. (Many calculators cannot compute medians.)
    1. Compute the median of the Energizer batteries (to two decimal places):
    2. Compute the median of the Ultracell batteries (to two decimal places):
  6. Determine (and justify) if the mean or median would be a more appropriate measure of centre for these data.
  7. Do you think evidence exists that the average time for the batteries to reach 1.0 volts is the same for each brand? Explain.
  8. Decide if outliers exist in the data. Explain. If so, identify them.
  9. Explain whether the cost of the batteries would also be important information to know. (See below.)
  10. What advice would you give about buying batteries based on these data?

The cost of the batteries, at the time of publication (05 September 2012), was:

  • Ultracell: A four-pack cost $2.49 from ALDI online
  • Energizer Max: A four-pack cost $5.97 from Woolworths online, on special; the normal price was $8.01 for the four-pack.

References

Lindström, Per. 2011. “Test Report for Primary Battery Testing for ALDI Stores Australia.” Intertek.