36.3 Example 2: Reading research

Consider this Abstract (Groves 2010):

Objective To determine whether the author’s 20.9 lb (9.5 kg) carbon frame bicycle reduced commuting time compared with his 29.75 lb (13.5 kg) steel frame bicycle.

Design Randomised trial.

Setting Sheffield and Chesterfield, United Kingdom, between mid-January 2010 and mid-July 2010.

Participants One consultant in anaesthesia and intensive care.

Main outcome measure Total time to complete the 27 mile (43.5 kilometre) journey from Sheffield to Chesterfield Royal Hospital and back.

Results The total distance travelled on the steel frame bicycle during the study period was 809 miles (1302 km) and on the carbon frame bicycle was 711 miles (1144 km). The difference in the mean journey time between the steel and carbon bicycles was 00:00:32 (hr:min:sec; 95% CI -00:03:34 to 00:02:30; \(P=0.72\)).

Conclusions A lighter bicycle did not lead to a detectable difference in commuting time. Cyclists may find it more cost effective to reduce their own weight rather than to purchase a lighter bicycle.

Groves (2010), p. 341

Based on this Abstract, again we can learn many things about the study.

  1. Ask the question: The POCI elements are:

    • Population: The trips by this rider, on his bikes, on his route to work. This is not easy to identify, but notice that there are many examples of this rider, on his bikes, on his route. For example, there are not many examples of different bikes, different riders, or different routes.
    • Outcome: ‘Total time to complete the 27 mile (43.5 kilometre) journey.’
    • Comparison: Between the steel-frame and carbon-frame bicycles.
    • Intervention: Yes, because the elements of the population (the different commutes) can be randomly allocated to be taken with the steel- or carbon-frame bikes.
  2. Design the study: The study is ‘randomised controlled trial,’ a type of experimental study. Random allocation has been used.

  3. Collect the data: The Abstract gives no information.

  4. Describe and summarise the data: The Abstract gives no summary data for each bike, but summarises the difference between the means: 32 seconds (95% CI between -3:34 and 2:30 minutes, but which bike produces the faster mean time is not stated).

  5. Analyse the data: Though not stated, probably a two-sample \(t\)-test.

  6. Report the results: ‘A lighter bicycle did not lead to a detectable difference in commuting time’: There is no evidence that the carbon-frame bicycle reduced the commmuting time (for this rider, on his route to work, with his bikes…). In any case, the difference between the two mean commuting times is 32 seconds… over a 43.5 kilometre journey: Hardly of any practical importance (Sect. 28.8)!

The RQ may be:

For trips made by one cyclist (on his bikes, on his route to work), is the mean time to complete the 43.5 kilometre the same for the steel-frame and carbon-frame bicycles?

This is a poor RQ: it is not relevant or interesting (Sect. 2.6) to anyone except this single rider: The results are relevant to one person in the entire world…

Another thing to observe: The RQ is one-tailed (does the carbon frame bicycle reduce commuting time), but the conclusion gives a two-tailed \(P\)-value. (This may not be obvious, but a one-tailed \(P\)-value cannot be larger than 0.5.)

This is a strange study… However, it appeared in a Christmas edition of BMJ, which contains more ‘light-hearted’ articles:

While the subject matter may be more light-hearted, research papers in the Christmas issue adhere to the same high standards of novelty, methodological rigour, reporting transparency, and readability as apply in the regular issue.

— From https://www.bmj.com/about-bmj/resources-authors/article-types/christmas-issue


Groves J. Bicycle weight and commuting time: Randomised trial. British Medical Journal. 2010;341.