Once upon a time, a group of disheartened scientists found their tearoom bereft of teaspoons. Despite dispatching a research assistant to go purchase more – so sugar could be stirred and coffee dispensed – the newly purchased teaspoons disappeared within a few short months.
Exasperated by the disappearance, the scientists decided they would measure the phenomenon. Do the teaspoons really disappear over time?
The answer was a resounding yes: spoons in research institute tearooms seem to have legs. While good fun, the research is a good example of a study design referred to as “longitudinal”.
What is a longitudinal study?
A longitudinal study uses continuous or repeated measures to follow particular individuals – in this case, teaspoons – over prolonged periods of time.
The studies are generally observational in nature: the scientists simply watch and collect data over time. Typically, no external influence is applied during the course of the study.
Beyond just working out where all the teaspoons have gone, this study type is also useful for evaluating the relationship between risk factors and the development of disease (for example, heart disease), and the outcomes of treatments over different lengths of time.
In this study, the main questions posed by our researchers were to determine the overall rate of loss of teaspoons, and to work out how long it took for teaspoons to go missing.
They purchased 70 teaspoons (16 of which were of higher quality), each one discretely numbered and then distributed throughout the institute. Counts of the teaspoons were carried out weekly for two months, then fortnightly for a further three months. Desktops and other immediately visible surfaces were also scanned for “misplaced” spoons.
After five months of covert research, the study was revealed to the institute, and staff were asked to return or anonymously report any marked teaspoons which may have found their way into desk draws or homes.
Good study design
This type of data collection provides a simple example of what makes a good longitudinal study.
If we break it down, a longitudinal study needs to:
- take place over a prolonged period (this study was done over 5 months)
- be observational in nature (teaspoons were observed and counted, there was no intervention)
- conducted without external influences (teaspoon users/thieves were not aware they were being studied until the conclusion of the study itself).
What did the data say?
The results show that 56 (80 per cent) of the 70 teaspoons disappeared during the study, and that the half life of the teaspoons was 81 days (that is, half had disappeared permanently after that time).
The study also showed the half life of teaspoons in communal tearooms (42 days) was significantly shorter than for those in research group specific tearooms (77 days). The rate of loss was not influenced by the teaspoons’ value.