The survival time of chocolates on hospital wards: covert observational studyBMJ 2013; 347 doi: https://doi.org/10.1136/bmj.f7198 (Published 14 December 2013) Cite this as: BMJ 2013;347:f7198
All rapid responses
Recently a study was published in this journal about the lifetimes of donated chocolates in a hospital environment . This study generated much interest. A Google internet search (assessed February 12, 2014) resulted in 986,000 hits using the search phrase “The survival time of chocolates on hospital wards". A critical note however about this study is in order. Because of debatable methods, statistics and results the conclusions of the study are subject to uncertainty.
a) To avoid potential contamination bias, we think the trial should better have been designed as a cluster randomized study .
b) The location and display of the two boxes containing the chocolate test products, Roses and Quality Street, in each of the four test areas is critical . Considering the heavy workload of many hospital employees it is likely that the box closest to the entrance door of the test facility will be emptied at the fastest rate. The locations of the boxes at each ward should have been determined using an appropriate randomization scheme.
c) The survival times of the chocolates were measured from the time the boxes were opened. This conflicts with the “intention-to-treat” principle. In our view the survival times should have been measured from the time that the chocolate boxes were placed in the test areas. This appears particularly important because there was a clear difference between the two test brands regarding the mean time until the boxes were opened (19 vs 5 min). This difference was reported to be not significant using the t-test, but absence of a proof of a difference should not be interpreted as a proof of absence of a difference .
d) In addition to the previous point, the 95% CI of the mean time until opening of all the 8 boxes used ranged from 0 to 24 minutes. From this it can be calculated that the SD of the opening times equals 14.4 minutes (=12 /2.365 times the square root of 8). This SD is larger than the reported mean value of 12 minutes, which shows that the opening times of the boxes did not follow a normal Gaussian distribution . Therefore the t-test used to compare the mean opening times of the boxes between the brands is not appropriate.
e) There were significant differences between the four investigated wards with regard to the effect size expressing the difference between the two brands, as can be seen from the non-overlapping confidence intervals of the reported separate hazard ratios. No explanation or discussion of these differences is given. Due to the observed heterogeneity of effects the findings are difficult to generalize.
f) The hazard ratio (Roses versus Quality Street) of the two chocolate brands for all wards combined was calculated to be 0.70. This number being less than 1 indicates that the Roses chocolates survived longer than the other brand. But this result contradicts the Kaplan-Meier curves shown which clearly demonstrate that the Roses chocolates survived a shorter time. This raises some questions. Was there perhaps any mislabeling of the test products in the computer database? Or did the data analist by mistake model the event “survival” of the chocolate instead of “death” in the Cox regression survival analysis? Was it verified whether the required proportional hazards assumption in the calculation of hazard ratios was fulfilled?
g) The primary outcome of the study was the median survival time of the chocolates, which was calculated to be 51 minutes. The shown Kaplan-Meier curves however suggest that the median value of the combined groups should be about 100 minutes. Using a well-fitting exponential decay curve the investigators further calculated that the survival half time was 99 minutes. This supports our suspicion that the reported median survival time of 51 minutes is inaccurate.
h) The “loss to follow-up” rate of the chocolates was high (26%). The main reason for this was that observers prematurely ended the continuous observation of the test boxes. This was a clear violation of the protocol which writes (supplementary web information, page 3): “The observers will record data until both chocolate boxes have emptied”. This suggests that the trial was executed in a suboptimal way. Was there any monitoring of the trial by independent qualified persons, especially regarding the conduct, including any chocolate consumption, of the observers?
The authors are complimented for their efforts to get a better understanding of the consumption of donated chocolates at the working place. But, with all respect, in view of some flaws and errors in the trial, we think reliable conclusions are not possible as yet. Further studies are needed.
 Gajendragadkar PR, Moualed DJ, Nicolson PLR, Adjei FD, Cakebread HE, Duehmke RM, Martin CA. The survival time of chocolates on hospital wards: covert observational study. BMJ 2013; 347:f7198.
 HundleyV, Cheyne H, Bland JM ,Styles M , Barnett CA. So you want to conduct a cluster randomized controlled trial? Journal of Evaluation in Clinical Practice 2010;16:632–638.
 Dijksterhuis A, Smith PK, Baaren RB van, Wigboldus DHJ. The unconscious consumer: effects of environment on consumer behavior. Journal of Consumer Psychology 2005;15:193-202.
 William Cowper (English poet, 1731-1800), quote: “Absence of proof is not proof of absence”.
 Blythe EK, Merhaut DJ. Testing the assumption of normality for pH and electrical conductivity of substrate extract obtained using the pour-through method. HortScience 2007;42:661-669.
Competing interests: No competing interests
Considering the declaration of interests, monetary and in the form of sandwiches, pies, etc currently being discussed, I am a little surprised that none of those consuming chocolates given by patients or friends/relatives of patients have assured us that the gifts were declared. Or, perhaps the recipients felt that these cariogenic and diabetogenic articles were gifts in the German language sense (gift, English= poison, German ). Or, Greeks bearing gifts?
Competing interests: No chocolates
I thank the authors for such an entertaining article and have equally enjoyed reading the responses.
Firstly as part of primary care we have an abundant supply of chocolates as well as biscuits, cakes all throughout the year. (In fact we will probably finish our current stock by Easter.)
My personal observations are that a standard box lasts usually < 2 days, whilst a large tin of either Roses, Quality Street or Celebrations tends to last about 3- 4 days amongst 13 staff/GPs. Usually it's the brown wrapped chocolates or toffees that are left forlornly at the bottom - while we wait patiently to open the next tin.
The most popular - blue coconut or Maltesers - are the first to disappear (usually I've eaten those - competing with our secretary). Fortunately I can't stand praline or toffee ones.
Patients tend to buy us fancy chocolate biscuits but most of us prefer plain ones.
When I first started General Practice in 1984 , I was a size 12-14 , but after sitting on my backside for nearly 30 yrs all day - just moving to to kitchen where the goodies are, I am now a size 18 ! (unless M&S sizing has changed ?)
Has anyone researched weight gain in General Practice primary care team staff compared to secondary care staff ?........
If the authors would like a guinea pig for a follow up chocolate study, I would only be too pleased to offer myself in the name of medical research......
Competing interests: Chocoholic
Like many mortals, we find that chocolate has a “kyryptonite”-like effect on our determination to lead a Spartan lifestyle. The occasional presence of chocolate gifts in the workplace is an occupational hazard.
As doctors with an interest in public health, we read Gajendragadkar et al’s paper on chocolate survival time in hospital with some interest.
We think the authors missed an opportunity to examine the potential link between regular chocolate consumption and weight gain. Although there is one passing reference to the possibility of chocolate-related weight gain in paragraph 9 under “Ethical Issues”, we fear the public health risks of regular chocolate consumption may have been underestimated at best, ignored at worst.
We would hypothesise that those with a higher BMI are prone to consuming more of these chocolates on the ward. There is evidence to support this hypothesis. A recent longitudinal study found that habitual chocolate consumption is linked to weight gain and higher BMI.
We feel this is a hypothesis that is ripe for testing. If our hypothesis is correct, NHS Trusts should revisit their health and wellbeing policies and consider rationing ward chocolates in the interest of staff health. This would be a worthy health promotion initiative which we would heartily support.
 Wikipedia: Kryptonite. http://en.wikipedia.org/wiki/Kryptonite
 Gajendragadkar P R et al. The survival time of chocolates on hospital wards: covert observational study. BMJ 2013;347:f7198
 Greenberg J A, Buljsse B. Habitual chocolate consumption may increase body weight in a dose-response manner. PLoS One 2013;8(8):e70271
Competing interests: GYS is not keen on either Quality Street or Cadbury’s Roses chocolates. He is partial to Maltesers. RJM is a fan of Quality Street. This letter represents the authors’ personal views, not those of their employer.
I realise, as a latecomer to the discussion, my comments may already been voiced by other readers but I see no evidence of this based on published rapid responses so far as they go.
As a responsible clinician and teacher, I must vigorously protest the misleading nature of the title of the paper as it is obvious to me (as to any self-respecting connoisseur of quality chocolate) that the researchers are not aware of the basic difference in the contents of study matter namely Quality Street and Roses product as sold in UK.
In spite of regional difference in the confectionery makeup of boxed product, I can declare with certainty the following facts:
1. In UK (as in the world), Quality Street products contains BOTH chocolate-based and toffee based sweets (12 varieties in total with about 25% toffee content).
2. Rose chocolate sweets (10 varieties in a box) in UK are all chocolate coated with only one sweet has toffee as the main content
3. 1 out of 12 Quality sweets uses dark chocolate, for Roses (in UK format) it is 1 out of 10.
4. The serving size for Quality Street sweets is 29g which account for 3 sweets.
5. Serving size for Rose sweets (UK) is 25g which is listed as 2 sweets.
6. As a result each sweet is estimated at 9.6g for Quality Street, 12.5g for Rose (UK).
Furthermore I would also point out in the usual work pattern in a surgical unit differs significantly from a medical-based ward care as follows:
1. Surgical ward round generally start earlier than medical round, as the surgeons will need to attend operating theatre and/or clinics which invariably start in normal local working hours.
2. Time exposed to doctors in ward for surgical unit is less than for medical units (as usually the surgical team is likely to complete their rounds in a shorter time).
3. The 10am start time for the study almost certainly means that for acute units (like surgical and acute medical ward) staff are involved in direct personal health care at that time (including cleaning/showering, clinical procedures like drain removals/ dressing changes etc)
This, without doubt, compromises the value of data as analysed by the authors. I shall list my concerns about their conclusions as followed:
1. The authors did not recognise the inherent difference in the content of the study products, that not all Quality Street sweet are chocolate cover and Quality Streets sweets does not contain as much chocolate as Rose.
2. Quality Street sweets come in smaller size as compared to Rose
3. Clearly the nursing and healthcare assistant cohort knew which product to consume as reflected by their obvious bias to Rose sweets (larger, higher chocolate content)
4. Comparison of the decay and half-life of each product clearly reflects the popularity of the Rose product
5. The authors fail to recognise the difference in consumption between wards as a result of the difference in workflow of units.
6. Australasian experience (unpublished data: 2000 – 2004, single surgical (28 bed) ward in a tertiary hospital, 6 months Jan –July observational study annually, 750g blocks of Cabrury™ and Nestle™ chocolate, 9.30 am start time per working weekday) suggest that it is an statistical impossibility for any chocolate to survive beyond 45 minute except for Easter and Christmas season.
In conclusion I submit that the title of the article is misleading and the authors had failed to account for the inherent self-selection bias in spite of the exploratory nature of the study.
Competing interests: I was a regular supplier of Chocolate to my ward staff in my younger days and only stopped the practice after an inadvertent episode of direct observation of ugly feeding frenzy by ward nurses, akin to both substance dependence and conditioned response.
As a member of my university's Institutional Review Board (IRB), I am concerned that the authors "did not seek ethical approval" for their study. Had an investigator proceeded with a similar study without IRB approval at my institution, they would certainly be chastised and likely also be required to perform some kind of remediation before being allowed to perform future research.
For all the reasons given by the authors (no subject-identifiable data, lack of coercion, minimal risk), the study protocol would certainly have been approved as Exempt from requiring informed consent. But the lack of even seeking approval is troubling to me, as it circumvents the primary purpose of ethical review, i.e. to ensure that research subjects' rights and safety are adequately protected.
I completely understand that no one was harmed here and that the Christmas issues of BMJ intentionally contain more light-hearted research and articles. Indeed, I wish that American medical journals would follow suit.
Competing interests: No competing interests
There is one unanswered question. Are any of the subgroups eating more than their fair share of the chocolates? For example, if physicians are only 10% of the hospital staff and they are eating 15% of the chocolate, then they are obviously eating more than their fair share of the chocolates.
Competing interests: Not infrequent consumer of chocolates when rounding
A Comment on "The survival time of chocolates on hospital wards: covert observational study"
David A. Pink, Research Professor, Physics Department, St.Francis Xavier University, Antigonish, NS, Canada Erzsebet, Papp-Szabo, Senior Research Associate, Physics Department, University of Guelph, Guelph, ON, Canada, Andras T. Papp, Junior Medical Officer, Joondalup Health Campus, Hollywood Private Hospital, Perth, WA, Australia
Recently Gajendragadkar et al.1 published a seminal study of the consumption of chocolates on hospital wards. Statistical analyses showed that (a) taken as a group, healthcare assistants and nurses were the largest consumers of chocolate, (b) overall, ward chocolate consumers preferred Roses chocolates compared with Quality Street chocolates and (c) an exponential decay model best explained the time course ofa box of chocolates being consumed in a ward environment. While observations (a) and (b) raise important questions, we would like to address observation (c) in light of the comment "The behavioural or anthropological basis of this model remains unclear and is in need of further investigation, although similar patterns are seen in a variety of biological processes."
It is worth noting that the exponential decay model was fitted to the total data and no analyses of the different categories of consumers were carried out. In this case, we can consider the observed exponential decay to be a quantity averaged over a range of consumers, and treat the case in which we have a large number of chocolates accessible to a large number of consumers. With this proviso we can consider the number of chocolates to be a continuous differentiable function of time. Accordingly, at the risk of stressing the obvious, we bring the following to the attention of readers.
Let us assume that the dynamics of consumption is dominated by parameters describing, for example, becoming satiated. To analyze the result of such a simple model, let us denote by C the number of chocolates initially accessible to consumers. We take this initial time, t, to be t=0. We denote by N(t) the total number of chocolates consumed in the time interval [0,t]. Let us suppose that the average effect of satiation at time t is proportional, on the average, to the number of chocolates consumed up to that time, C-N(t), and that its magnitude is defined by a coefficient of satiation, which we denote by S. A positive value of S means that the consumation rate of chocolates is, on the average, a decreasing quantity as time increases. Accordingly, we can write,
dN(t)⁄dt= S[C-N(t) ] (1)
The solution to this differential equation, with the initial condition that, when t=0, N(0)=0, is
N(t)= C[1-exp(-St) ] (2)
where exp(x) is the exponential function. The number of chocolates remaining at time t is
C-N(t)= Cexp(-St) (3)
This simple model accounts for the observed exponential decay of the data averaged over all chocolate consumers in the study and identifies a single parameter governing the dynamics, the coefficient of satiation, S. It is perhaps noteworthy that the value of S is strongly product-dependent: for Roses, S=0.0083 per min, whereas for Quality Street S=0.0050 per min. The success of this model does raise some possibly-interesting questions: is the value of S consumer occupation-dependent, and which external parameters might it depend upon, e.g. time of day, proximity to coffee-breaks and stress levels.
This work was unsupported by any granting agency or commercial interest. None of the authors have any connection to the chocolate industry. EP-S is a discerning chocolate consumer.
1 Gajendragadkar, P.R., Moualed, D.J., Nicolson, P.L.R., Adjei, F.D., Cakebread, H.E., Duehmke, R.M., Martin, C.A. The survival time of chocolates on hospital wards: covert observational study. BMJ 2013;347:f7198
Competing interests: No competing interests
I would be interested to know whether individuals eating the candy washed their hands directly before consuming it.
A Nurses' station is not a particularly clean area, especially when considering potential for contamination of keyboards and telephones.
Competing interests: I am paid to tell individuals providing medical care to wash their hands.
It was with great enthusiasm that I read your intriguing and very topical paper. However I was disappointed to note that there was no further exploration or discussion of 'other' staff observed to succumb to the chocolate consumption. In this respect I would suggest in further research that you need to look into the chocolate eating habits of dietitians. Known to all round the hospital as purveyors of healthy eating and sound nutritional advice I have to admit to knowing no other group of staff who can consume chocolate at such a rate!
Competing interests: No competing interests