Monthly Archives: December 2014
Guest post by Pete Attkins
Commentator “jm” asked a profound and pertinent question: “What DOES it take for people to get real in this world, practice some common sense, and pay attention to what’s going on with themselves?” This question was asked in the context of asserting that personal experience always trumps the results of large-scale scientific experiments; and asserting that alt-med experts are better able to provide individulized healthcare than 21st Century orthodox medicine.
What does common sense and paying attention lead us to conclude about the following? We test a six-sided die for bias by rolling it 100 times. The number 1 occurs only once and the number 6 occurs many times, never on its own, but in several groups of consecutive sixes.
I think it is reasonable to say that common sense would, and should, lead everyone to conclude that the die is biased and not fit for its purpose as a source of random numbers.
In other words, we have a gut feeling that the die is untrustworthy. Gut instincts and common sense are geared towards maximizing our chances of survival in our complex and unpredictable world — these are innate and learnt behaviours that have enabled humans to survive despite the harshness of our ever changing habitat.
Only very recently in the long history of our species have we developed specialized tools that enable us to better understand our harsh and complex world: science and critical thinking. These tools are difficult to master because they still haven’t been incorporated into our primary and secondary formal education systems.
The vast majority of people do not have these skills therefore, when a scientific finding flies in the face of our gut instincts and/or common sense, it creates an overwhelming desire to reject the finding and classify the scientist(s) as being irrational and lacking basic common sense. It does not create an intense desire to accept the finding then painstakingly learn all of the science that went into producing the finding.
With that in mind, let’s rethink our common sense conclusion that the six-sided die is biased and untrustworthy. What we really mean is that the results have given all of us good reason to be highly suspicious of this die. We aren’t 100% certain that this die is biased, but our gut feeling and common sense are more than adequate to form a reasonable mistrust of it and to avoid using it for anything important to us. Reasons to keep this die rather than discard it might be to provide a source of mild entertainment or to use its bias for the purposes of cheating.
Some readers might be surprised to discover at this point that the results I presented from this apparently heavily-biased die are not only perfectly valid results obtained from a truly random unbiased die, they are to be fully expected. Even if the die had produced 100 sixes in that test, it would not confirm that the die is biased in any way whatsoever. Rolling a truly unbiased die once will produce one of six possible outcomes. Rolling the same die 100 times will produce one unique sequence out of the 6^100 (6.5 x 10^77) possible sequences: all of which are equally valid!
Gut feeling plus common sense rightfully informs us that the probability of a random die producing one hundred consecutive sixes is so incredibly remote that nobody will ever see it occur in reality. This conclusion is also mathematically sound: if there were 6.5 x 10^77 people on Earth, each performing the same test on truly random dice, there is no guarantee that anyone would observe a sequence of one hundred consecutive sixes.
When we observe a sequence such as 2 5 1 4 6 3 1 4 3 6 5 2… common sense informs us that the die is very likely random. If we calculate the arithmetic mean to be very close to 3.5 then common sense will lead us to conclude that the die is both random and unbiased enough to use it as a reliable source of random numbers.
Unfortunately, this is a perfect example of our gut feelings and common sense failing us abysmally. They totally failed to warn us that the 2 5 1 4 6 3 1 4 3 6 5 2… sequence we observed had exactly the same (im)probability of occurring as a sequence of one hundred 6s or any other sequence that one can think of that doesn’t look random to a human observer.
The 100-roll die test is nowhere near powerful enough to properly test a six-sided die, but this test is more than adequately powered to reveal some of our cognitive biases and some of the deficits in our personal mastery of science and critical thinking.
To properly test the die we need to provide solid evidence that it is both truly random and that its measured bias tends towards zero as the number of rolls tends towards infinity. We could use the services of one testing lab to conduct billions of test rolls, but this would not exclude errors caused by such things as miscalibrated equipment and experimenter bias. It is better to subdivide the testing across multiple labs then carefully analyse and appropriately aggregate the results: this dramatically reduces errors caused by equipment and humans.
In medicine, this testing process is performed via systematic reviews of multiple, independent, double-blind, placebo-controlled trials — every trial that is insufficiently powered to add meaningfully to the result is rightfully excluded from the aggregation.
Alt-med relies on a diametrically opposed testing process. It performs a plethora of only underpowered tests; presents those that just happen to show a positive result (just as a random die could’ve produced); and sweeps under the carpet the overwhelming number of tests that produced a negative result. It publishes only the ‘successes’, not its failures. By sweeping its failures under the carpet it feels justified in making the very bold claim: Our plethora of collected evidence shows clearly that it mostly ‘works’ and, when it doesn’t, it causes no harm.
One of the most acidic tests for a hypothesis and its supporting data (which is a mandatory test in a few branches of critical engineering) is to substitute the collected data for random data that has been carefully crafted to emulate the probability mass functions of the collected datasets. This test has to be run multiple times for reasons that I’ve attempted to explain in my random die example. If the proposer of the hypothesis is unable to explain the multiple failures resulting from this acid test then it is highly likely that the proposer either does not fully understand their hypothesis or that their hypothesis is indistinguishable from the null hypothesis.
Naturopathy can be defined as ‘an eclectic system of health care that uses elements of complementary and conventional medicine to support and enhance self-healing processes’. This basically means that naturopaths employ treatments based on those therapeutic options that are seen as natural, e. g. herbs, water, exercise, diet, fresh air, heat and cold – but occasionally also acupuncture, homeopathy and manual therapies. If you are tempted to see a naturopath, you might want to consider the following 7 points:
- In many countries, naturopathy is not a protected title; this means your naturopaths may have some training but this is not obligatory. Some medical doctors also practice naturopathy, and in some countries there are ‘doctors of naturopathy’ (these practitioners tend to see themselves as primary care physicians but they have not been to medical school).
- Naturopathy is steeped in the obsolete concept of vitalism which has been described as the belief that “living organisms are fundamentally different from non-living entities because they contain some non-physical element or are governed by different principles than are inanimate things.”
- While there is some evidence to suggest that some of the treatments used by naturopaths are effective for treating some conditions, this is by no means the case for all of the treatments in question.
- Naturopathy is implicitly based on the assumption that natural means safe. This notion is clearly wrong and misleading: not all the treatments used by naturopaths are strictly speaking natural, and very few are totally free of risks.
- Many naturopaths advise their patients against conventional treatments such as vaccines or antibiotics.
- Naturopaths tend to believe they can cure all or most diseases. Consequently many of the therapeutic claims for naturopathy found on the Internet and elsewhere are dangerously over-stated.
- The direct risks of naturopathy depend, of course, on the modality used; some of them can be considerable. The indirect risks of naturopathy can be even more serious and are mostly due to naturopathic treatments replacing more effective conventional therapies in cases of severe illness.
Aromatherapy is one of the most popular of all alternative therapies. It is most certainly a very agreeable experience. But is it more that a bit of pampering? Does it cure any diseases?
If you believe aromatherapists, their treatment is effective for almost everything. And, of course, there are studies to suggest that, indeed, it works for several conditions. But regular readers of this blog will by now know that it is a bad idea to go by just one single trial; we always must rely on the totality of the most reliable evidence. In other words, we must look for systematic reviews. Recently, such an article has been published.
The aim of this review was to systematically assess the effectiveness of aromatherapy for stress management. Seven databases were searched from their inception through April 2014. RCTs testing aromatherapy against any type of control intervention in healthy but stressed persons assessing stress and cortisol levels were considered. Two reviewers independently performed the selection of the studies, data abstraction and validations. The risk of bias was assessed using Cochrane criteria.
Five RCTs met the authors’ inclusion criteria. Most of the RCTs had high risk of bias. Four RCTs tested the effects of aroma inhalation compared with no treatment, no aroma, and no odour oil. The meta-analysis of these data suggested that aroma inhalation had favourable effects on stress management. Three RCTs tested aroma inhalation on saliva or serum cortisol level compared to controls, and the meta-analysis of these data failed to show significant difference between two groups
The authors concluded that there is limited evidence suggesting that aroma inhalation may be effective in controlling stress. However, the number, size and quality of the RCTs are too low to draw firm conclusions.
This is by no means the only systematic review of this area. In fact, there are so many that, in 2012, we decided to do an overview of systematic reviews evaluating the effectiveness of aromatherapy. We searched 12 electronic databases and our departmental files without restrictions of time or language. The methodological quality of all systematic reviews was evaluated independently by two authors. Of 201 potentially relevant publications, 10 met our inclusion criteria. Most of the systematic reviews were of poor methodological quality. The clinical subject areas were hypertension, depression, anxiety, pain relief, and dementia. For none of the conditions was the evidence convincing. Our conclusion: due to a number of caveats, the evidence is not sufficiently convincing that aromatherapy is an effective therapy for any condition.
So, what does all of this mean? I think it indicates that most of the claims made by aromatherapists are not evidence-based. Or, to express it differently: aromatherapy is hardly more than a bit of old-fashioned pampering – nothing wrong with that, of course, as long as you don’t fall for the hype of those who promote it.
Complementary treatments have become a popular (and ‘political correct’) option to keep desperate cancer patients happy. But how widely accepted is their use in oncology units? A brand-new article tried to find the answer to this question.
The principal aim of this survey was to map centres across Europe prioritizing those that provide public health services and operating within the national health system in integrative oncology (IO). A cross-sectional descriptive survey design was used to collect data. A questionnaire was elaborated concerning integrative oncology therapies to be administered to all the national health system oncology centres or hospitals in each European country. These institutes were identified by convenience sampling, searching on oncology websites and forums. The official websites of these structures were analysed to obtain more information about their activities and contacts.
Information was received from 123 (52.1 %) out of the 236 centres contacted until 31 December 2013. Forty-seven out of 99 responding centres meeting inclusion criteria (47.5 %) provided integrative oncology treatments, 24 from Italy and 23 from other European countries. The number of patients seen per year was on average 301.2 ± 337. Among the centres providing these kinds of therapies, 33 (70.2 %) use fixed protocols and 35 (74.5 %) use systems for the evaluation of results. Thirty-two centres (68.1 %) had research in progress or carried out until the deadline of the survey. The complementary and alternative medicines (CAMs) more frequently provided to cancer patients were acupuncture 26 (55.3 %), homeopathy 19 (40.4 %), herbal medicine 18 (38.3 %) and traditional Chinese medicine 17 (36.2 %); anthroposophic medicine 10 (21.3 %); homotoxicology 6 (12.8 %); and other therapies 30 (63.8 %). Treatments are mainly directed to reduce adverse reactions to chemo-radiotherapy (23.9 %), in particular nausea and vomiting (13.4 %) and leucopenia (5 %). The CAMs were also used to reduce pain and fatigue (10.9 %), to reduce side effects of iatrogenic menopause (8.8 %) and to improve anxiety and depression (5.9 %), gastrointestinal disorders (5 %), sleep disturbances and neuropathy (3.8 %).
As so often with surveys of this nature, the high non-response rate creates a problem: it is not unreasonable to assume that those centres that responded had an interest in IO, while those that failed to respond tended to have none. Thus the figures reported here for the usage of alternative therapies might be far higher than they actually are. One can only hope that this is the case. The idea that 40% of all cancer patients receive homeopathy, for instance, is hardly one that is in accordance with the principles of evidence-based practice.
The list of medical reasons for using largely unproven treatments is interesting, I think. I am not aware of lots of strong evidence to show that any of the treatments in question would generate more good than harm for any of the conditions in question.
What follows from all of this is worrying, in my view: thousands of desperate cancer patients are being duped into having bogus treatments paid for by their national health system. This, I think, begs the question whether these most vulnerable patients do not deserve better.
This investigation was aimed at examining the messages utilised by the chiropractic profession around issues of scope and efficacy through website communication with the public. For this purpose, the authors submitted the website content of 11 major Canadian chiropractic associations and colleges, and of 80 commercial clinics to a mixed-methods analysis. Content was reviewed to quantify specific health conditions described as treatable by chiropractic care. A qualitative textual analysis identified the primary messages related to evidence and efficacy utilised by the websites.
The results show that chiropractic was claimed to be capable of addressing a wide range of health issues. Quantitative analysis revealed that association and college websites identified a total of 41 unique conditions treatable by chiropractic, while private clinic websites named 159 distinct conditions. The most commonly cited conditions included back pain, headaches/migraines and neck pain. Qualitative analysis revealed three prominent themes drawn upon in discussions of efficacy and evidence: grounded in science, the conflation of safety and efficacy and “natural” healing.
The authors concluded that the chiropractic profession claims the capacity to treat health conditions that exceed those more traditionally associated with chiropractic. Website content persistently declared that such claims are supported by research and scientific evidence, and at times blurred the lines between safety and efficacy. The chiropractic profession may be struggling to define themselves both within the paradigm of conventional science as well as an alternative paradigm that embraces natural approaches.
These findings strike me as being similar to the ones we published 4 years ago. At this stage, we had conducted a review of 200 chiropractor websites and 9 chiropractic associations’ World Wide Web claims in Australia, Canada, New Zealand, the United Kingdom, and the United States. The outcome measures were claims (either direct or indirect) regarding the eight reviewed conditions, made in the context of chiropractic treatment: asthma, headache/migraine, infant colic, colic, ear infection/earache/otitis media, neck pain, whiplash (not supported by sound evidence), and lower back pain (supported by some evidence).
We found evidence that 190 (95%) chiropractor websites made unsubstantiated claims regarding at least one of the conditions. When colic and infant colic data were collapsed into one heading, there was evidence that 76 (38%) chiropractor websites made unsubstantiated claims about all the conditions not supported by sound evidence. Fifty-six (28%) websites and 4 of the 9 (44%) associations made claims about lower back pain, whereas 179 (90%) websites and all 9 associations made unsubstantiated claims about headache/migraine. Unsubstantiated claims were made about asthma, ear infection/earache/otitis media, neck pain.
At the time, we concluded that the majority of chiropractors and their associations in the English-speaking world seem to make therapeutic claims that are not supported by sound evidence, whilst only 28% of chiropractor websites promote lower back pain, which is supported by some evidence. We suggest the ubiquity of the unsubstantiated claims constitutes an ethical and public health issue.
Comparing the two studies, what should we conclude? Of course, the new investigation was confined to Canada; we therefore cannot generalise its results to other countries. Nevertheless it provides a fascinating insight into the (lack of) development of chiropractic in this part of the world. My conclusion is that, at least in Canada, there is very little evidence that chiropractic is about to become an ethical and evidence-based profession.
The purpose of this paper was to compare the characteristics of the chiropractic technique systems that have utilised radiography for subluxation detection with the characteristics of religion, and to discover potential historical links that may have facilitated the development of those characteristics.
The authors found 23 technique systems requiring radiography for subluxation analysis. Evidence of religiosity from the early founders’ writings was compared with textbooks, published papers, and websites of subsequently developed systems. Six criteria denoting religious thinking were developed: supernatural concepts, claims of supremacy, rules and rituals, sacred artefacts, sacred stories, and special language. All of these were found to a greater or lesser degree in the publicly available documents of all the subluxation-based chiropractic x-ray systems.
The authors concluded that the founders and early pioneers of chiropractic did not benefit from the current understanding of science and research, and therefore substituted deductive and inductive reasoning to arrive at conclusions about health and disease in the human body. Some of this thinking and rationalisation demonstrably followed a religion-like pattern, including BJ Palmer’s use of radiography. Although access to scientific methods and research education became much advanced and more accessible during the past few decades, the publicly available documents of technique systems that used radiography for chiropractic subluxation detection examined in this paper employed a historically derived paradigm for radiography that displayed characteristics in common with religion.
As I was pondering these amazing statements, a friend alerted me to the promotional material by a chiropractic college in the US. The website of this institution refers to subluxation – have we not been told that this term now belongs to the realm of chiropractic history? – in many places, e. g. :
Dr. Brian Kelly talks about the subluxation debate, and introduces to a comprehensive resource on the subluxation. Visit LifeWestPress to order your own copy of the “Atlas of Common Subluxations of the Human Spine and Pelvis.”
… an introduction to the literature concerning the scientific examination of the subluxation and its physiological and anatomical basis. The physiology, neurology, and biomechanics of subluxation and adjustment are surveyed.
The focus of Knee Chest Upper Cervical Chiropractic Care is to address the Upper Cervical Subluxation. This includes detecting the Subluxation, designing a customized correction with the assistance of imaging, and patient management.
Atlas of Common Subluxations By William J Ruch, D.C. “One of the most significant chiropractic clinical text of the decade” -Dr. Deed Harrison D.C. The serious results of subluxations of the spine can now been seen in color. by studying the dramatic consequences of chronic
Gonstead B provides an emphasis on patients who present with subluxations of the cervical and thoracic areas of the spine. Some case management protocols are also discussed. This course includes instruction in static and motion visualization, inspection, and palpation; skin temperature…
The president of this college tells us that “….We believe chiropractic is a vital part of health care and that the chiropractic lifestyle is something that the public is placing in high demand right now…” (Dr. Brian Kelly President). Inspired by such big words, I study more of the promotional material furthermore which informs us that:
We must study and understand the reason why chiropractic holds an impactful and necessary place in the future of our entire planet’s health. We must truly understand and own the principles of safe and e ective healthcare for all. Philosophy is not just “for fun”. Philosophy is the glue that holds all of the elements of our educational process together.
At this stage I begin to wonder whether they have more to offer than ‘philosophy’ – how about some evidence? I looked and looked hard, but my efforts were in vain. Evidence does not seem to be a focus of this college. Instead we are offered obsolete concepts like vitalism:
Vitalism is the understanding that there is more to the basic function of the human body than just a bunch of parts and mechanisms. There is something more to us than just many parts of a machine. Vitalism is the study of the underlying elements of the organization of intelligence in the human body (and in any living system) and how that intelligence runs the system. From a vitalistic viewpoint, the care provided by a chiropractor takes on a unique and critical role in supporting the human body’s natural inclination to heal itself and to remain healthy over the course of a lifetime.
Now I am acutely reminded of the well-documented fact that DD Palmer, the man who invented chiropractic, had toyed with the idea of founding a religion. Perhaps he has done exactly that and we have not yet noticed? More importantly perhaps, I get the feeling that all this talk (on this blog and elsewhere) that chiropractors are working ever so hard to leave their bizarre past behind and join the rest of us in the 21st century is little more that wishful thinking.
Adults using unproven treatments is one thing; if kids do it because they are told to, that is quite another thing. Children are in many ways more vulnerable than grown-ups and they usually cannot give fully informed consent. It follows that the use of such treatments for kids can be a delicate and complex matter.
A recent systematic review was aimed at summarizes the international findings for prevalence and predictors of complementary and alternative medicine (CAM) use among children/adolescents. The authors systematically searched 4 electronic databases (PubMed, Embase, PsycINFO, AMED; last update in 07/2013) and reference lists of existing reviews and all included studies. Publications without language restriction reporting patterns of CAM utilization among children/adolescents without chronic conditions were selected for inclusion. The prevalence rates for overall CAM use, homeopathy, and herbal drug use were extracted with a focus on country and recall period (lifetime, 1 year, current use). As predictors, the authors extracted socioeconomic factors, child‘s age, and gender.
Fifty-eight studies from 19 countries could be included in the review. There were strong variations regarding study quality. Prevalence rates for overall CAM use ranged from 10.9 – 87.6 % for lifetime use, and from 8 – 48.5 % for current use. The respective percentages for homeopathy (highest in Germany, United Kingdom, and Canada) ranged from 0.8 – 39 % (lifetime) and from 1 – 14.3 % (current). Herbal drug use (highest in Germany, Turkey, and Brazil) was reported for 0.8 – 85.5 % (lifetime) and 2.2 – 8.9 % (current) of the children/adolescents. Studies provided a relatively uniform picture of the predictors of overall CAM use: higher parental income and education, older children. But only a few studies analyzed predictors for single CAM modalities.
The authors drew the following conclusion: CAM use is widespread among children/adolescents. Prevalence rates vary widely regarding CAM modality, country, and reported recall period.
In 1999, I published a very similar review; at the time, I found just 10 studies. Their results suggested that the prevalence of CAM use by kids was variable but generally high. CAM was often perceived as helpful. Insufficient data existed about safety and cost. Today, the body of surveys monitoring CAM use by children seems to have grown almost six-fold, and the conclusions are still more or less the same – but have we made progress in answering the most pressing questions? Do we know whether all these CAM treatments generate more good than harm for children?
Swiss authors recently published a review of Cochrane reviews which might help answering these important questions. They performed a synthesis of all Cochrane reviews published between 1995 and 2012 in paediatrics that assessed the efficacy, and clinical implications and limitations of CAM use in children. Main outcome variables were: percentage of reviews that concluded that a certain intervention provides a benefit, percentage of reviews that concluded that a certain intervention should not be performed, and percentage of studies that concluded that the current level of evidence is inconclusive.
A total of 135 reviews were included – most from the United Kingdom (29/135), Australia (24/135) and China (24/135). Only 5/135 (3.7%) reviews gave a recommendation in favour of a certain intervention; 26/135 (19.4%) issued a conditional positive recommendation, and 9/135 (6.6%) reviews concluded that certain interventions should not be performed. Ninety-five reviews (70.3%) were inconclusive. The proportion of inconclusive reviews increased during three, a priori-defined, time intervals (1995-2000: 15/27 [55.6%]; 2001-2006: 33/44 [75%]; and 2007-2012: 47/64 [73.4%]). The three most common criticisms of the quality of the studies included were: more research needed (82/135), low methodological quality (57/135) and small number of study participants (48/135).
The Swiss authors concluded that given the disproportionate number of inconclusive reviews, there is an ongoing need for high quality research to assess the potential role of CAM in children. Unless the study of CAM is performed to the same science-based standards as conventional therapies, CAM therapies risk being perpetually marginalised by mainstream medicine.
And what about the risks?
To determine the types of adverse events associated with the use of CAM that come to the attention of Australian paediatricians. Australian researchers conducted a monthly active surveillance study of CAM-associated adverse events as reported to the Australian Paediatric Surveillance Unit between January 2001 and December 2003. They found 39 reports of adverse events associated with CAM use, including four reported deaths. Reports highlighted several areas of concern, including the risks associated with failure to use conventional medicine, the risks related to medication changes made by CAM practitioners and the significant dangers of dietary restriction. The reported deaths were associated with a failure to use conventional medicine in favour of a CAM therapy.
These authors concluded that CAM use has the potential to cause significant morbidity and fatal adverse outcomes. The diversity of CAM therapies and their associated adverse events demonstrate the difficulty addressing this area and the importance of establishing mechanisms by which adverse effects may be reported or monitored.
So, we know that lots of children are using CAMs because their parents want them to. We also know that most of the CAMs used for childhood conditions are not based on sound evidence. The crucial question is: can we be sure that CAM for kids generates more good than harm? I fear the answer is a clear and worrying NO.
Getting good and experienced lecturers for courses is not easy. Having someone who has done more research than most working in the field and who is internationally known, might therefore be a thrill for students and an image-boosting experience of colleges. In the true Christmas spirit, I am today making the offer of being of assistance to the many struggling educational institutions of alternative medicine .
A few days ago, I tweeted about my willingness to give free lectures to homeopathic colleges (so far without response). Having thought about it a bit, I would now like to extend this offer. I would be happy to give a free lecture to the students of any educational institution of alternative medicine. I suggest to
- do a general lecture on the clinical evidence of the 4 major types of alternative medicine (acupuncture, chiropractic, herbal medicine, homeopathy) or
- give a more specific lecture with in-depth analyses of any given alternative therapy.
I imagine that most of the institutions in question might be a bit anxious about such an idea, but there is no need to worry: I guarantee that everything I say will be strictly and transparently evidence-based. I will disclose my sources and am willing to make my presentation available to students so that they can read up the finer details about the evidence later at home. In other words, I will do my very best to only transmit the truth about the subject at hand.
Nobody wants to hire a lecturer without having at least a rough outline of what he will be talking about – fair enough! Here I present a short summary of the lecture as I envisage it:
- I will start by providing a background about myself, my qualifications and my experience in researching and lecturing on the matter at hand.
- This will be followed by a background on the therapies in question, their history, current use etc.
- Next I would elaborate on the main assumptions of the therapies in question and on their biological plausibility.
- This will be followed by a review of the claims made for the therapies in question.
- The main section of my lecture would be to review the clinical evidence regarding the efficacy of therapies in question. In doing this, I will not cherry-pick my evidence but rely, whenever possible, on authoritative systematic reviews, preferably those from the Cochrane Collaboration.
- This, of course, needs to be supplemented by a review of safety issues.
- If wanted, I could also say a few words about the importance of the placebo effect.
- I also suggest to discuss some of the most pertinent ethical issues.
- Finally, I would hope to arrive at a few clear conclusions.
You see, all is entirely up to scratch!
Perhaps you have some doubts about my abilities to lecture? I can assure you, I have done this sort of thing all my life, I have been a professor at three different universities, and I will probably manage a lecture to your students.
A final issue might be the costs involved. As I said, I would charge neither for the preparation (this can take several days depending on the exact topic), nor for the lecture itself. All I would hope for is that you refund my travel (and, if necessary over-night) expenses. And please note: this is time-limited: approaches will be accepted until 1 January 2015 for lectures any time during 2015.
I can assure you, this is a generous offer that you ought to consider seriously – unless, of course, you do not want your students to learn the truth!
(In which case, one would need to wonder why not)
