Tag Archives: Research

Why does science so often seem to disagree with itself?? Thoughts for new scientists or non-scientists.

An undergraduate student of mine recently showed me a scientific journal article he had been reading that confused him. Specifically, one result of the paper was that people who ate a vegetarian diet had higher cancer rates than those who ate meat [1]. He was confused by this because he said he had read other papers that suggested the exact opposite [for example 2, 3]. The point of this post is not to get into any discussions about the health effects of meat, but rather to briefly discuss the implications of contradictory results from the scientific literature. There are three issues that are immediately relevant and fairly straightforward for a growing scientist or a non-scientist: variation in how studies are carried out, the ‘random sample’-based idea of science, and reproduction of research.

Perhaps the simplest of these is the idea that if you ask the same question in different ways, you might find different results. I would personally explain this by pointing out that how you ask the question actually changes the question itself, just a little bit. To illustrate this, start with the question, “Does eating meat increase your risk of cancer?” To test this, one might start with a group of people who eat the average omnivorous American diet, remove all meat from their diets, and compare their cancer rates to the control (meat-eating) group five years later. This study has in fact modified the question slightly and asked, “How does removing meat from an omnivorous diet affect cancer risk?” Alternatively, if you compare cancer rates in the general population between vegetarians and omnivores, you are asking, “How do cancer rates compare among people who eat vegetarian diets compared to those who eat omnivorous?” At first glance, this may seem a pedantic distinction, but in practice this difference can be major. Can you think of any reasons people might not eat meat that could affect their health in other ways? What about people who have a major family history of cancer? They might be very careful about what they eat, but might also have an elevated risk of cancer even if they take special care.

The second issue here is the ‘random sample’-based idea of science. In essence, scientists are trying to make general conclusions that are generalizable to all people, not just those in their current study. In order to do that, they often try to collect a sample of people that is representative of the entire population. If they fail to do that, it’s not strictly a flaw in study, but it becomes important to be clear about which populations the results can be generalized to. For example, imagine the only vegetarians I can find for a research study are part of specific religions such as Buddhists or Seventh-day Adventists, along with a smattering of upper-middle class white Lutherans, pretty common in my part of the country. Well, in the end, that’s a pretty limited sample of people. What else might those populations do differently than the general population?

Finally, science is based upon the idea of repeating the same study many times. Both due to the random sample idea, but also the way we do statistics to come to conclusions, there is a certain possibility of error to every study. A well-designed and well-conducted study with a fairly large sample size, carried out by objective researchers who have no financial stake in the outcome, should have a low possibility of simply being ‘wrong.’ Unfortunately, every individual study does have this possibility. Studies in which the researchers have a heavily vested interest, or that are carried out by people who are not careful and objective, may have a higher likelihood of making errors. Now, this may seem depressing: “Why should we even believe science?” Nevertheless, the true power of science arises in reproducibility. If ten different researchers have conducted the exact same research, and nine reach the same conclusions, you can be pretty confident in the results of the nine. To, be clear, the contradictory study may be of very high quality as well, and may simply have found a different result due to random chance.

So, when you read a study, and you find the results confusing, or contradictory to your prior beliefs, here is my suggestion. First, keep an open mind. Maybe your prior beliefs were wrong! Approach every new idea considering the possibility that it might be right. Second, think critically about the study. The authors have probably stated a research question or hypothesis. But ask yourself, is their stated question really the question they asked with their research? What population do they say they studied? Did they really? Finally, look for more. Do they cite other related research? What did that prior research conclude? Has any new research cited the paper in question? Try using Google Scholar, or any number of other search tools to find other research on the same topic. Look for a review! Some articles are actually just summaries of many other research articles, and can be enormously helpful in this situation. Maybe yours is the only relevant research, but maybe there is a large body of science either supporting it, or failing to. Happy sciencing!

 

References

  1. Burkert, N.T., et al., Nutrition and Health – The Association between Eating Behavior and Various Health Parameters: A Matched Sample Study. PLoS ONE, 2014. 9(2): p. e88278.
  2. Tantamango-Bartley, Y., et al., Vegetarian Diets and the Incidence of Cancer in a Low-risk Population. Cancer Epidemiology Biomarkers & Prevention, 2013. 22(2): p. 286-294.
  3. Key, T.J., et al., Cancer incidence in vegetarians: results from the European Prospective Investigation into Cancer and Nutrition (EPIC-Oxford). The American Journal of Clinical Nutrition, 2009. 89(5): p. 1620S-1626S.

 

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Winter is coming and the basics of trade-offs in biology

Winter is coming and the basics of trade-offs in biology

Butterfly season is over and it’s getting cold out, although I did just see a cabbage white flapping around erratically when I was walking to work this morning. Despite the troubles we had early on in the summer with butterflies dying, we did manage to collect some good data. More importantly, I think that we worked most of the kinks out of our experimental design so next year should go much smoother. Now that I have the time, I’m going to sit down and try to explain my research project, and why I am doing it. The explanation will take 3 posts, so I can take my time explaining the concepts to interested folks who are not biologists.

One of the basic concepts underlying my research is that of a trade-off. A trade-off occurs when an organism wants to do two different things, but has a limited amount of some important resource. The resource could be time, calories, vital nutrients, or many other things. A simple example from everyday life would be trying to buy both a television and a bike with a limited amount of money. You can’t afford an expensive television AND an expensive bike. Instead, you have to choose between a cheap television and an expensive bike, a cheap bike and an expensive television, or a moderately priced bike and a moderately priced television. You would ideally want both an expensive bike and an expensive television, but you are limited by a resource: money.

Trade-offs in biology work similarly, but often the mechanism or the resource are not fully understood. This would be like seeing someone with a cheap bike and an expensive television, but not knowing WHY they have a cheap bike. You can guess that they have a cheap bike because they have limited money and want a nice television more than they want a nice bike, but you can’t know for sure. To biologists, this often takes the form of the observation that species rarely exhibit ‘perfect’ combinations of traits that are evolutionarily important, such as lifespan and reproductive rate. Some species, such as elephants, are very long lived, but reproduce very slowly (see Figure 1). Other species, such as mice, reproduce extremely rapidly, but are also short-lived. Slow reproduction with a short lifespan is clearly not a good strategy, and should generally not evolve. Conversely, an ideal combination from an evolutionary perspective would be to live a very long time and also have lots of kids really fast*.  Nevertheless, this is rarely seen in nature. Biologists generally agree that this pattern means that there is some cost to reproducing rapidly, and therefore species that reproduce rapidly will not live as long. There are many other examples of traits that are similar involved in trade-offs, such as brain size, muscle strength, and growth rate. Essentially, any trait that is important in fitness but requires some limited resource will likely exhibit trade-offs.

Reproduction and lifespan tradeoff more detail

The same patterns are generally seen within species as well, but individual trade-offs are often less consistent within species than they are among species. The specific ecological considerations of individual species may play a role, or it may be because there is simply more extreme variation among species compared to within species. In other species, some individuals may simply have access to more resources than others, meaning that despite the potential for a trade-off if resources are spread evenly across individuals, no trade-off is apparent due to inequalities among individuals. Someone who makes more money than you gets to have both an expensive television AND an expensive bike, avoiding the trade-off. In my next post I will talk about how hormones influence traits within species, and then finally I will bring together the ideas I’ve presented within the larger framework of my current research.

*There are some persuasive, but more complex considerations that I’m not covering here – for example in some cases longer-lived species may benefit disproportionately from intensive parental care, which may itself trade off with offspring number. However, the idea of a trade-off being responsible is widely accepted, and therefore I will not discuss these other possibilities further.