Why did we have to go and make tea so complicated?
There is scientific method to our madness. We’ve been looking at the public’s beliefs about how tea should be made, and their actual abilities to distinguish different brews.
As scientists, we know that the most effective way to get reliable information is to design a method of systematic measurement. When systematic measurements are combined with interesting comparisons we have a scientific experiment.
There is an art to designing good experiments. We hope that the tea taste test has tested your beliefs and abilities whilst illustrating some essential principles of experimental design which are used by all scientists.
The scales of science
The key to the tea taste test and all modern experiments is the use of a branch of mathematics called statistics. The tea taste test was used as an example by one of the founding fathers of modern statistics, Ronald Fisher.
Fisher taught us that if we can create groups that are different from each other in just one respect (for example, milk first or tea first) then we can use simple mathematics to compare the groups. Any difference can then be clearly attributed to the single thing that is different between the two groups.
Put your money where your mouth is
If you dropped a kilogram weight off the top of your house and at exactly the same time a friend dropped a ten kilogram weight, which one do you think would land first?
We might have all sorts of good reasons for answering this question one way or the other but if we really want to know, at some point we have to try it out and take some measurements. Measurements are at the heart of science. Rather than making assumptions about what is true, we’re investigating people’s beliefs and abilities by making measurements. In this case it is a simple test: can you tell us which cup has milk in first out of a choice of two?
And the winner is...
No matter how respectable our tea tasters looked, we couldn’t tell them which type of tea they were tasting. We had to be sure that their decision was based on taste alone. If this was all we had done to prevent cheating our experiment would be described as single-blind but we were much craftier than that.
It has been shown that experimenters can inadvertently change the results of an experiment by affecting the choices made by participants. In order to avoid this problem, the person providing you with the cups of tea was also ignorant as to which cup was ‘milk first’ and which was ‘tea first’; our experiment was therefore double-blind.
Imagine if we had given everyone the milk-first tea in a cup with a picture of kittens on it and the tea-first tea in a cup with a picture of houseflies on it. How would we know whether the tea preference was based on when the milk was added or whether you had drunk out of the horrible fly cup?
Admittedly having cups with different pictures on is a pretty obvious mistake but there are loads of other things we had to take into account in order to run this experiment under controlled conditions. For example, we always used the same brands of milk and tea, the tea was always the same temperature, with the same milk to tea ratio, etc. By going to these lengths we have attempted to ensure that the only difference for all participants was whether milk was added first or last.
Milk-first first or tea-first first?
Our prediction is that people won’t be able to tell the difference between the two drinks. However, given the similarity of the tea in each cup it is possible that people will make a choice based on something irrelevant like ‘the cup on the right’. If everyone did this and we always put milk-first tea on the right we would think that everyone prefers tea with milk added first! To avoid problems like this, we have used a technique known as counterbalancing whereby we change the order in which the cups are presented for each person doing the test. If we’ve done this properly, in the end we should have an equal number of people who have tasted milk-first first and tea-first first.
Scientists prefer Clark Kent to Superman
If we had wanted to (and were persuasive enough), we could have stayed inside our department and invited a bunch of expert wine tasters, chefs and food critics to take part in our tea experiment. Maybe these people could use their expert taste buds to taste differences that most people wouldn’t notice. But this just wouldn’t have made us happy scientists.
The problem is that we would have no idea how the rest of the population would react and so no idea about whether people in general can tell the difference between the two cups of tea. Choosing who to test in an experiment is known as the sampling choice.
We used a sampling method known as opportunity sampling. In other words, we used participants that were conveniently available in the hope that, on average, the people drinking the tea are fairly typical of the general population. Sampling is extremely important in science and the sample we choose depends on what it is we want to find out. Sometimes we might want to test only women, sometimes children, sometimes cancer patients but in this case we wanted to test the Great British public!