#2 Common sense: when making comparisons, say, of two things, one of which must be presented as the standard or the norm so as to make the other appear different or abnormal. To illustrate this, let's imagine the scenario where a person would like to determine whether he/she has a fever. The person would simply have to measure his/her body temperature with a thermometer and compare it to 37°C, the approximate body temperature of a healthy human being. A temperature greater than 37°C is usually indicative of fever. Here "37°C” is the “standard” or “norm” that makes sense the measured body temperature of the individual. In other words, one cannot know that, for example, 39°C is an abnormally high body temperature without comparing it to 37°C.

The scientific mind: For researchers, when designing any experiment, it is of foremost importance to include a “standard” or, in scientific term, “control,” so that any data obtained from conducting the experiment can be analyzed against the “control.” For instance, to determine whether a cellular protein is activated or inhibited in response to external stimuli such as viral infection, one would want to have cell samples without or with the treatment of virus. The effect of virus on the behavior of the protein of interest can then determined by comparing the expression levels of the protein between the uninfected (control) cells and infected (experimental) cells. In reality, two controls should be used in this experiment. The first control sample consists of “untouched” cells that undergo no treatment. The second control sample should be “mock-infected” cells that are treated with only the buffer used to dilute the virus, hence the term “mock.” Now the experimental sample, as you probably have already figured out, contains cells infected with the virus, with the same volume as that of the buffer used in mock-infection. So why are there two controls? Simply, this is to ensure that the virus, not the buffer, is the effecting agent. You see, the first control is in fact the control for the second control, which in turn serves as the control for the experimental. The use of “double controls” adds stringency to the experiment and credibility to the resulting data. Assuming that our protein of interest is activated or up-regulated upon viral infection, then our data as presented in a bar graph might resemble what is shown at the upper-right corner of this entry.

We unconsciously yet frequently use "controls" in our daily-life "experiments." Just take notice of your thought processes when making comparative decisions; you might be amazed at how often your scientific mind is at work, even though you have never been trained for the lab bench.