If you’ve ever smelled a baby’s head (I know....it can be irresistible!), you probably inhaled a variety of chemicals, including one called HEX.
A group of researchers recently published a study in which they exposed men and women to this particular chemical. They suggested that, given human evolutionary theory and emerging research on how different smells affect us, the smell of HEX might impact people's behavior. In the study, they focused on the behavior of aggression, using a laboratory game. The research was summarized by a journalist for the Voice of America.
The researchers’ hypotheses were derived from human evolutionary theory related to aggression:
…lead author Eva Mishor, who was studying signals of aggression for her doctorate at the Weizmann Institute, noted that in animals, female aggression is usually aimed at defending their young, while male aggression is often directed at the offspring themselves.
Specifically, the authors demonstrated that in a childrearing context, smelling HEX (the baby-head chemical) led to different responses in males than females.
The study tested people's responses to HEX using rigged games designed to aggravate the player. In one game, when the aggravated player is allowed to win, he or she gets to blast the opponent with a loud noise. The louder the noise, the higher the scientists rated the player's aggression level.
[Among players who] sniffed HEX before playing [compared to players who had sniffed a control chemical], women's blasts were louder and men's were quieter.
In case you didn't notice, this study used a 2x2 factorial design with an IV and a PV. Let’s walk through it.
a. What is the first factor (the independent variable?) What are its 2 levels? Was it manipulated as independent-groups or within groups?
b. What is the second factor (the participant variable?) What are its 2 levels? Was this variable independent groups or within groups?
c. What was the dependent variable?
d. Read the description of the results in the last quoted paragraph above. Then, sketch a little graph of the results they are describing (please assume that, in the non-HEX control condition, men are a bit more aggressive than women).
e. The results of the study show an interaction. Describe the interaction in your own words.
f. The journalist describes the results like so:
The effect was somewhat subtle. On a six-point scale, the differences were, on average, roughly between half a point and less than a point in either direction.
Here the journalist seems to be characterizing the effect size, and seems to be referring to the 95%CI of the difference. This is unique; most journalists do not mention the size of such effects or their CI.
Suggested answers:
a. The first factor was exposure to HEX (or not). This variable was manipulated as a between-groups variable—people played the aggression-inducing game either after smelling HEX OR after smelling a control (non-HEX) scent (i.e., there were different people in each condition).
b. The second factor was the participant variable of participant gender. It’s a participant variable because there are two levels (male and female) that cannot be truly manipulated. This is an independent-groups variable because people were either male or female.
c. The dependent variable was level of aggression, as operationalized as noise blasts.
d. Here's a sketch I made, based only on the journalist's description. You should look at the actual results in Figure 2 of the open-access article in Science Advances. Because the researchers also coded noise blast intensity over time, their results figure includes that factor as well.
