The New York Times reported recently on a study suggesting that taking a walk can be beneficial.
The article reports on a study showing that taking a lunchtime walk improves workers' enthusiasm and relaxation at work. Along with five other researchers, Dr. Thøgersen-Ntoumani randomly assigned some physically inactive staff at a large university in England to walk three times a week for 30 minutes, while researchers asked those in the control condition not to change their typical exercise behavior. Prior research led researchers to hypothesize that those in the experimental (walk) condition would report greater well-being than those in the control condition.
Questions:
To introduce the topic, the journalist reports that
It is not news, of course, that walking is healthy and that people who walk or otherwise exercise regularly tend to be more calm, alert and happy than people who are inactive.
a) What kind of claim is this? What are the variables in the claim?
The Times goes on to report that
A new study finds that even gentle lunchtime strolls can perceptibly — and immediately — buoy people’s moods and ability to handle stress at work.
b) What type of claim is this? What are the variables in the claim?
The journalist also writes that
Most of the resulting 56 volunteers were middle-aged women. It can be difficult to attract men to join walking programs, said Cecilie Thogersen-Ntoumani, the study’s lead author and now a professor of exercise science at Curtin University in Perth, Australia. Walking may not strike some men as strenuous enough to bother with, she said. But she and her colleagues did attract four sedentary middle-aged men to the experiment.
c) What type of study validity does this statement concern?
For the first set of analyses, the NY Times goes on to report that
The volunteers completed a series of baseline health and fitness and mood tests at the outset of the experiment, revealing that they all were out of shape but otherwise generally healthy physically and emotionally. Dr. Thogersen-Ntoumani and her colleagues then randomly divided the volunteers into two groups, one of which was to begin a simple, 10-week walking program right away, while the other group would wait and start their walking program 10 weeks later, serving, in the meantime, as a control group.
d) Is participation in the walking program a between-subjects or within-subjects variable at this stage of the study? Why did the researchers use random assignment?
During the intervention period, the researchers also compared the responses to questions about mood given first thing in the morning to those given after the lunchtime walk by participants’ who were in the walking program, and they compared their responses after lunch on days they had walked with days they did not walk. As the Times reports,
On the afternoons after a lunchtime stroll, walkers said they felt considerably more enthusiastic, less tense, and generally more relaxed and able to cope than on afternoons when they hadn’t walked and even compared with their own moods from a morning before a walk.
e) After reading this description, you might have noticed that, in addition to their overall between subjects design, these researchers embedded a within groups design. What is the primary advantage of a within-groups comparison over a between-groups comparison?
f) Is the causal claim made by the Times (listed in question b) justified? Apply the three criteria.
Suggested answers:
a) This is an association claim, as the comparative wording (tend to be more …) suggests. The two measured variables are walking and emotional/mental state (degree of calmness, alertness, and happiness).
b) This is a causal claim, because the word buoys is a causal verb meaning "to increase" or "lift up." The variables are walking (IV) and mood and ability to handle stress (DVs).
c) This statement concerns the external validity of the study, as the sample was not randomly selected and is not representative of the population of sedentary office workers in terms of gender.
d) Participation in the walking program at the start of the study was a between-groups variable. Random assignment typically results in equivalent groups and rules out selection effects, such as individual differences among the participants. The use of random assignment means that participation in the walking program was a between-subjects variable.
e) The primary advantage of a within-groups comparison is that there are no subject variable confounds (selection effects), because the participants are the same in both groups (i.e., it is the same people completing the ratings in the morning before the walk and in the afternoon after the walk).
f) The study meets the three criteria for causality. There is covariance; that is, participants in the walking group gave higher mood ratings than those in the control condition. The IV, walking, took place prior to the participants’ giving their ratings of mood, establishing temporal precedence. Finally, the researchers used random assignment to address potential third variables, suggesting strong internal validity.
Warmest thanks to Chantal Poister Tusher, Lecturer at Georgia State University, for guest blogging today!