Ina 2014 study published by the American Academy of Neurology, Poor sleep quality is associated with increasedcortical atrophy in community-dwelling adults, researchers, Sexton et al., performeda correlational study to explore the relationship between level of sleep qualityand corresponding physical conditions of the body, specifically the brain. Bothcorrelational and experimental studies compare two variables. However, eventhough by correlational design, we can establish whether a relationship existsbetween two variables, we cannot determine the cause of that relationship becausethis design lacks the processes needed to establish the direction of therelationship, eliminate possible third variables, or tell which variable comesfirst.
Also, correlational studies employ grouping variables that are only usedto categorize observations and aid visualization, unlike those of an experiment.The conductors of this study, Sexton et al., 2014, do not implement manipulationor random assignment, two distinguished tools of an experimental design, to proposeany causal relationship between one’s standard of sleep quality and the physicalconditions of one’s brain. The researchers in this correlational study speculatedthat lower levels of sleep quality were associated with degeneration of sizeand function in certain regions of the human brain, such as several structures ofthe cortex. To conduct the study, the researchers used the Pittsburg SleepQuality Index to measure the sleep quality of community residents, varying inage and gender, and compared these levels to different features of the corticaland hippocampal areas of the brain, such as decay and cubic measure, obtained throughMRI scans.
They then performed several post hoc tests to analyze whether ageplayed a role in their findings, as well as to evaluate potential third-party influencessuch as body mass index (BMI,) blood pressure, and levels of physical movement.Only partially supporting the original hypothesis, the research findings displayedthat lower levels of sleep quality were longitudinally correlated with increasedrates of degeneration in cortical functions and decreased cortical cubic measure,with the exception of the hippocampus. These results were predominantly true ofrelationships within the group of participants over the age of sixty, and theaforementioned third-party variables did not prove to play a role in thefinding. The researchers also reiterate a key note of this study in theirconclusion: “Poor sleep quality may be a cause or consequence of brain atrophy,and future studies examining the effect of interventions that improve sleepquality on rates of atrophy may hold key insights into the direction of thisrelationship.” By including this statement, the researchers stress that thedesign of this particular study did not include the necessary measures forindicating any causal relationships between the variables that they compared, thoughan experimental study could.
Their findings strictly indicate association, notcausality. In her article, “Lack of Sleep MayShrink Your Brain,” the author, Val Willingham, cites findings from the abovestudy, Sexton et al., 2014, as well as a few other sources to discuss how sleepdeprivation affects the physical condition of the human brain. Despite theresearchers’ steady assertions that their research cannot evidence a causal relationshipbetween poor sleep quality and brain volume, the title that Willingham chosefor her article, which utilizes the outcomes of this study for credibility andevidence, is inappropriate and misleading because the it suggests order and directionin the relationship. Her title implicates that sleep quality influences brainsize, though the possibility remains that it could be the reverse. Order anddirection of a correlation can only be supported by experimentally-designedstudies, as these studies perform the sufficient measures to eliminate third-variableproblems and to observe the causal power of a certain variable. It continues,and Willingham begins her article by describing the design and outcome of the 2014study published by the American Academy of Neurology, specifically noting that thoseindividuals considered to have lower levels of sleep quality did also happen todisplay a greater decline in brain size throughout the study.
From here, Willinghaminserts information from other studies, such as sleep deprivation inducingbrain illnesses, to work towards her next statement: “So it stands to reasonthat, if a lack of sleep can lead to memory loss, the size of the brain wouldalso be affected.” Neither studies that the author draws information from directlysupport the relationship that the author asserts here. Instead, Willingham pullsfindings from both studies to draw her own conclusion about a causal relationshipbetween sleep quality and brain volume; this statement is therefore fallacious.
However, as the author continues, she contradicts her statement above and citesthe original, valid conclusions drawn in Sexton et al.,2014: the direction ofthe relationship between sleep quality and brain degeneration has yet to beestablished, and further research would need to be conducted to decipher whichvariable manipulates the other. Although Willingham closes her article with anaccurate report of the final conclusions from the study, she makes several statementsand conclusions throughout that imply a causal relationship, which cannot besupported by the study. After close evaluation of both articles,I conclude that, overall, Val Willingham does not provide readers with an entirelyaccurate report of the 2014 American Academy of Neurology study in her article,”Lack of sleep may shrink your brain.” In her report, Willingham is guilty offaulty reasoning; she utilizes information found in several studies to form herown conclusions about the effects of sleep on brain volume, that are notnecessarily supported by the findings in Sexton et al., 2014.
Willingham’s statementquoted above gives the illusion of credibility, when in fact the onlyrelationship actually evidenced is merely correlation, not causality. Though shedoes accurately relay information regarding the structure design of the study accurately,when discussing the results, the author’s language suggests causality. Asaforementioned, causal conclusions cannot be drawn from correlational studiesbecause these types of studies do not involve the additional measures, such asmanipulation of a variable and random assignment, required to establish causationalpower and direction. Manipulating or changing a variable allows us to observeits causal power and it eliminates the question of direction in therelationship. With random assignment, individual differences are averaged outbetween different groups, which dismisses the third-variable problem of notknowing if an outside variable is influencing the correlation between the twovariables being studied. An example of possible third-variable in the correlationbetween level of sleep quality and brain size could be