91Ó°ÊÓ

A study published in 2010 showed that city dwellers have a \(21 \%\) higher risk of developing anxiety disorders and a \(39 \%\) higher risk of developing mood disorders than those who live in the country. A follow-up study published in 2011 used brain scans of city dwellers and country dwellers as they took a difficult math test. \(^{46}\) To increase the stress of the participants, those conducting the study tried to humiliate the participants by telling them how poorly they were doing on the test. The brain scans showed very different levels of activity in stress centers of the brain, with the urban dwellers having greater brain activity than rural dwellers in areas that react to stress. (a) Is the 2010 study an experiment or an observational study? (b) Can we conclude from the 2010 study that living in a city increases a person's likelihood of developing an anxiety disorder or mood disorder? (c) Is the 2011 study an experiment or an observational study? (d) In the 2011 study, what is the explanatory variable and what is the response variable? Indicate whether each is categorical or quantitative. (e) Can we conclude from the 2011 study that living in a city increases activity in stress centers of the brain when a person is under stress?

Step by step solution

01

Identifying Types of Study

For the 2010 study, since the researchers didn't manipulate any variable and only observed the likelihood of developing disorders among city and country dwellers, this study is an observational study. The follow-up study in 2011 qualifies as an Experiment, as the researchers manipulated the conditions by giving a math test and scrutinizing participants. This stress-inducing situation qualifies as a controlled condition or treatment, hence making it an experiment.

02

Causality Determination

From the 2010 observational study, we cannot conclude causality, that is, living in a city does not necessarily cause a higher risk of developing an anxiety or mood disorder. In observational studies, hidden or unknown variables can be responsible for the increased risk. It could be that city dwellers have lifestyles or characteristics that make them more prone to these health issues, the city living itself might not be the direct factor.

03

Variable Identification & Categorization

In the 2011 experiment, the explanatory variable (independent variable) is the 'place of living' as it is the factor being manipulated (city vs country) and it is categorical. The response variable (dependent variable) is the 'level of brain activity' and it is quantitative as it's a measurable activity.

04

Causality Determination

From the 2011 study, since it's an experiment where the factor (place of living) was manipulated, causal conclusion could be drawn if results supported it. In this case, it seems to suggest that living in a city increases activity in stress centers of the brain when a person is under stress, indicating city living might have a causal role in brain's response to stress. However, further studies are needed to confirm this, considering multiple factors in real-world scenarios.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Observational Study

An observational study, as the name indicates, involves observing subjects in a natural setting without any manipulation of variables. Researchers gather data, make comparisons, and look for trends or associations.

For example, the 2010 study mentioned in the exercise collected data on the prevalence of anxiety and mood disorders among city and rural dwellers. The researchers conducted no intervention; they simply recorded what occurred organically in each environment. This type of study is valuable for identifying patterns and generating hypotheses, but it comes with constraints. It does not control for all the possible confounding factors, so determining a cause-and-effect relationship from an observational study alone is not reliable.

Experimental Study

In contrast to an observational study, an experimental study involves deliberate manipulation of variables to measure effects. The goal is to establish cause-and-effect relationships. In the 2011 study, the environment of the participants (urban vs rural) was the factor being manipulated, while their stress levels, determined by brain activity, were measured.

Experiments can be more powerful than observational studies in determining causality because the investigator controls the exposure of interest. This means that they can rule out or control for external factors that may influence the outcome, unlike in observational studies.

Causal Relationship

A causal relationship indicates that one event is the result of the occurrence of another event; there is a cause and effect. In the context of statistical studies, proving causation is complex and requires a careful experimental design to rule out possible confounding factors.

For the 2010 study mentioned, we could observe an association between city living and increased anxiety or mood disorders, but we cannot confidently claim that living in the city is the cause of these disorders without further controlled experimental data. The possibility of other variables influencing the outcome cannot be eliminated.

Explanatory Variable

An explanatory variable, also known as the independent variable, is what is manipulated during an experiment to observe how it affects the response variable. It’s the presumed cause.

In the 2011 study, the place of living (city vs country) served as the explanatory variable. It is categorical because living environments can be divided into distinct categories without any inherent numerical value. This allows researchers to examine the effects of different environments on stress levels systematically.

Response Variable

The response variable, or dependent variable, is the outcome of interest that researchers measure in a study. It’s the effect or presumed effect in the causal relationship.

In the 2011 experimental study, the brain activity levels during a stress-inducing task were the response variable. Researchers measured this variable quantitatively using brain scans, allowing for a numerical comparison of stress levels between urban and rural participants.