An epidemiological task force conducted a two-year study across 50 regional hospital wards to evaluate the efficacy of newly installed continuous-discharge ultraviolet-C (UV-C) air disinfection units. During the study period, the incidence rate of hospital-acquired airborne respiratory infections in these 50 wards decreased by . Based on this observation, the hospital administration concluded that the installation of the UV-C units directly caused the reduction in airborne infection rates.
Match each logical role on the left with the statement on the right that best fulfills that role in evaluating the hospital administration's causal argument.
- Statement that identifies a confounding variable that weakens the causal conclusionSimultaneously with the UV-C system installation, all 50 participating wards implemented a mandatory high-frequency surface decontamination protocol.
- Statement that demonstrates a potential causal direction reversalHospital administration approved UV-C system deployment exclusively in response to wards experiencing severe infection spikes, which naturally motivated staff to increase clinical vigilance prior to system activation.
- Statement that serves as an assumption required by the administration's causal conclusionThe physical layout and primary mechanical ventilation rates of the participating hospital wards remained constant throughout the two-year study period.
- Statement that strengthens the causal conclusion by ruling out an alternative explanationInfection rates in non-participating control wards with similar patient demographics and baseline hygiene protocols did not decrease over the same two-year period.
Answer
The correct pairings match: (1) the confounding variable role with the statement regarding the simultaneous implementation of a mandatory surface decontamination protocol; (2) the causal direction reversal role with the statement regarding system deployment being triggered by prior infection spikes and staff vigilance; (3) the necessary assumption role with the statement that ventilation rates and physical layouts remained constant; and (4) the strengthening statement role with the observation that infection rates in non-participating control wards did not decrease.
The correct pairings accurately assign each logical role to its corresponding statement based on standard GMAT causal analysis principles. The co-occurring decontamination protocol serves as a confounding variable because it introduces an unmeasured alternative cause for lower infection rates. The deployment of UV-C units in response to prior infection spikes illustrates causal direction reversal by demonstrating that infection conditions triggered the intervention. The constancy of mechanical ventilation rates represents a required assumption because significant changes in ventilation would invalidate the claim that UV-C units were responsible. Finally, the lack of infection reduction in control wards strengthens the causal claim by demonstrating that the outcome does not occur in the absence of the intervention.
Step-by-Step Solution
Key Concept
Causal Reasoning in Two-Part Analysis: Confounding Factors, Reverse Causality, Necessary Assumptions, and Control Comparison