All practice questions

A 45-year-old man is brought to the emergency department after a propane tank explosion at his home. He is awake, alert, and complaining of severe pain. Physical examination reveals deep partial-thickness (second-degree) and full-thickness (third-degree) burns involving his entire posterior trunk and both of his entire upper extremities. There are also superficial (first-degree) burns involving his entire face and neck. The remainder of his body is unaffected. Based on the Rule of Nines, what is the estimated total body surface area (TBSA) percentage that should be used to calculate his initial fluid resuscitation requirements?

A 45-year-old woman is brought to the emergency department 30 minutes after being rescued from a residential fire. Her airway is patent, and she is hemodynamically stable. Physical examination reveals deep partial-thickness and full-thickness burns involving her entire anterior trunk, her entire right arm, and her entire right leg. Her estimated weight is $80 \text{ kg}$. Using the Parkland resuscitation formula ($4 \text{ mL/kg/} \% \text{TBSA}$), what should be the target rate of intravenous lactated Ringer solution administration, in $\text{mL/hour}$, for the first 8 hours following her injury?

A clinical study evaluates a novel prophylactic drug for episodic tension-type headaches among 200 adult participants over a 6-month period. Participants are equally divided into two groups. In the group receiving the standard placebo, 30 out of 100 participants experience a severe headache episode. In the group receiving the novel prophylactic drug, 10 out of 100 participants experience a severe headache episode. Based on these findings, what is the number needed to treat (NNT) to prevent one severe headache episode?

A randomized controlled trial is conducted to evaluate a new selective estrogen receptor modulator (SERM) for the prevention of breast cancer in high-risk postmenopausal women. The study enrolls 1,600 women, who are randomly assigned in a 1:1 ratio to receive either the new SERM or a placebo. The participants are followed for 5 years. During the follow-up period, 56 out of the 800 women receiving the new SERM develop deep vein thrombosis (DVT). In the placebo group, 16 out of the 800 women develop DVT.

Based on these study results, what is the number needed to harm (NNH) for DVT associated with this new SERM?

Investigators at a regional cardiovascular center analyze data from a prospective study evaluating a new oral anticoagulant compared to standard therapy for stroke prevention. The study followed patients with nonvalvular atrial fibrillation over a two-year period. Among the $1,000$ patients receiving the new anticoagulant, $20$ experienced an ischemic stroke. Among the $1,000$ patients receiving standard therapy, $70$ experienced an ischemic stroke. Based on these findings, what is the number needed to treat with the new anticoagulant to prevent one additional ischemic stroke compared to standard therapy?

Investigators are evaluating the efficacy of a newly developed long-acting monoclonal antibody for preventing severe respiratory syncytial virus (RSV) infections in high-risk premature infants. A total of $5,000$ infants are enrolled and randomized in a 1:1 ratio to receive either the monoclonal antibody or a placebo injection at the start of the RSV season. All participants are followed for $150$ days. At the end of the follow-up period, data analysis reveals that $50$ infants in the monoclonal antibody group and $150$ infants in the placebo group required hospitalization for severe RSV infection.

Based on these study results, what is the number needed to treat to prevent one RSV-related hospitalization?

A group of researchers is investigating a new serological assay for a tick-borne illness. They recruit $1,000$ subjects from an endemic region. All subjects undergo both the new serological assay and the gold-standard polymerase chain reaction (PCR) test.

The PCR test confirms that $100$ subjects have the illness.
Among these $100$ infected subjects, $90$ have a positive result on the new serological assay.
Among the $900$ subjects who test negative for the illness by PCR, $810$ test negative on the new serological assay, while $90$ test positive.

A $35$-year-old man from this region undergoes the new serological assay, and the result is positive. Based on the study results, what is the percentage probability that this man actually has the tick-borne illness?

A pharmaceutical company conducts a 3-year, randomized, double-blind, placebo-controlled trial to evaluate the efficacy of a novel medication in preventing the progression to end-stage renal disease (ESRD) in patients with type 2 diabetes and chronic kidney disease. A total of 3,000 patients are enrolled and randomly assigned in a 1:1 ratio to receive either the novel medication or a placebo. All patients complete the 3-year follow-up period. The study results are summarized in the following table:

Based on the information provided, how many patients must be treated with the novel medication for 3 years to prevent one additional case of end-stage renal disease compared to placebo?

A clinical study is conducted to evaluate a novel rapid diagnostic test for a specific bacterial infection. The study enrolls $1,000$ participants. A gold standard culture method confirms that $100$ participants currently have the infection. The novel rapid test returns a positive result for $90$ of the infected participants. Additionally, the rapid test returns a positive result for $30$ participants who do not have the infection. All other participants tested negative. What is the positive predictive value of this novel rapid diagnostic test, expressed as a percentage?

A gastroenterology research team is evaluating a novel non-invasive breath test for the detection of early-stage liver cirrhosis. The gold standard for confirming the diagnosis is a liver biopsy. The researchers conduct a study involving $800$ adult patients with chronic liver disease.

The results of the study are as follows:
- Liver biopsy confirms early-stage cirrhosis in $200$ patients.
- Among these $200$ patients, $180$ have a positive breath test.
- Among the $600$ patients without cirrhosis on biopsy, $60$ have a positive breath test.

What is the positive predictive value of the novel breath test in this study cohort? Provide your answer as a whole number percentage.

A public health department conducts a 10-year prospective cohort study to evaluate the association between a diet high in ultra-processed foods and the development of metabolic syndrome. The study enrolls 10,000 healthy adults without pre-existing metabolic conditions. Participants are categorized into two groups based on detailed dietary questionnaires. Over the 10-year follow-up period, the occurrence of new metabolic syndrome diagnoses is recorded. The results are summarized in the table below:

Based on these study results, what percentage of metabolic syndrome cases among the participants with high consumption of ultra-processed foods can be attributed to their dietary pattern?

Researchers conduct a randomized controlled trial to evaluate the efficacy of a novel recombinant vaccine against respiratory syncytial virus (RSV) in older adults. A total of 16,000 healthy volunteers aged 65 years and older are enrolled and randomly assigned in a 1:1 ratio to receive either the vaccine or a placebo. Over a 24-month follow-up period, the investigators record the incidence of severe lower respiratory tract disease (LRTD) confirmed by laboratory testing. The results are summarized in the following table:

Based on these study results, what is the number needed to treat (NNT) to prevent one case of severe LRTD?

An industrial city's health department is planning an intervention to completely eliminate occupational exposure to a specific aerosolized solvent. Historical data show that 30% of the city's adult residents are exposed to this solvent at their workplaces. Extensive cohort studies have demonstrated that the relative risk of developing a severe demyelinating neuropathy in exposed residents compared to unexposed residents is $3.0$. The baseline annual incidence of this neuropathy in the unexposed population is $5$ cases per $1,000$ people.

Assuming the intervention successfully reduces exposure to zero with an immediate effect on risk, and the population size remains stable, how many incident cases of this neuropathy will be prevented per $100,000$ residents in the first year?

Occupational health physicians are investigating the respiratory effects of prolonged exposure to a novel industrial solvent used in paint manufacturing. A longitudinal study follows employees at several facilities over a 10-year period. The study includes $1,500$ floor workers who directly handle the solvent and $4,500$ administrative staff at the same facilities who have no direct solvent exposure. Over the study duration, $120$ of the floor workers and $90$ of the administrative staff are newly diagnosed with adult-onset asthma. Based on these results, what percentage of the asthma cases among the floor workers is theoretically attributable to their solvent exposure?

Public health researchers are analyzing data from a recent prospective cohort study investigating the adverse effects of a new oral synthetic retinoid used for severe nodular acne. The study followed $400$ patients taking the new retinoid and $400$ patients taking standard topical therapies for one year. During the study period, $50$ patients in the new retinoid group developed significantly elevated liver transaminases. In the standard therapy group, $10$ patients developed similar transaminase elevations. Based on these findings, what is the number needed to harm (NNH) for the new oral synthetic retinoid compared to standard therapy?

Investigators are designing a clinical trial to evaluate a novel monoclonal antibody for the treatment of severe asthma. During the study design phase, they establish an acceptable probability of a Type I error ($\alpha$) at $0.05$. They also calculate that the probability of failing to reject the null hypothesis when it is actually false is $0.20$. What is the statistical power of this study expressed as a percentage?

A prospective cohort study is conducted to evaluate the association between a severe sedentary lifestyle and the development of peripheral artery disease (PAD). The study enrolls 10,000 middle-aged adults without preexisting cardiovascular disease. At baseline, researchers identify that 2,500 participants meet the criteria for a severe sedentary lifestyle. Over a 10-year follow-up period, 250 of the participants with a severe sedentary lifestyle develop PAD. During the same period, 150 of the remaining participants develop PAD.

Based on these findings, what percentage of the overall PAD incidence in this study population is directly attributable to a severe sedentary lifestyle? (Provide your answer as a numerical percentage).

Emergency medicine researchers are investigating a novel rapid point-of-care ultrasound algorithm for deep vein thrombosis (DVT). In their study cohort of symptomatic patients with a high pre-test probability, the true prevalence of DVT is $40\%$.

During the initial evaluation using standard diagnostic criteria, the algorithm yields a sensitivity of $85\%$ and a specificity of $85\%$.

To minimize missed diagnoses, the researchers broaden the criteria for a positive scan. Statistical analysis of the cohort reveals that this protocol change reduces the absolute number of false-negative results by exactly $50\%$ compared to the standard criteria. However, this adjustment simultaneously causes the absolute number of false-positive results to increase by exactly $100\%$ compared to the standard criteria.

Calculate the negative predictive value (NPV) of the ultrasound algorithm using the broadened criteria. Express your answer as a percentage rounded to the nearest whole number.

Researchers are designing a randomized, double-blind, placebo-controlled trial to evaluate the efficacy of a novel anti-obesity medication. Initially, the trial is designed to detect a mean weight loss difference of $5.0\text{ kg}$ between the treatment and placebo groups. Based on pilot data, the expected standard deviation of weight loss is estimated at $10.0\text{ kg}$ in both groups. Using a two-sided $\alpha$ of $0.05$ and $80\%$ power, the investigators calculate a required sample size of $64$ participants per group.

Prior to patient enrollment, a newly published meta-analysis indicates a larger population variability, suggesting the true standard deviation is $15.0\text{ kg}$. In light of this, the investigators revise their protocol to ensure even more conservative clinical benefits can be detected, setting the new minimum detectable mean difference at $3.0\text{ kg}$.

Assuming the type I error rate ($\alpha$) and statistical power remain unchanged, what is the newly calculated required sample size per group?

A prospective cohort study is conducted to evaluate the association between a diet high in ultra-processed foods and the development of colorectal cancer. The investigators enroll 50,000 healthy adults aged 45 to 60 years. At baseline, participants complete detailed dietary questionnaires and are categorized based on their dietary patterns. The high ultra-processed food (UPF) consumption group includes 10,000 participants, while the low UPF consumption group includes 40,000 participants.

All participants are followed for 15 years. During the follow-up period, 400 incident cases of colorectal cancer are diagnosed among the participants in the high UPF group. In the low UPF group, 400 incident cases of colorectal cancer are diagnosed.

Based on the study results, what percentage of the colorectal cancer cases among the participants with high ultra-processed food consumption is attributable to their high UPF diet?