A retrospective study was conducted in a US county in order to determine the frequency of hypodontia (tooth agenesis), the most common craniofacial malformation in humans, as well as to assess the need for an interdisciplinary approach to managing subsequent functional and esthetic sequelae in a target population. Using a dental administration computer software tool, a total of 1498 patients who visited the outpatient clinic of a large specialist dental center between April 2017 and February 2018 were identified. The group comprised 766 women and 732 men. Hypodontia was found in 6.3% of the patients, a rate that was consistent with the average values found in the published medical literature. Which measure of frequency was used to describe the percentage of patients affected by hypodontia in this example?
Q82
Researchers are studying the effects of a new medication for the treatment of type 2 diabetes. A randomized group of 100 subjects is given the new medication 1st for 2 months, followed by a washout period of 2 weeks, and then administration of the gold standard medication for 2 months. Another randomized group of 100 subjects is given the gold standard medication 1st for 2 months, followed by a washout period of 2 weeks, and then administration of the new medication for 2 months. What is the main disadvantage of this study design?
Q83
You are interested in studying the etiology of heart failure reduced ejection fraction (HFrEF) and attempt to construct an appropriate design study. Specifically, you wish to look for potential causality between dietary glucose consumption and HFrEF. Which of the following study designs would allow you to assess for and determine this causality?
Q84
A group of researchers aimed to study the association between phosphate levels in plasma and renal function decline in pre-dialysis patients. The study started in 2018 by including incident pre-dialysis patients (with chronic kidney disease in stage IV or V) who were already included in pre-dialysis care procedures between 2014 and 2016. These patients were subsequently found in the records of the hospitals participating in the study, and patient files were used to note the laboratory measurements at baseline. The medical courses of those patients were then followed through the medical charts (most notably their decline in renal function) until the start of dialysis, their death, or January 1, 2018. From this data, the researchers calculated that faster declines in renal function were linked to higher phosphate levels at baseline. Moreover, a relative risk for dying (1.5-fold) could be calculated for every mg/dL increase in phosphate levels. Hence, a high plasma phosphate level was shown to be an independent risk factor for not only a more rapid decline in renal function but also for higher mortality rates during the pre-dialysis phase. What is the main limitation of this type of observational study approach?
Q85
In a recently conducted case-control study that aimed to elucidate the causes of myelomeningocele (a neural tube defect in which there is an incomplete formation of the spinal bones), 200 mothers of infants born with the disease and 200 mothers of infants born without the disease were included in the study. Among the mothers of infants with myelomeningocele, 50% reported having experienced pharyngitis (sore throat) during pregnancy, compared with 5% of the mothers whose infants did not develop the condition. The researchers concluded that there is an association between pharyngitis during pregnancy and myelomeningocele; this conclusion was backed up by statistical analysis of the obtained results. Which type of bias may hamper the validity of the researchers’ conclusions?
Q86
A cross-sectional study of 650 patients with confirmed bronchogenic carcinoma was conducted in patients of all age groups in order to establish a baseline picture for further mortality comparisons. All patients were investigated using thoracic ultrasound and computed tomography of the chest. Also, data about the size of the mass, invasion of lymph nodes and chest wall, pleural effusion, and eventual paralysis of the diaphragm were noted. The bias that can arise in this case, and that may hamper further conclusions on the aggressiveness and mortality of bronchogenic carcinoma, may be explained as a tendency to which of the following aspects?
Q87
The mean, median, and mode weight of 37 newborns in a hospital nursery is 7 lbs 2 oz. In fact, there are 7 infants in the nursery that weigh exactly 7 lbs 2 oz. The standard deviation of the weights is 2 oz. The weights follow a normal distribution. A newborn delivered at 10 lbs 2 oz is added to the data set. What is most likely to happen to the mean, median, and mode with the addition of this new data point?
Q88
A first-year medical student is conducting a summer project with his medical school's pediatrics department using adolescent IQ data from a database of 1,252 patients. He observes that the mean IQ of the dataset is 100. The standard deviation was calculated to be 10. Assuming that the values are normally distributed, approximately 87% of the measurements will fall in between which of the following limits?
Q89
In order to study the association between coffee drinking and the subsequent development of lung cancer, a group of researchers decides to carry out a multicentric case-control study with a large number of participants—800 with a diagnosis of lung cancer, and 800 as age-adjusted controls. According to the results outlined in the table below, 80% of those with lung cancer were regular coffee drinkers, resulting in an odds ratio of 23.
Table: Contingency table of coffee drinking in relation to the presence of lung cancer
Lung cancer present Lung cancer absent
Coffee drinking 640 120
No coffee drinking 160 680
The researchers concluded from this that regular consumption of coffee is strongly linked to the development of lung cancer. Which of the following systematic errors did they not take into account?
Q90
A 42-year-old man presents to his primary care provider for a follow-up appointment after a new diagnosis of hypertension. The doctor mentions that a recent study examined the effect of a healthy lifestyle education program on blood pressure in 2 matched rural communities. One community received the health education program and the other did not. What is the type of study most likely being described here?
Study Design US Medical PG Practice Questions and MCQs
Question 81: A retrospective study was conducted in a US county in order to determine the frequency of hypodontia (tooth agenesis), the most common craniofacial malformation in humans, as well as to assess the need for an interdisciplinary approach to managing subsequent functional and esthetic sequelae in a target population. Using a dental administration computer software tool, a total of 1498 patients who visited the outpatient clinic of a large specialist dental center between April 2017 and February 2018 were identified. The group comprised 766 women and 732 men. Hypodontia was found in 6.3% of the patients, a rate that was consistent with the average values found in the published medical literature. Which measure of frequency was used to describe the percentage of patients affected by hypodontia in this example?
A. Attack rate
B. Cumulative incidence
C. Point prevalence
D. Period prevalence (Correct Answer)
E. Incidence rate
Explanation: ***Period prevalence***
- **Period prevalence** measures the proportion of individuals in a population who have a disease at any point during a specified time period, which in this study is from April 2017 to February 2018.
- The study identified patients with hypodontia within this timeframe, representing existing and new cases during that **period**.
*Attack rate*
- **Attack rate** is a specific type of incidence rate used typically during outbreaks, representing the proportion of exposed individuals who become ill during a defined short period.
- This scenario describes a retrospective study over a longer period, not an acute outbreak.
*Cumulative incidence*
- **Cumulative incidence** is the proportion of a population at risk that develops the disease over a specified follow-up period.
- While it describes new cases over a period, it specifically requires a **disease-free population at baseline** and follow-up for new occurrences, which is not stated for all 1498 patients.
*Point prevalence*
- **Point prevalence** measures the proportion of individuals having a disease at a single, specific point in time.
- The study describes patients identified over a range of months (April 2017 to February 2018), not a single point in time.
*Incidence rate*
- The **incidence rate** (or incidence density) measures how quickly new cases of a disease develop in a population over a specified time, taking into account the person-time at risk.
- The study primarily focuses on the **proportion of existing cases** observed over a period, rather than the rate of new case development while accounting for person-time.
Question 82: Researchers are studying the effects of a new medication for the treatment of type 2 diabetes. A randomized group of 100 subjects is given the new medication 1st for 2 months, followed by a washout period of 2 weeks, and then administration of the gold standard medication for 2 months. Another randomized group of 100 subjects is given the gold standard medication 1st for 2 months, followed by a washout period of 2 weeks, and then administration of the new medication for 2 months. What is the main disadvantage of this study design?
A. Hawthorne effect
B. Increasing selection bias
C. Increasing confounding bias
D. Decreasing power
E. Carryover effect (Correct Answer)
Explanation: ***Carryover effect***
- The primary disadvantage here is the **carryover effect**, where the effects of the first treatment (new medication or gold standard) may persist into the period when the second treatment is administered, even after a washout period.
- This can **mask or alter the true effect** of the second treatment, making it difficult to accurately assess their individual efficacy.
*Hawthorne effect*
- The **Hawthorne effect** refers to subjects improving their behavior or performance in response to being observed or studied, not specifically an issue with sequential treatment administration.
- It would affect both groups equally and doesn't explain a disadvantage inherent to the crossover design itself.
*Increasing selection bias*
- **Selection bias** occurs when the randomization process fails to create comparable groups, but this study design involves **randomization** into two groups, and then a crossover, which typically aims to *reduce* selection bias by having each participant serve as their own control.
- The sequential administration within a randomized crossover design actually helps to mitigate selection bias between treatment arms.
*Increasing confounding bias*
- **Confounding bias** occurs when an unmeasured variable is associated with both the exposure and the outcome, distorting the observed relationship.
- This crossover design, where each participant receives both treatments, is intended to *reduce* confounding by inter-individual variability, as each subject acts as their own control, rather than increasing it.
*Decreasing power*
- **Power** is the ability of a study to detect a true effect if one exists. Crossover designs often *increase* statistical power compared to parallel designs because each participant receives both treatments, reducing inter-individual variability.
- This design typically requires a smaller sample size to achieve the same power as a parallel group study, so decreased power is not a disadvantage.
Question 83: You are interested in studying the etiology of heart failure reduced ejection fraction (HFrEF) and attempt to construct an appropriate design study. Specifically, you wish to look for potential causality between dietary glucose consumption and HFrEF. Which of the following study designs would allow you to assess for and determine this causality?
A. Cross-sectional study
B. Case series
C. Cohort study (Correct Answer)
D. Case-control study
E. Randomized controlled trial
Explanation: ***Cohort study***
- A **cohort study** observes a group of individuals over time to identify risk factors and outcomes, allowing for the assessment of **temporal relationships** between exposure (dietary glucose) and outcome (HFrEF).
- This design is suitable for establishing a potential **causal link** as it tracks participants from exposure to outcome, enabling the calculation of incidence rates and relative risks.
*Cross-sectional study*
- A **cross-sectional study** measures exposure and outcome simultaneously at a single point in time, making it impossible to determine the **temporal sequence** of events.
- This design can only identify **associations** or correlations, not causation, as it cannot establish whether high glucose consumption preceded HFrEF.
*Case series*
- A **case series** describes characteristics of a group of patients with a particular disease or exposure, often to highlight unusual clinical features, but it lacks a **comparison group**.
- It cannot assess causality because it does not provide information on the frequency of exposure in healthy individuals or the incidence of the disease in unexposed individuals.
*Case-control study*
- A **case-control study** compares individuals with the outcome (cases) to those without the outcome (controls) to determine past exposures, which makes it prone to **recall bias**.
- While it can suggest associations, it cannot definitively establish a temporal relationship or causation as the outcome is already known when exposure is assessed.
*Randomized controlled trial*
- A **randomized controlled trial (RCT)** is the gold standard for establishing causation by randomly assigning participants to an intervention or control group, but it may not be ethical or feasible for studying long-term dietary exposures and chronic diseases like HFrEF due to the long follow-up period and complexity of diet.
- While ideal for causality, directly controlling and randomizing dietary glucose intake over decades to observe HFrEF development might be practically challenging or unethical.
Question 84: A group of researchers aimed to study the association between phosphate levels in plasma and renal function decline in pre-dialysis patients. The study started in 2018 by including incident pre-dialysis patients (with chronic kidney disease in stage IV or V) who were already included in pre-dialysis care procedures between 2014 and 2016. These patients were subsequently found in the records of the hospitals participating in the study, and patient files were used to note the laboratory measurements at baseline. The medical courses of those patients were then followed through the medical charts (most notably their decline in renal function) until the start of dialysis, their death, or January 1, 2018. From this data, the researchers calculated that faster declines in renal function were linked to higher phosphate levels at baseline. Moreover, a relative risk for dying (1.5-fold) could be calculated for every mg/dL increase in phosphate levels. Hence, a high plasma phosphate level was shown to be an independent risk factor for not only a more rapid decline in renal function but also for higher mortality rates during the pre-dialysis phase. What is the main limitation of this type of observational study approach?
A. Lack of inter-rater reliability
B. Selection based on the exposure status
C. Hypotheses generation
D. Significant time commitment
E. Inability to control for specific factors (Correct Answer)
Explanation: ***Inability to control for specific factors***
- Observational studies, especially **retrospective** ones like this, are inherently limited in their ability to control for all **confounding variables** that might influence both phosphate levels and renal function decline or mortality.
- The study notes that higher phosphate was an "independent risk factor," but without active intervention and randomization, unmeasured or uncontrolled confounders could still be at play, affecting the observed association.
*Lack of inter-rater reliability*
- This limitation primarily applies to studies where subjective assessments are made by multiple observers, such as interpreting imaging results or grading symptoms.
- The study primarily relies on **objective laboratory measurements** (phosphate levels, renal function) and medical chart data, where inter-rater reliability is less of a concern than in diagnostic assessments.
*Selection based on the exposure status*
- This describes a **case-control study design**, where participants are selected based on whether they have the outcome (e.g., disease) or not.
- The described study design is closer to a **retrospective cohort study**, where patients are identified from a past point (2014-2016) and followed forward in time (until 2018) to observe outcomes, rather than being selected by exposure status at the outset of the research question.
*Hypotheses generation*
- This is typically a strength, not a limitation, of observational studies, as they can identify potential associations that can then be tested in more rigorous experimental designs.
- The study successfully generated the hypothesis that high plasma phosphate is a risk factor for renal decline and mortality, indicating a useful outcome rather than a drawback.
*Significant time commitment*
- While research often requires significant time, this is a practical constraint rather than a methodological limitation inherent to the study's ability to establish valid associations.
- Moreover, this study design is **retrospective**, using existing data, which often *reduces* the time commitment compared to prospective studies that track patients forward from a new enrollment.
Question 85: In a recently conducted case-control study that aimed to elucidate the causes of myelomeningocele (a neural tube defect in which there is an incomplete formation of the spinal bones), 200 mothers of infants born with the disease and 200 mothers of infants born without the disease were included in the study. Among the mothers of infants with myelomeningocele, 50% reported having experienced pharyngitis (sore throat) during pregnancy, compared with 5% of the mothers whose infants did not develop the condition. The researchers concluded that there is an association between pharyngitis during pregnancy and myelomeningocele; this conclusion was backed up by statistical analysis of the obtained results. Which type of bias may hamper the validity of the researchers’ conclusions?
A. Recall bias (Correct Answer)
B. Assessment bias
C. Neyman bias
D. Surveillance bias
E. Attrition bias
Explanation: ***Recall bias***
- **Recall bias** occurs when participants in a study remember past events or exposures differently based on their current health status or outcome. In this case, mothers of infants with myelomeningocele (cases) may be more likely to **over-report or more accurately recall** past exposures like pharyngitis during pregnancy, due to their search for a potential cause for their child's condition, compared to mothers of healthy infants (controls).
- This differential recall can lead to a **misclassification of exposure** and an artificially inflated association between pharyngitis and myelomeningocele, thus hampering the validity of the study's conclusions.
*Assessment bias*
- **Assessment bias**, or observer bias, occurs when the **investigator's knowledge** of a participant's exposure or disease status influences the assessment of outcome or exposure.
- This scenario describes a difference in participant *recall*, not an interviewer's or researcher's systematic error in measuring or interpreting data.
*Neyman bias*
- **Neyman bias**, or prevalence-incidence bias, is a form of selection bias where the **prevalence of a disease** is used to approximate its incidence, leading to biased results because individuals with rapidly fatal or quickly resolved diseases are underrepresented.
- This bias is not relevant to the described situation, as the study is a case-control design looking at past exposures, not disease duration or survival.
*Surveillance bias*
- **Surveillance bias** occurs when one group is **monitored more intensely** for an outcome than another, leading to an artificially higher detection rate in the more scrutinized group.
- In this study, both groups of mothers are being asked about a past exposure (pharyngitis), not being differentially monitored for a new outcome, thus surveillance bias is less likely.
*Attrition bias*
- **Attrition bias** (or loss to follow-up bias) occurs in prospective studies (like cohort studies) when there are **differential rates of withdrawal** or loss of participants from study groups.
- This is a case-control study, which retrospective in nature, where participants are selected based on their outcome status (myelomeningocele or not) and then asked about past exposures; thus, attrition bias is not applicable.
Question 86: A cross-sectional study of 650 patients with confirmed bronchogenic carcinoma was conducted in patients of all age groups in order to establish a baseline picture for further mortality comparisons. All patients were investigated using thoracic ultrasound and computed tomography of the chest. Also, data about the size of the mass, invasion of lymph nodes and chest wall, pleural effusion, and eventual paralysis of the diaphragm were noted. The bias that can arise in this case, and that may hamper further conclusions on the aggressiveness and mortality of bronchogenic carcinoma, may be explained as a tendency to which of the following aspects?
A. Uncover more indolent cases of the disease preferentially (Correct Answer)
B. Detect only asymptomatic cases of the disease
C. Find more cases of the disease in older cohorts
D. Observe only the late stages of a disease with more severe manifestations
E. Identify more instances of fatal disease
Explanation: ***Uncover more indolent cases of the disease preferentially***
- This scenario describes **length-time bias**, which occurs in studies that identify prevalent cases, especially through screening. This method tends to disproportionately capture **slow-growing, less aggressive cases** of a disease because they survive longer and are more likely to be present at the time of the study.
- The study's focus on confirmed cases across all age groups to establish a baseline for mortality comparisons means that individuals with rapidly fatal forms of bronchogenic carcinoma might have already succumbed to the disease and thus are less likely to be included in the prevalent cohort.
*Detect only asymptomatic cases of the disease*
- The study investigated patients with "confirmed bronchogenic carcinoma," implying that the cases were already diagnosed, potentially due to symptoms or incidental findings. This bias description is more reflective of **ascertainment bias** during initial detection, not necessarily the inherent bias of a prevalent cohort study for mortality comparison.
- While some cases might have been asymptomatic, the study design doesn't exclusively target or only detect such cases; it includes all confirmed cases, regardless of symptom status at diagnosis.
*Find more cases of the disease in older cohorts*
- While age can be a risk factor for bronchogenic carcinoma, the bias described in the question primarily relates to the **duration of the disease** (i.e., fast vs. slow progression), not exclusively the age of the patients.
- The study included "patients of all age groups," so while older patients might have more prevalent disease, this option does not directly address the survival bias inherent in using prevalent cases for mortality comparison.
*Observe only the late stages of a disease with more severe manifestations*
- This option describes a bias that would typically lead to an overestimation of disease severity and mortality, which is the opposite of what is expected from **length-time bias**. Studies that only observe late stages might miss the full spectrum of the disease, including less severe cases.
- In a prevalent cohort study like this, the longer-surviving (and often less aggressive) cases are more likely to be captured, making it less likely to observe *only* the late stages with severe manifestations.
*Identify more instances of fatal disease*
- This is incorrect because **length-time bias** actually causes studies to underestimate the true fatality rate. By including disproportionately more prevalent (i.e., longer-surviving) cases, the observed disease course might appear less lethal than it truly is for those who succumb more rapidly.
- Patients with rapidly fatal forms of bronchogenic carcinoma would likely have died before being included in the prevalent cohort, thus leading to an underrepresentation of fatal cases.
Question 87: The mean, median, and mode weight of 37 newborns in a hospital nursery is 7 lbs 2 oz. In fact, there are 7 infants in the nursery that weigh exactly 7 lbs 2 oz. The standard deviation of the weights is 2 oz. The weights follow a normal distribution. A newborn delivered at 10 lbs 2 oz is added to the data set. What is most likely to happen to the mean, median, and mode with the addition of this new data point?
A. The mean will increase; the median will increase; the mode will stay the same
B. The mean will increase; the median will stay the same; the mode will stay the same (Correct Answer)
C. The mean will stay the same; the median will increase; the mode will stay the same
D. The mean will increase; the median will increase; the mode will increase
E. The mean will stay the same; the median will increase; the mode will increase
Explanation: ***The mean will increase; the median will stay the same; the mode will stay the same***
- The **mean** is highly sensitive to outliers. Adding a newborn weighing 10 lbs 2 oz (significantly heavier than the original mean of 7 lbs 2 oz) will increase the total sum of weights, thus **increasing the mean**.
- The **median** is the middle value in an ordered dataset. With 37 newborns, the median is the 19th value. Adding one more (38 total) makes the median the average of the 19th and 20th values. Since the new value (10 lbs 2 oz) is added at the extreme high end of the distribution, the 19th and 20th positions contain the same values as before. Therefore, the median will **stay the same**.
- The **mode** is the most frequent value. Since there are 7 infants already at 7 lbs 2 oz, adding a single infant at 10 lbs 2 oz will not change the most frequent weight in the dataset. The mode will **stay the same** at 7 lbs 2 oz.
*The mean will increase; the median will increase; the mode will stay the same*
- While the **mean will increase** due to the added outlier, the **median will not change**. With 38 observations, the median becomes the average of the 19th and 20th values, which remain unchanged since the outlier is added at position 38.
- The **mode** correctly stays at 7 lbs 2 oz as the new data point does not become the most frequent value.
*The mean will stay the same; the median will increase; the mode will stay the same*
- The **mean will not stay the same** because an outlier significantly higher than the current mean will always pull the mean higher.
- The **median will also not increase** as the middle values (19th and 20th positions) remain unchanged when adding an extreme outlier.
*The mean will increase; the median will increase; the mode will increase*
- While the **mean will increase**, the **median will not change** because the middle positions are unaffected by adding one extreme outlier.
- The **mode will not change** as the new data point (10 lbs 2 oz) is unique and doesn't become the most frequent value; 7 lbs 2 oz remains most frequent with 7 occurrences.
*The mean will stay the same; the median will increase; the mode will increase*
- This option is incorrect because the **mean will definitely increase** with the addition of a much larger value.
- The **median will not increase** as it depends on the middle positions, not extreme values.
- The **mode will not increase** as adding one 10 lb 2 oz infant won't make that weight the most frequent.
Question 88: A first-year medical student is conducting a summer project with his medical school's pediatrics department using adolescent IQ data from a database of 1,252 patients. He observes that the mean IQ of the dataset is 100. The standard deviation was calculated to be 10. Assuming that the values are normally distributed, approximately 87% of the measurements will fall in between which of the following limits?
A. 85–115 (Correct Answer)
B. 95–105
C. 65–135
D. 80–120
E. 70–130
Explanation: ***85–115***
- For a **normal distribution**, approximately 87% of data falls within **±1.5 standard deviations** from the mean.
- With a mean of 100 and a standard deviation of 10, the range is 100 ± (1.5 * 10) = 100 ± 15, which gives **85–115**.
*95–105*
- This range represents **±0.5 standard deviations** from the mean (100 ± 5), which covers only about 38% of the data.
- This is a much narrower range and does not encompass 87% of the observations as required.
*65–135*
- This range represents **±3.5 standard deviations** from the mean (100 ± 35), which would cover over 99.9% of the data.
- Thus, this interval is too wide for 87% of the measurements.
*80–120*
- This range represents **±2 standard deviations** from the mean (100 ± 20), which covers approximately 95% of the data.
- While a common interval, it is wider than necessary for 87% of the data.
*70–130*
- This range represents **±3 standard deviations** from the mean (100 ± 30), which covers approximately 99.7% of the data.
- This interval is significantly wider than required to capture 87% of the data.
Question 89: In order to study the association between coffee drinking and the subsequent development of lung cancer, a group of researchers decides to carry out a multicentric case-control study with a large number of participants—800 with a diagnosis of lung cancer, and 800 as age-adjusted controls. According to the results outlined in the table below, 80% of those with lung cancer were regular coffee drinkers, resulting in an odds ratio of 23.
Table: Contingency table of coffee drinking in relation to the presence of lung cancer
Lung cancer present Lung cancer absent
Coffee drinking 640 120
No coffee drinking 160 680
The researchers concluded from this that regular consumption of coffee is strongly linked to the development of lung cancer. Which of the following systematic errors did they not take into account?
A. Information bias
B. Selection bias
C. Observer bias
D. Confounding bias (Correct Answer)
E. Attrition bias
Explanation: ***Confounding bias***
- The calculated **odds ratio of 23** suggests a very strong association, which is highly unlikely for coffee as a direct cause of lung cancer and points to the presence of a **confounding variable**.
- A major **confounder** in studying coffee and lung cancer is **smoking**, as smokers are often also coffee drinkers, and smoking is a known strong cause of lung cancer. The study did not appear to account for this.
*Information bias*
- This bias relates to **inaccurate data collection or measurement** of exposure or outcome, such as recall bias or measurement error.
- The scenario describes a problem with interpreting the relationship between variables, not flaws in data collection itself.
*Selection bias*
- This occurs when the **study participants are not representative** of the target population, leading to an incorrect estimate of the association.
- The description mentions a "large number of participants" and "age-adjusted controls," which suggests efforts were made to reduce selection bias, although it cannot be completely ruled out.
*Observer bias*
- This type of **information bias** occurs when the observer's knowledge of the study's aim or the participant's status influences their recording of data.
- The problem described is about the interpretation of the association between coffee and lung cancer, not about how observations were made and recorded.
*Attrition bias*
- This occurs in **longitudinal studies** due to **differential loss to follow-up** between exposure groups, leading to a biased sample at the end of the study.
- This is a **case-control study**, which measures exposure retrospectively and doesn't involve follow-up, hence attrition bias is not relevant here.
Question 90: A 42-year-old man presents to his primary care provider for a follow-up appointment after a new diagnosis of hypertension. The doctor mentions that a recent study examined the effect of a healthy lifestyle education program on blood pressure in 2 matched rural communities. One community received the health education program and the other did not. What is the type of study most likely being described here?
A. Community trial (Correct Answer)
B. Cross-sectional study
C. Crossover study
D. Case-control study
E. Explanatory study
Explanation: ***Community trial***
- A **community trial** involves intervention at the community level, comparing outcomes between communities that receive an intervention and those that do not, as described with the health education program in matched rural communities.
- This design is suitable for studying interventions aimed at influencing health behaviors or outcomes across entire populations.
*Cross-sectional study*
- A **cross-sectional study** assesses exposure and outcome at a single point in time, providing a "snapshot" and not suitable for evaluating the effect of an intervention over time.
- It does not involve tracking communities or individuals over time to observe changes due to an intervention.
*Crossover study*
- A **crossover study** involves subjects receiving a sequence of different treatments, with a washout period between treatments, often used in clinical drug trials.
- This design is not applicable here as the intervention is at the community level and does not involve alternating treatments within the same subjects/communities.
*Case-control trial*
- A **case-control study** compares individuals with a disease (cases) to individuals without the disease (controls) and retrospectively looks for differences in exposure.
- It is an observational study used to identify risk factors, not to evaluate the impact of an intervention program.
*Explanatory study*
- An **explanatory study** aims to clarify the 'how' or 'why' behind phenomena, focusing on cause-and-effect relationships or mechanisms.
- While a community trial is a type of explanatory study, "explanatory study" is too broad and not the most precise classification for this specific experimental design.
