A research group from a small outpatient clinic is investigating the health benefits of a supplement containing polyphenol-rich extract from pomegranate, as several studies have suggested that pomegranate juice may have antiatherogenic, antihypertensive, and anti-inflammatory effects. Two researchers involved in the study decide to measure blood glucose concentration and lipid profile postprandially (i.e. after a meal), as well as systolic and diastolic blood pressure. Their study group consists of 16 women over 50 years of age who live in the neighborhood in a small town where the clinic is located. The women are given the supplement in the form of a pill, which they take during a high-fat meal or 15 minutes prior to eating. Their results indicate that the supplement can reduce the postprandial glycemic and lipid response, as well as lower blood pressure. Based on their conclusions, the researchers decided to put the product on the market and to conduct a nation-wide marketing campaign. Which of the following is a systematic error present in the researchers’ study that hampers the generalization of their conclusions to the entire population?
Q42
A clinical trial is conducted to determine the efficacy of ginkgo biloba in the treatment of Parkinson disease. A sample of patients with Parkinson disease is divided into two groups. Participants in the first group are treated with ginkgo biloba, and participants in the other group receive a placebo. A change in the Movement Disorder Society-Unified Parkinson Disease Rating Scale (MDS-UPDRS) score is used as the primary endpoint for the study. The investigators, participants, and data analysts were meant to be blinded throughout the trial. However, while the trial is being conducted, the patients' demographics and their allocated treatment groups are mistakenly disclosed to the investigators, but not to the participants or the data analysts, because of a technical flaw. The study concludes that there is a significant decrease in MDS-UPDRS scores in patients treated with ginkgo biloba. Which of the following is most likely to have affected the validity of this study?
Q43
A 77-year-old female comes to a medical school's free clinic for follow-up examination after a urinary tract infection (UTI) and is seen by a fourth year medical student. The clinic serves largely uninsured low-income patients in a New York City neighborhood with a large African American and Latino population. Two weeks ago, the patient was treated in the local emergency department where she presented with altered mental state and dysuria. The medical student had recently read about a study that described a strong relationship between cognitive impairment and UTI hospitalization risk (RR = 1.34, p < 0.001). The attending physician at the medical student's free clinic is also familiar with this study and tells the medical student that the study was conducted in a sample of upper middle class Caucasian patients in the Netherlands. The attending states that the results of the study should be interpreted with caution. Which of the following concerns is most likely underlying the attending physician's remarks?
Q44
A scientist is trying to determine the proportion of white-eyed fruit flies in the environment. The white-eyed allele was found to be dominant to the red-eyed allele. The frequency of the red-eyed allele is 0.1. What is the proportion of flies who have white-eyes if the population is in Hardy Weinberg Equilibrium?
Q45
A 52-year-old man presents to the office for a diabetes follow-up visit. He currently controls his diabetes through lifestyle modification only. He monitors his blood glucose at home with a glucometer every day. He gives the doctor a list of his most recent early morning fasting glucose readings from the past 8 days which are: 128 mg/dL, 130 mg/dL, 132 mg/dL, 125 mg/dL, 134 mg/dL, 127 mg/dL, 128 mg/dL, and 136 mg/dL. Which of the following values is the median of this data set?
Q46
An epidemiologist is interested in studying the clinical utility of a free computerized social skills training program for children with autism. A total of 125 participants with autism (mean age: 12 years) were recruited for the study and took part in weekly social skills training sessions for 3 months. Participants were recruited from support groups in a large Northeastern US city for parents with autistic children. Parents in the support group were very eager to volunteer for the study, and over 300 children were placed on a waiting list while the study was conducted. At baseline and at the end of the 3-month period, participants were observed during a videotaped social play exercise and scored on a social interaction rating scale by their parents. Social interaction rating scores following the 3-month intervention were more than twice as high as baseline scores (p < 0.001). During exit interviews, one parent commented, "I knew from the start that this program was going to be life-changing for my son!" This sentiment was echoed by a number of other parents. Which of the following is the most likely explanation for the study's result?
Q47
Two studies are reviewed for submission to an oncology journal. In Study A, a novel MRI technology is evaluated as a screening tool for ovarian cancer. The authors find that the mean survival time is 4 years in the control group and 10 years in the MRI-screened group. In Study B, cognitive behavioral therapy (CBT) and a novel antidepressant are used to treat patients with comorbid pancreatic cancer and major depression. Patients receiving the new drug are told that they are expected to have quick resolution of their depression, while those who do not receive the drug are not told anything about their prognosis. Which of the following describes the likely type of bias in Study A and Study B?
Q48
A 2-month study is conducted to assess the relationship between the consumption of natural licorice and the development of hypokalemia. A total of 100 otherwise healthy volunteers are enrolled. Half of the volunteers are asked to avoid licorice and the other half are asked to consume licorice daily, along with their regular diet. All volunteers are monitored for the duration of the study and their serum potassium concentration is measured each week. No statistically significant difference in mean serum potassium concentrations is found between the volunteers who consumed licorice regularly and those avoiding licorice. The serum potassium concentrations remained within the range of 3.5–5.0 mEq/L in all volunteers from both groups. Two patients were excluded from the study after their baseline serum potassium concentrations were found to be 3.1 mEq/L and 3.3 mEq/L. If these patients had been included in the analysis, which of the following values would most likely have been unaffected?
Q49
A study is performed to determine whether cognitive behavioral therapy (CBT) increases compliance to dietary regimens. In order to test this hypothesis, a random group of volunteers who want to lose weight are selected from the community and subsequently randomized to no intervention and CBT groups. They are asked to record what they ate every day in a food journal and these recordings are correlated with objective serum and urine biomarkers for food intake. Surprisingly, it was found that even the group with no intervention had much higher rates of compliance to dietary regimens than the general population. Multivariate analysis showed no significant demographic or medical differences between the two groups. Which of the following most likely explains this finding from the study?
Q50
A medical student is sampling serum triglyceride values for a study on the effect of gemfibrozil on lipid levels. He draws blood from 6 different patients who have been fasting for a period of 9 hours. Laboratory results show:
Patient 1 175 mg/dL
Patient 2 150 mg/dL
Patient 3 196 mg/dL
Patient 4 160 mg/dL
Patient 5 170 mg/dL
Patient 6 175 mg/dL
Which of the following is the median of these serum triglyceride values?
Study Design US Medical PG Practice Questions and MCQs
Question 41: A research group from a small outpatient clinic is investigating the health benefits of a supplement containing polyphenol-rich extract from pomegranate, as several studies have suggested that pomegranate juice may have antiatherogenic, antihypertensive, and anti-inflammatory effects. Two researchers involved in the study decide to measure blood glucose concentration and lipid profile postprandially (i.e. after a meal), as well as systolic and diastolic blood pressure. Their study group consists of 16 women over 50 years of age who live in the neighborhood in a small town where the clinic is located. The women are given the supplement in the form of a pill, which they take during a high-fat meal or 15 minutes prior to eating. Their results indicate that the supplement can reduce the postprandial glycemic and lipid response, as well as lower blood pressure. Based on their conclusions, the researchers decided to put the product on the market and to conduct a nation-wide marketing campaign. Which of the following is a systematic error present in the researchers’ study that hampers the generalization of their conclusions to the entire population?
A. Late-look bias
B. Confounding bias
C. Design bias (Correct Answer)
D. Expectancy bias
E. Proficiency bias
Explanation: ***Correct: Design bias***
- The **study design** itself is a significant source of systematic error that hampers generalization to the entire population.
- The study lacks a **control group** for comparison, making it impossible to determine if the observed effects are truly due to the supplement or other factors.
- The sample is very **small (n=16)** and **unrepresentative** - only women over 50 from one neighborhood cannot represent the entire population.
- There is no **randomization** or **blinding**, and the sample is a convenience sample rather than a random sample.
- These fundamental design flaws prevent valid generalization of the findings to broader populations.
*Incorrect: Late-look bias*
- **Late-look bias** occurs when outcomes are assessed too late in the course of disease, potentially missing early effects or being influenced by late-occurring events.
- This bias is not evident here, as the study focuses on **immediate postprandial responses** and acute blood pressure changes, not long-term follow-up outcomes.
*Incorrect: Confounding bias*
- While potential confounders (e.g., diet, exercise, medications) may be present, **confounding bias** specifically refers to an unmeasured third variable that affects both the exposure and outcome.
- The most pressing issue hampering **generalization** is not confounding, but rather the **small, non-representative sample** and lack of control group - these are structural design limitations.
*Incorrect: Expectancy bias*
- **Expectancy bias** (also called observer-expectancy effect) occurs when researchers' or participants' expectations influence the results, such as through placebo effects or subjective interpretation of outcomes.
- While this could potentially occur due to lack of blinding, the most fundamental flaw hampering **generalization to the entire population** is the unrepresentative sample and poor study design structure.
*Incorrect: Proficiency bias*
- **Proficiency bias** relates to differences in the skills, experience, or techniques of those performing interventions or measurements, leading to variability in outcomes.
- There is no information suggesting that inconsistencies in measurement techniques or researcher proficiency are the primary source of systematic error in this study.
Question 42: A clinical trial is conducted to determine the efficacy of ginkgo biloba in the treatment of Parkinson disease. A sample of patients with Parkinson disease is divided into two groups. Participants in the first group are treated with ginkgo biloba, and participants in the other group receive a placebo. A change in the Movement Disorder Society-Unified Parkinson Disease Rating Scale (MDS-UPDRS) score is used as the primary endpoint for the study. The investigators, participants, and data analysts were meant to be blinded throughout the trial. However, while the trial is being conducted, the patients' demographics and their allocated treatment groups are mistakenly disclosed to the investigators, but not to the participants or the data analysts, because of a technical flaw. The study concludes that there is a significant decrease in MDS-UPDRS scores in patients treated with ginkgo biloba. Which of the following is most likely to have affected the validity of this study?
A. Effect modification
B. Recall bias
C. Pygmalion effect (Correct Answer)
D. Hawthorne effect
E. Procedure bias
Explanation: ***Pygmalion effect***
- The **Pygmalion effect**, also known as **observer-expectancy bias** or experimenter bias, occurs when an investigator's expectations about the outcome of a study unintentionally influence the results.
- In this case, the **investigators becoming unblinded** to treatment assignments could lead them to unconsciously influence patient assessments or interactions based on their knowledge of who received ginkgo biloba, potentially leading to inflated positive outcomes for the treatment group.
*Effect modification*
- **Effect modification** describes a phenomenon where the effect of an exposure on an outcome is different across various strata of a third variable.
- This is a true biological interaction and does not represent a bias or flaw in the study design due to unblinding.
*Recall bias*
- **Recall bias** occurs when participants' memories of past exposures or events differ based on their current health status or knowledge of their condition.
- This bias primarily affects studies that rely on **retrospective reporting** of past events and is not relevant to the unblinding of investigators in a prospective clinical trial.
*Hawthorne effect*
- The **Hawthorne effect** describes a phenomenon where participants in a study change their behavior simply because they are aware of being observed, regardless of the intervention they receive.
- While participant blinding is important to prevent this, the scenario describes investigators being unblinded, not the participants.
*Procedure bias*
- **Procedure bias** (also known as interviewer bias or performance bias) arises from systematic differences in the way data is collected or procedures are performed for different study groups.
- While investigator unblinding can lead to elements of procedure bias, the more specific and encompassing term for an investigator's expectations influencing results is the **Pygmalion effect** (observer-expectancy bias).
Question 43: A 77-year-old female comes to a medical school's free clinic for follow-up examination after a urinary tract infection (UTI) and is seen by a fourth year medical student. The clinic serves largely uninsured low-income patients in a New York City neighborhood with a large African American and Latino population. Two weeks ago, the patient was treated in the local emergency department where she presented with altered mental state and dysuria. The medical student had recently read about a study that described a strong relationship between cognitive impairment and UTI hospitalization risk (RR = 1.34, p < 0.001). The attending physician at the medical student's free clinic is also familiar with this study and tells the medical student that the study was conducted in a sample of upper middle class Caucasian patients in the Netherlands. The attending states that the results of the study should be interpreted with caution. Which of the following concerns is most likely underlying the attending physician's remarks?
A. Confounding bias
B. Selection bias
C. Poor reliability
D. Low internal validity
E. Low external validity (Correct Answer)
Explanation: ***Low external validity***
- **External validity** refers to the generalizability of study findings to other populations, settings, or times.
- The findings from a study of **upper-middle-class Caucasian patients in the Netherlands** may not apply to low-income African American and Latino patients in New York City due to socioeconomic, genetic, and environmental differences, leading to low external validity.
*Confounding bias*
- **Confounding bias** occurs when an unobserved variable is associated with both the exposure and the outcome, distorting their true relationship.
- While confounding can affect internal validity, the attending's concern is specifically about the applicability of the findings to a different population, not the initial study's internal integrity.
*Selection bias*
- **Selection bias** arises when the study participants are not representative of the target population, often leading to systematic differences between groups.
- While the *initial study* might have had its own selection bias if its sample wasn't representative of the Netherlands population, the attending's concern relates to applying its findings to a *different* population.
*Poor reliability*
- **Reliability** refers to the consistency or reproducibility of a measurement or study result over time or across different observers.
- This concern is about the generalizability of the findings to a different population, not whether the initial study's measurements or results were inconsistent.
*Low internal validity*
- **Internal validity** refers to the extent to which a study establishes a cause-and-effect relationship between the intervention/exposure and the outcome within its own sample.
- The attending's concern is not that the study itself was poorly conducted or failed to demonstrate a true association within its *own* population, but rather that its findings may not hold true for *other* populations.
Question 44: A scientist is trying to determine the proportion of white-eyed fruit flies in the environment. The white-eyed allele was found to be dominant to the red-eyed allele. The frequency of the red-eyed allele is 0.1. What is the proportion of flies who have white-eyes if the population is in Hardy Weinberg Equilibrium?
A. 1%
B. 81%
C. 18%
D. 10%
E. 99% (Correct Answer)
Explanation: ***99%***
- In **Hardy-Weinberg equilibrium**, the frequencies of alleles and genotypes remain constant from generation to generation. The frequency of the dominant allele (W) is represented by 'p', and the frequency of the recessive allele (w) is represented by 'q'.
- Given that the **red-eyed allele is recessive** (w) and has a frequency of **q = 0.1**, then the frequency of the **white-eyed allele (W)**, which is dominant, is **p = 1 - q = 1 - 0.1 = 0.9**.
- The proportion of the population with white eyes includes homozygous dominant individuals (WW) and heterozygous individuals (Ww).
- The genotype frequencies are: WW = p² = (0.9)² = 0.81, and Ww = 2pq = 2(0.9)(0.1) = 0.18.
- Therefore, the proportion of white-eyed flies is **p² + 2pq = 0.81 + 0.18 = 0.99**, or **99%**.
*1%*
- This represents the frequency of the **homozygous recessive genotype (ww)**, which would be (0.1)² = 0.01 or 1%.
- Flies with the **ww genotype** would have **red eyes**, not white eyes.
*81%*
- This represents the frequency of the **homozygous dominant genotype (WW)**, which is p² = (0.9)² = 0.81 or 81%.
- However, white-eyed flies also include **heterozygous individuals (Ww)**, so 81% is an underestimation of the total proportion of white-eyed flies.
*18%*
- This represents the frequency of the **heterozygous genotype (Ww)**, which is 2pq = 2(0.9)(0.1) = 0.18 or 18%.
- This includes only part of the white-eyed population and does not account for the **homozygous dominant (WW) individuals**.
*10%*
- This represents the frequency of the **recessive allele (q)**, which is 0.1 or 10%.
- This is an allele frequency, not a **genotype or phenotype frequency** in the population.
Question 45: A 52-year-old man presents to the office for a diabetes follow-up visit. He currently controls his diabetes through lifestyle modification only. He monitors his blood glucose at home with a glucometer every day. He gives the doctor a list of his most recent early morning fasting glucose readings from the past 8 days which are: 128 mg/dL, 130 mg/dL, 132 mg/dL, 125 mg/dL, 134 mg/dL, 127 mg/dL, 128 mg/dL, and 136 mg/dL. Which of the following values is the median of this data set?
A. 132 mg/dL
B. 129 mg/dL (Correct Answer)
C. 128 mg/dL
D. 127 mg/dL
E. 130 mg/dL
Explanation: ***129 mg/dL***
- To find the **median** of an **even set of numbers**, arrange the set in ascending order: 125, 127, 128, 128, 130, 132, 134, 136. The two middle values are 128 and 130.
- The median is the **average of these two middle numbers**: (128 + 130) / 2 = 129 mg/dL.
*132 mg/dL*
- This is one of the higher values in the dataset and would be the **median** only if the dataset had a different distribution or an odd number of data points with 132 in the middle.
- The correct calculation for the given dataset requires averaging the two central values, not selecting a single value from the upper half.
*128 mg/dL*
- This value is one of the two **middle numbers** when the set is ordered, but it is not the median for an even set.
- The **median** for an even set of data involves finding the average of the two middle numbers, not just taking one of them.
*127 mg/dL*
- This value is in the lower half of the **ordered dataset** and is not one of the two central values.
- It would not be considered the median since the median is the value that **divides the data into two equal halves**.
*130 mg/dL*
- This is one of the two **middle numbers** when the data is ordered, similar to 128 mg/dL.
- While it's one of the data points used in the median calculation, it is not the **median itself** because the dataset contains an even number of points.
Question 46: An epidemiologist is interested in studying the clinical utility of a free computerized social skills training program for children with autism. A total of 125 participants with autism (mean age: 12 years) were recruited for the study and took part in weekly social skills training sessions for 3 months. Participants were recruited from support groups in a large Northeastern US city for parents with autistic children. Parents in the support group were very eager to volunteer for the study, and over 300 children were placed on a waiting list while the study was conducted. At baseline and at the end of the 3-month period, participants were observed during a videotaped social play exercise and scored on a social interaction rating scale by their parents. Social interaction rating scores following the 3-month intervention were more than twice as high as baseline scores (p < 0.001). During exit interviews, one parent commented, "I knew from the start that this program was going to be life-changing for my son!" This sentiment was echoed by a number of other parents. Which of the following is the most likely explanation for the study's result?
A. Sampling bias
B. Confounding bias
C. Recall bias
D. Social desirability bias
E. Observer bias (Correct Answer)
Explanation: ***Observer bias***
- Parents, acting as **observers**, rated their own children, leading to potential bias due to their **emotional involvement** and desire for a positive outcome.
- The parents' high expectations and positive sentiments, as indicated by the quote, suggest their ratings might have been influenced by their **hopes for the intervention**.
*Sampling bias*
- This refers to a non-randomized sampling of participants, which can affect the **generalizability** of results but not directly explain the observed increase in scores within the study group.
- While there might be some sampling bias (e.g., eager parents), it doesn't primarily explain the difference between pre- and post-intervention scores as reported.
*Confounding bias*
- Occurs when an **extraneous variable** is associated with both the exposure and the outcome, distorting the true relationship.
- While factors like parental involvement could be confounders, the direct increase in scores within the same individuals being observed by the same biased observers points more directly to observer bias.
*Recall bias*
- This bias arises when participants or observers remember past events differently based on their current state or knowledge, often seen in **retrospective studies**.
- In this study, the observers (parents) were completing ratings at baseline and after the intervention, so recall of past scores isn't the primary issue; rather, their subjective assessment of current behavior.
*Social desirability bias*
- This occurs when participants answer questions in a way that will be viewed favorably by others, often under-reporting undesirable behaviors or over-reporting desirable ones.
- While parents might want to appear as "good parents," the primary issue here is their observation and scoring of their child's social skills, which is more aligned with **observer bias** influencing their perceptions.
Question 47: Two studies are reviewed for submission to an oncology journal. In Study A, a novel MRI technology is evaluated as a screening tool for ovarian cancer. The authors find that the mean survival time is 4 years in the control group and 10 years in the MRI-screened group. In Study B, cognitive behavioral therapy (CBT) and a novel antidepressant are used to treat patients with comorbid pancreatic cancer and major depression. Patients receiving the new drug are told that they are expected to have quick resolution of their depression, while those who do not receive the drug are not told anything about their prognosis. Which of the following describes the likely type of bias in Study A and Study B?
A. Latency Bias; Golem effect
B. Confounding; Golem effect
C. Lead time bias; Golem effect
D. Lead time bias; Pygmalion effect (Correct Answer)
E. Latency bias; Pygmalion effect
Explanation: ***Lead time bias; Pygmalion effect***
- In Study A, the MRI technology detects ovarian cancer earlier, artificially making the survival time appear longer simply due to earlier diagnosis, not necessarily improved outcomes, which is characteristic of **lead time bias**.
- In Study B, the patients receiving the new drug are told to expect quick resolution of their depression, leading to increased expectation of improvement, which describes the **Pygmalion effect** (a form of observer-expectancy effect where higher expectations lead to increased performance).
*Latency Bias; Golem effect*
- **Latency bias** refers to a delay in the manifestation of an outcome, which is not the primary issue in Study A's screening context.
- The **Golem effect** is a form of negative self-fulfilling prophecy where lower expectations placed upon individuals by superiors/researchers lead to poorer performance, which is opposite to what is described in Study B.
*Confounding; Golem effect*
- **Confounding** occurs when an unmeasured third variable is associated with both the exposure and the outcome, distorting the observed relationship; while confounding is common, the scenario in Study A specifically points to a screening effect on survival time.
- As mentioned, the **Golem effect** refers to negative expectations leading to poorer outcomes, which is not present in Study B.
*Lead time bias; Golem effect*
- **Lead time bias** correctly identifies the issue in Study A, as explaining the apparently longer survival as a result of earlier detection.
- However, the **Golem effect** incorrectly describes the scenario in Study B, where positive expectations are given, not negative ones.
*Latency bias; Pygmalion effect*
- **Latency bias** is not the primary bias described in Study A; the immediate impact of early detection on survival statistics points to lead time bias.
- The **Pygmalion effect** correctly describes the bias in Study B, where positive expectations from the researchers influence patient outcomes.
Question 48: A 2-month study is conducted to assess the relationship between the consumption of natural licorice and the development of hypokalemia. A total of 100 otherwise healthy volunteers are enrolled. Half of the volunteers are asked to avoid licorice and the other half are asked to consume licorice daily, along with their regular diet. All volunteers are monitored for the duration of the study and their serum potassium concentration is measured each week. No statistically significant difference in mean serum potassium concentrations is found between the volunteers who consumed licorice regularly and those avoiding licorice. The serum potassium concentrations remained within the range of 3.5–5.0 mEq/L in all volunteers from both groups. Two patients were excluded from the study after their baseline serum potassium concentrations were found to be 3.1 mEq/L and 3.3 mEq/L. If these patients had been included in the analysis, which of the following values would most likely have been unaffected?
A. Variance
B. Mean
C. Median
D. Mode (Correct Answer)
E. Standard error
Explanation: ***Mode***
- The **mode** represents the most frequently occurring value in a dataset.
- In this dataset of 100 values distributed between 3.5-5.0 mEq/L, there is likely a value (or values) that appears most frequently.
- Adding only **2 additional values** (3.1 and 3.3 mEq/L) would not change which value appears most frequently in the dataset.
- The mode is **robust to outliers** when the sample size is large relative to the number of outliers added.
*Variance*
- **Variance** measures the spread of data points around the mean.
- Adding values that are lower than the existing data points (3.1 and 3.3 mEq/L are below the observed range of 3.5-5.0) would increase the overall spread, thus **increasing the variance**.
*Mean*
- The **mean** is the average of all values in a dataset.
- Adding lower values (3.1 and 3.3 mEq/L) to the dataset would **decrease the overall mean**, as these values are below the current range.
*Median*
- The **median** is the middle value in an ordered dataset.
- With 100 original values, the median would be between the 50th and 51st values when ordered.
- Adding 2 values at the lower end would shift the position, making the new median the average of the 51st and 52nd values in the expanded dataset, which could **change the median value**.
*Standard error*
- The **standard error** measures the precision of the sample mean and is calculated as: SE = Standard Deviation / √n.
- Adding these 2 values would change both the **standard deviation** (due to increased variance) and the **sample size** (from 100 to 102).
- Both changes would **affect the standard error**.
Question 49: A study is performed to determine whether cognitive behavioral therapy (CBT) increases compliance to dietary regimens. In order to test this hypothesis, a random group of volunteers who want to lose weight are selected from the community and subsequently randomized to no intervention and CBT groups. They are asked to record what they ate every day in a food journal and these recordings are correlated with objective serum and urine biomarkers for food intake. Surprisingly, it was found that even the group with no intervention had much higher rates of compliance to dietary regimens than the general population. Multivariate analysis showed no significant demographic or medical differences between the two groups. Which of the following most likely explains this finding from the study?
A. Confounding effect
B. Hawthorne effect (Correct Answer)
C. Recall bias
D. Pygmalion effect
E. Procedure bias
Explanation: ***Correct: Hawthorne effect***
- The **Hawthorne effect** describes the phenomenon where individuals modify their behavior in response to being observed or knowing they are part of a study. In this case, both groups knew they were being studied for dietary compliance, leading to increased adherence even in the control group.
- The act of **recording daily food intake** and the knowledge of participation in a study can itself serve as a motivator for improved compliance, leading to higher rates in both intervention and control groups compared to the general population.
*Incorrect: Confounding effect*
- A **confounding effect** occurs when an unmeasured or uncontrolled third variable influences both the independent and dependent variables, creating a spurious association. However, the study explicitly stated that "multivariate analysis showed no significant demographic or medical differences" between the groups, making confounding less likely.
- While confounding can occur in research, the specific scenario describing increased compliance due to awareness of observation is an example of the Hawthorne effect, not general confounding.
*Incorrect: Recall bias*
- **Recall bias** is a systematic error that occurs when there are differences in the accuracy or completeness of memories of past events between study participants. This typically happens in retrospective studies where participants are asked to remember past exposures or outcomes.
- While the study involved recording food intake, the problem describes an unexpected improvement in compliance across both groups due to participation, rather than a systematic distortion of reported past events. The recordings were real-time, reducing recall issues.
*Incorrect: Pygmalion effect*
- The **Pygmalion effect**, or Rosenthal effect, describes the phenomenon where higher expectations lead to an increase in performance. It usually refers to an effect on the participant's performance influenced by the experimenter's expectations.
- While expectations can influence behavior, the observation here is tied to the act of being studied and observed, rather than specific high expectations imposed by the researchers on the participants themselves.
*Incorrect: Procedure bias*
- **Procedure bias**, or selection bias, occurs when the procedures used to select participants or assign them to groups lead to systematic differences between the groups. This can affect the generalizability or internal validity of the study.
- The study explicitly states that participants were "randomly selected" and "randomized to no intervention and CBT groups," which aims to minimize procedure or selection bias. The observed effect applies to both groups, suggesting it's not due to a flaw in allocation.
Question 50: A medical student is sampling serum triglyceride values for a study on the effect of gemfibrozil on lipid levels. He draws blood from 6 different patients who have been fasting for a period of 9 hours. Laboratory results show:
Patient 1 175 mg/dL
Patient 2 150 mg/dL
Patient 3 196 mg/dL
Patient 4 160 mg/dL
Patient 5 170 mg/dL
Patient 6 175 mg/dL
Which of the following is the median of these serum triglyceride values?
A. 171.0 mg/dL
B. 160.0 mg/dL
C. 175.0 mg/dL
D. 170.0 mg/dL
E. 172.5 mg/dL (Correct Answer)
Explanation: ***172.5 mg/dL***
- To find the **median** for an even number of data points, arrange the values in ascending order: 150, 160, 170, 175, 175, 196. The two middle values are 170 and 175.
- The median is the **average of these two middle values**: (170 + 175) / 2 = 172.5 mg/dL.
*171.0 mg/dL*
- This value is incorrect because it represents a **calculated average** that is not derived from the correct middle numbers (170 and 175).
- It would be the result if one of the middle numbers was 167 or there was an error in calculating the average.
*160.0 mg/dL*
- This value is incorrect as it is the **second smallest value** in the dataset, not the middle value.
- It is one of the data points but does not represent the central tendency as the median.
*175.0 mg/dL*
- This value is incorrect because while 175 is one of the two middle numbers, the **median of an even set of numbers** is the **average of the two middle numbers**, not just one of them.
- Simply picking one of the middle numbers without averaging is a common error in determining the median for an even set.
*170.0 mg/dL*
- This value is incorrect because while 170 is one of the two middle numbers, the **median for an even set** of data points requires **averaging the two middle values**.
- It represents only the lower of the two central numbers, not the overall median.
