Updated: 5/18/2019

Bias

Topic
Review Topic
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Questions
14
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0
Evidence
12
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Definition
  • A systematic error in collecting or interpreting observations
Types of Bias
  • Confounding 
    • A third factor is either positively or negatively associated with both the exposure and outcome  
    • Confounders are not in the causal pathway
      • if not adjusted for can distort true association 
      • either towards or away from the null hypothesis
  • Selection bias
    • Nonrandom selection of study participants leads to erroneous conclusions
      • e.g. if investigating the adverse events associated with a new drug, those with either the best or worst outcomes may be more likely to participate in a telephone survey about their experience with drug
  • Measurement bias
    • Information is gathered in a way that distorts the information
      • Hawthorne Effect 
        • subjects alter their behavior when they know they are being studied  
  • Recall bias
    • Subjects with the disease are more likely to recall the exposure of interest
      • e.g. parents of children with cancer recall exposure to a chemical
  • Late-look bias
    • Patients with severe disease are less likely to be studied, because they die
      • e.g. a group of HIV+ individuals are all asymptomatic
  • Procedure bias
    • Different groups not treated the same
  • Lead-time bias
    • Early detection looks like increase in survival 
      • common with improved screening
  • Pygmalion effect 
    • Investigator inadvertently conveys his high expectations to subjects, who then produce the expected result
    • A "self-fulfilling prophecy"
      • Golem Effect is the opposite: study subjects decrease their performance to meet low expectations of investigator.
  • Design bias
    • The control group is inappropriately non-comparable to the intervention group
  • Observer bias 
    • Investigator's evaluation is impacted by knowledge of exposure status
Ways to Reduce Bias
  • Randomization
    • an intention-to-treat analysis is used in order to preserve randomization 
  • Use placebo as control
  • Blind studies
    • Double blind is best
    • Double blinding means both investigators and subjects are blinded.  
  • Crossover studies 
    • Subject acts as own control
    • Limits confounding
Examples of Effects that are Not Bias
  • Effect modification
    • Effect modification occurs when a third factor affects the magnitude of the relationship between the exposure and the disease
      • e.g. The increased risk of cancer in smokers is even higher among those who also drink heavily.  
      • NOT a type of bias
  • Latent period
    • The negative effects of a disease may take years to become clinically apparent
    • NOT a type of bias
  • Generalizability 
    • the ability to use results from a study to draw conclusiosn about populations different than that used in the study
    • this is most problematic for studies that evaluate only a very specific population 
 

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Questions (14)
Lab Values
Blood, Plasma, Serum Reference Range
ALT 8-20 U/L
Amylase, serum 25-125 U/L
AST 8-20 U/L
Bilirubin, serum (adult) Total // Direct 0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca2+) 8.4-10.2 mg/dL
Cholesterol, serum Rec: < 200 mg/dL
Cortisol, serum 0800 h: 5-23 μg/dL //1600 h:
3-15 μg/dL
2000 h: ≤ 50% of 0800 h
Creatine kinase, serum Male: 25-90 U/L
Female: 10-70 U/L
Creatinine, serum 0.6-1.2 mg/dL
Electrolytes, serum  
Sodium (Na+) 136-145 mEq/L
Chloride (Cl-) 95-105 mEq/L
Potassium (K+) 3.5-5.0 mEq/L
Bicarbonate (HCO3-) 22-28 mEq/L
Magnesium (Mg2+) 1.5-2.0 mEq/L
Estriol, total, serum (in pregnancy)  
24-28 wks // 32-36 wks 30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks 40-220 ng/mL // 80-350 ng/mL
Ferritin, serum Male: 15-200 ng/mL
Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma Male: 4-25 mIU/mL
Female: premenopause: 4-30 mIU/mL
midcycle peak: 10-90 mIU/mL
postmenopause: 40-250
pH 7.35-7.45
PCO2 33-45 mmHg
PO2 75-105 mmHg
Glucose, serum Fasting: 70-110 mg/dL
2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation Fasting: <5 ng/mL
Provocative stimuli: > 7ng/mL
Immunoglobulins, serum  
IgA 76-390 mg/dL
IgE 0-380 IU/mL
IgG 650-1500 mg/dL
IgM 40-345 mg/dL
Iron 50-170 μg/dL
Lactate dehydrogenase, serum 45-90 U/L
Luteinizing hormone, serum/plasma Male: 6-23 mIU/mL
Female: follicular phase: 5-30 mIU/mL
midcycle: 75-150 mIU/mL
postmenopause 30-200 mIU/mL
Osmolality, serum 275-295 mOsmol/kd H2O
Parathyroid hormone, serume, N-terminal 230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C) 20-70 U/L
Phosphorus (inorganic), serum 3.0-4.5 mg/dL
Prolactin, serum (hPRL) < 20 ng/mL
Proteins, serum  
Total (recumbent) 6.0-7.8 g/dL
Albumin 3.5-5.5 g/dL
Globulin 2.3-3.5 g/dL
Thyroid-stimulating hormone, serum or plasma .5-5.0 μU/mL
Thyroidal iodine (123I) uptake 8%-30% of administered dose/24h
Thyroxine (T4), serum 5-12 μg/dL
Triglycerides, serum 35-160 mg/dL
Triiodothyronine (T3), serum (RIA) 115-190 ng/dL
Triiodothyronine (T3) resin uptake 25%-35%
Urea nitrogen, serum 7-18 mg/dL
Uric acid, serum 3.0-8.2 mg/dL
Hematologic Reference Range
Bleeding time 2-7 minutes
Erythrocyte count Male: 4.3-5.9 million/mm3
Female: 3.5-5.5 million mm3
Erythrocyte sedimentation rate (Westergren) Male: 0-15 mm/h
Female: 0-20 mm/h
Hematocrit Male: 41%-53%
Female: 36%-46%
Hemoglobin A1c ≤ 6 %
Hemoglobin, blood Male: 13.5-17.5 g/dL
Female: 12.0-16.0 g/dL
Hemoglobin, plasma 1-4 mg/dL
Leukocyte count and differential  
Leukocyte count 4,500-11,000/mm3
Segmented neutrophils 54%-62%
Bands 3%-5%
Eosinophils 1%-3%
Basophils 0%-0.75%
Lymphocytes 25%-33%
Monocytes 3%-7%
Mean corpuscular hemoglobin 25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration 31%-36% Hb/cell
Mean corpuscular volume 80-100 μm3
Partial thromboplastin time (activated) 25-40 seconds
Platelet count 150,000-400,000/mm3
Prothrombin time 11-15 seconds
Reticulocyte count 0.5%-1.5% of red cells
Thrombin time < 2 seconds deviation from control
Volume  
Plasma Male: 25-43 mL/kg
Female: 28-45 mL/kg
Red cell Male: 20-36 mL/kg
Female: 19-31 mL/kg
Cerebrospinal Fluid Reference Range
Cell count 0-5/mm3
Chloride 118-132 mEq/L
Gamma globulin 3%-12% total proteins
Glucose 40-70 mg/dL
Pressure 70-180 mm H2O
Proteins, total < 40 mg/dL
Sweat Reference Range
Chloride 0-35 mmol/L
Urine  
Calcium 100-300 mg/24 h
Chloride Varies with intake
Creatinine clearance Male: 97-137 mL/min
Female: 88-128 mL/min
Estriol, total (in pregnancy)  
30 wks 6-18 mg/24 h
35 wks 9-28 mg/24 h
40 wks 13-42 mg/24 h
17-Hydroxycorticosteroids Male: 3.0-10.0 mg/24 h
Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total Male: 8-20 mg/24 h
Female: 6-15 mg/24 h
Osmolality 50-1400 mOsmol/kg H2O
Oxalate 8-40 μg/mL
Potassium Varies with diet
Proteins, total < 150 mg/24 h
Sodium Varies with diet
Uric acid Varies with diet
Body Mass Index (BMI) Adult: 19-25 kg/m2
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(M1.ST.12) A new formula for an anti-wrinkle cream is being tested for efficacy in a group of 362 healthy 40- to 60-year-old female volunteers. The marketing team randomizes the volunteers. Half receive the new formula and the other half of the volunteers receive the original formula. The mean age in the test group is 48 (95% CI 42-56), and the average age of the control group is 49 (95% CI 42-55). The volunteers are unaware of which formula they receive. The research and development team then compares before and after photographs of the volunteers following 6 weeks of at home application twice daily. For simplicity, the marketing team labels the photographs with "new formula" or "original formula." 98% of volunteers in the test group complete the study, and 97% of volunteers in the control group complete the study. The researchers conclude that there is improved wrinkle reduction with 6 weeks of use of the new formula. Which of the following potential biases most likely impacted this conclusion? Review Topic

QID: 103974
1

Selection bias

3%

(1/29)

2

Hawthorn effect

10%

(3/29)

3

Observer bias

55%

(16/29)

4

Procedure bias

0%

(0/29)

5

Recall bias

3%

(1/29)

M1

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PREFERRED RESPONSE 3

(M1.ST.79) A new study is investigating the effects of an experimental drug, Exerzisin, on the duration and intensity of exercise. In the treatment group participants are given daily Exerzisin at the main treatment facility and instructed to exercise as much as they would like on the facility's exercise equipment. Due to an insufficient number of exercise units at the main treatment center, the control subjects are given free access to an outside, private gym. The duration and intensity of exercise in both groups is measured with a pedometer. The perspicacious undergraduate, hired to input all the data, points out that the treatment group may be more motivated to exercise harder and longer because their exercising can be observed by the investigators. To which form of bias is he alluding? Review Topic

QID: 103896
1

Selection bias

8%

(6/72)

2

Hawthorne effect

69%

(50/72)

3

Recall bias

1%

(1/72)

4

Pygmalion effect

10%

(7/72)

5

Lead time bias

1%

(1/72)

M1

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PREFERRED RESPONSE 2
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(M1.ST.66) Study X examined the relationship between coffee consumption and lung cancer. The authors of Study X retrospectively reviewed patients' reported coffee consumption and found that drinking greater than 6 cups of coffee per day was associated with an increased risk of developing lung cancer. However, Study X was criticized by the authors of Study Y. Study Y showed that increased coffee consumption was associated with smoking. What type of bias affected Study X, and what study design is geared to reduce the chance of that bias? Review Topic

QID: 104072
1

Observer bias; double blind analysis

17%

(9/54)

2

Lead time bias; placebo

0%

(0/54)

3

Selection bias; randomization

7%

(4/54)

4

Measurement bias; blinding

0%

(0/54)

5

Confounding; randomization or crossover study

65%

(35/54)

M1

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PREFERRED RESPONSE 5

(M1.ST.18) A pharmaceutical company conducts a randomized clinical trial in an attempt to show that their new anticoagulant drug, Aclotsaban, prevents more thrombotic events following total knee arthroplasty than the current standard of care. However, a significant number of patients are lost to follow-up or fail to complete treatment according to the study arm to which they were assigned. Despite this, the results for the patients who completed the course of Aclotsaban are encouraging. Which of the following techniques is most appropriate to use in order to attempt to prove the superiority of Aclotsaban? Review Topic

QID: 102597
1

Per-protocol analysis

6%

(2/32)

2

Intention-to-treat analysis

16%

(5/32)

3

As-treated analysis

41%

(13/32)

4

Sub-group analysis

9%

(3/32)

5

Non-inferiority analysis

6%

(2/32)

M1

Select Answer to see Preferred Response

PREFERRED RESPONSE 2

(M1.ST.24) A new antihypertensive medication is studied in 3,000 Caucasian men with coronary heart disease who are over age 65. The results show benefits in terms of improved morbidity and mortality as well as a decreased rate of acute coronary events with minimal side effects. After hearing about this new medication and supporting study at a recent continuing education course, a family physician elects to prescribe this medication to a 39-year-old Hispanic female who presents with primary hypertension. After a one month trial and appropriate adjustments in the dosing, the patient's blood pressure is not well controlled by this medication. Which of the following statistical concepts could explain this patient's poor response to the medication? Review Topic

QID: 104030
1

Confounding

8%

(3/39)

2

Selection bias

46%

(18/39)

3

Effect modification

0%

(0/39)

4

Generalizability

28%

(11/39)

5

Observer bias

8%

(3/39)

M1

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PREFERRED RESPONSE 4

(M1.ST.21) A study is funded by the tobacco industry to examine the association between smoking and lung cancer. They design a study with a prospective cohort of 1,000 smokers between the ages of 20-30. The length of the study is five years. After the study period ends, they conclude that there is no relationship between smoking and lung cancer. Which of the following study features is the most likely reason for the failure of the study to note an association between tobacco use and cancer? Review Topic

QID: 106094
1

Effect modification

6%

(8/131)

2

Latency period

52%

(68/131)

3

Pygmalion effect

8%

(10/131)

4

Late-look bias

14%

(18/131)

5

Confounding

16%

(21/131)

M1

Select Answer to see Preferred Response

PREFERRED RESPONSE 2

(M1.ST.4022) Two studies are reviewed for submission to an oncology journal. In Sudy 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? Review Topic

QID: 107007
1

Lead time bias; Pygmalion effect

40%

(10/25)

2

Lead time bias; Golem effect

8%

(2/25)

3

Latency bias; Pygmalion effect

20%

(5/25)

4

Latency Bias; Golem effect

4%

(1/25)

5

Confounding; Golem effect

4%

(1/25)

M1

Select Answer to see Preferred Response

PREFERRED RESPONSE 1

(M1.ST.80) A randomized controlled trial is conducted investigating the effects of different diagnostic imaging modalities on breast cancer mortality. 8,000 women are randomized to receive either conventional mammography or conventional mammography with breast MRI. The primary outcome is survival from the time of breast cancer diagnosis. The conventional mammography group has a median survival after diagnosis of 17.0 years. The MRI plus conventional mammography group has a median survival of 19.5 years. If this difference is statistically significant, which form of bias may be affecting the results? Review Topic

QID: 103897
1

Selection bias

6%

(3/51)

2

Misclassification bias

2%

(1/51)

3

Lead-time bias

57%

(29/51)

4

Recall bias

4%

(2/51)

5

Because this study is a randomized controlled trial, it is free of bias

18%

(9/51)

M1

Select Answer to see Preferred Response

PREFERRED RESPONSE 3

(M1.ST.3) An office team is being observed by an outside agency at the request of management to make sure they are completing all their tasks appropriately. Several of the employees are nervous that they are being watched and take care to perform their jobs with extra care, more so than they would have done during a normal workday. What best describes this behavior? Review Topic

QID: 104009
1

Pygmalion effect

0%

(0/15)

2

Novelty effect

0%

(0/15)

3

Observer bias

20%

(3/15)

4

Hawthorne effect

53%

(8/15)

5

Ringelmann effect

0%

(0/15)

M1

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PREFERRED RESPONSE 4
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(M1.ST.83) You are reviewing the protocol for a retrospective case-control study investigating risk factors for mesothelioma among retired factory workers. 100 cases of mesothelioma and 100 age and sex matched controls are to be recruited and interviewed about their exposure to industrial grade fiberglass by blinded interviewers. The investigators' primary hypothesis is that cases of mesothelioma will be more likely to have been exposed to industrial grade fiberglass. The design of this study is most concerning for which type of bias? Review Topic

QID: 103900
1

Interviewer bias

7%

(2/27)

2

Recall bias

67%

(18/27)

3

Observer bias

11%

(3/27)

4

Lead-time bias

0%

(0/27)

5

This study design is free of potential bias

7%

(2/27)

M1

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PREFERRED RESPONSE 2
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Topic COMMENTS (37)
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