Updated: 1/20/2019

Types of Studies

Topic
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Questions
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Evidence
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Case-Control Study
  • Observational (by definition)
  • Retrospective (almost always)
  • Compares the odds of being exposed between patients with disease and patients without the disease
    • e.g. Patients with cirrhosis are more likely to have been exposed to heavy alcohol use
  • Odds Ratio (OR) is measure of disease association
    • OR = (a/b) / (c/d) = ad/bc   
Cohort Study
  • Observational (by definition)
    • Can be either prospective or retrospective
  • Compares a group with a given risk factor to a group without the risk factor to see if there is an increased likelihood of developing disease  
    • e.g. Patients who drink alcohol are more likely to get cirrhosis
  • Relative Risk (RR) is measure of disease association 
    • asks, "How much more likely are you to get cirrhosis if you drink alcohol?"
    • RR = [a/(a+b)] / [c/(c+d)]
Cross-Sectional Study
  • Observational 
  • Determines disease status and exposure/risk factor status at the same point in time
    • can show association but not causality
  • measures disease prevalence 

Factorial design study 

  • Randomizes patients into different interventions with 2 or more variables being studied in each intervention 
Crossover Study
  • Participants alternate receiving intervention and placebo
  • Participants act as own controls 
    • improves power and precision of study
    • all patients receive intervention
Twin concordance study
  • Compares monozygotic and dizygotic twins to measure disease heritability
Adoption study
  • Compares siblings raised by biologic and adoptive parents to measure influence of environmental vs inherited factors
Meta-analysis
  • Combines data from multiple studies 
    • better precision than individual studies
    • improves generalizability of study findings
    • considered to be the highest level of clinical evidence
    • limited by:
      • quality of individual studies
      • bias in study selection
Case series
  • Report on observations of patients with known exposure or disease 
  • Does not have comparison group so cannot perform hypothesis testing 
 

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Questions (12)
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.20) A recent study attempted to analyze whether increased "patient satisfaction" driven healthcare resulted in increased hospitalization. In this hospital, several of the wards adopted new aspects of "patient satisfaction" driven healthcare, whereas the remainder of the hospital continued to use existing protocols. Baseline population characteristics and demographics were collected at the start of the study. At the end of the following year, hospital use was assessed and compared between the two groups. Which of the following best describes this type of study? Review Topic

QID: 102599
1

Retrospective cohort

20%

(25/124)

2

Prospective cohort

38%

(47/124)

3

Retrospective case-control

18%

(22/124)

4

Prospective case-control

8%

(10/124)

5

Cross-sectional study

12%

(15/124)

M1

Select Answer to see Preferred Response

PREFERRED RESPONSE 2
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(M1.ST.18) A researcher interested in the relationship between vaccination and autism sends a survey to parents of children who are active patients at a large primary care practice. The survey asks several questions, including whether their children received their childhood vaccines on-time, and whether their children currently have a diagnosis of an autism spectrum disorder. Which of the following correctly identifies the study design used by the researcher? Review Topic

QID: 104024
1

Cross-sectional

57%

(17/30)

2

Case-crossover

7%

(2/30)

3

Cohort

20%

(6/30)

4

Randomized controlled trial

0%

(0/30)

5

Case-control

10%

(3/30)

M1

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PREFERRED RESPONSE 1

(M1.ST.10) You would like to conduct a study investigating potential risk factors that predispose patients to develop cirrhosis. Using a registry of admitted patients over the last 10 years at your local hospital, you isolate all patients who have been diagnosed with cirrhosis. Subsequently, you contact this group of patients, asking them to complete a survey assessing their prior exposure to alcohol use, intravenous drug abuse, blood transfusions, personal history of cancer, and other medical comorbidities. An identical survey is given to an equal number of patients in the registry who do not carry a prior diagnosis of cirrhosis. Which of the following best describes the type of study you are attempting to conduct? Review Topic

QID: 104016
1

Cohort study

0%

(0/12)

2

Meta-analysis

0%

(0/12)

3

Case-control study

83%

(10/12)

4

Cross-sectional study

17%

(2/12)

5

Randomized controlled trial

0%

(0/12)

M1

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PREFERRED RESPONSE 3

(M1.ST.13) A new study shows a significant association between patients with a BMI >40 and a diagnosis of diabetes (odds ratio: 7.37; 95% CI 6.39-8.50) compared to non-diabetic patients. Which of the following hypothetical studies most likely yielded these results. Review Topic

QID: 103975
1

A study consisting of 1000 non-diabetic subjects; 500 patients with a BMI > 40 and 500 patients with normal BMI, followed for diagnosis of diabetes over their life time

22%

(6/27)

2

A study consisting of 500 patients with diabetes and 500 patients without diabetes comparing BMI of subjects in both groups

48%

(13/27)

3

A study consisting of 1000 genetically similar mice; 500 randomized to diet to maintain normal weight and 500 randomized to high caloric intake with the outcome of diabetes rates in both groups after 1 year

0%

(0/27)

4

A study of 1000 patients with BMI > 40 with diabetes; 500 randomized to inpatient diet and exercise with goal BMI <25, and 500 randomized to no treatment with an outcome of glycemic control without medication after 1 year

0%

(0/27)

5

A study of 1000 patients comparing rates of diabetes diagnoses and BMIs of diabetic and non-diabetic patients

22%

(6/27)

M1

Select Answer to see Preferred Response

PREFERRED RESPONSE 2
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