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Biostatistics - ConceptsTudor Calinici – JPEMS 2014
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Based on the researchers role Observational Experimental
Study types
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Description of a health phenomenon
Evaluation of a diagnostic test
Evaluation of a therapeutic approach
Evaluation of prognostic (risk or protective) factors
Main domains of medical research
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Based on study objectives Descriptive Analytical
Types of studies
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Descriptive
Inferential
Statistics
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Based on the studied population Exhaustive Sampling
Study types
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Population
Sample / representative sample
Statistical objects
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Population vs. Sample
Use sample because size accessibility Economical reasons Financial reasons
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Representative sample
A good sample must provide an image about the population
Representative sample quantitative condition qualitative condition
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Representative sample
Exposed – non-exposed
Case - control
Types of samples - groups
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Based on the duration of data collection Cross-sectional • longitudinal - retrospective or prospective
Study types
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Collecting data
Descriptive statistics
Characteristics – Variables Quantitative; Qualitative
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To present data Tables Charts Numeric characteristics
Descriptive statistics
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Tables
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Frequency tables
Count of Gender
Treatment Total
Metistatin 584
Placebo 614
Grand Total 1198
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Gender
Treatment f mGrand Total
Metistatin 293 291 584
Placebo 321 293 614
Grand Total 614 584 1198
Contingency tables
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The representation of the data
Distribution
For frequency tables For contingency tables
Charts
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A randomized clinical trial (RCT) has been performed in order to test the efficacy of Metistatin (a statin - drug intended to lower blood cholesterol levels) versus Placebo for preventing major vascular events (nonfatal myocardial infarction, cardiac death, stroke) in diabetic patients.
A number of 1198 patients with diabetes from several hospitals in
England were included in the study sample. The study was conducted after the approval for marketing of this
preparation. .
Problem
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Of interest for the study was whether Metistatin is superior to placebo (placebo - identical in appearance, size, taste to Metistatin, but lacking the active substance) in preventing major vascular events. A secondary objective has been to follow if Metistatin lowers cholesterol more than Placebo. Another question was “Is gender related to major cardiovascular events?”
Every patient who entered the study was randomly allocated to
one of two preparations: Metistatin 80 mg daily administered as a single dose, or placebo. The allocation of the two interventions was masked – the investigator was allocating for each eligible patient a code corresponding to one of the two interventions, found in opaque numbered sealed envelopes. The pharmacy of the hospital was making sure each patient would receive the correct intervention based on the codes.
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Neither the patients nor the physicians were aware about which intervention the patients were receiving.
Subjects were followed under similar care
circumstances for all diabetic patients from the respective hospitals.
The study excluded subjects receiving other
medications that alter cholesterol levels (prednisone, estrogen, progesterone, anabolic drugs, and cyclosporine), subjects allergic to Metistatin, obese subjects and subjects for whom transportation for follow-up would be difficult or impossible. Also, all subjects who entered the study signed an informed consent (the act by which the patient consents to enter the study, acknowledging their rights, all the risks and benefits posed by his/her participation in the study).
Patients were followed for 10 years. Blood cholesterol levels were measured at the beginning and at the end of the study and the occurrence of major vascular events has been recorded
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Describe the data collected in BD_Ten.xls file according to:
Gender Treatment Major vascular event Treatment by gender Major vascular event by gender
Exercise 1
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Central Measures Mean, median, mode
Spread Measures Range, Standard Deviation, Coefficient of
variation
Quantitative characteristics
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Sqew
Kurt
Normal distribution
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Prevalence Incidence
Ratios Odd Ratio Risk Ratio
Qualitative characteristics
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For qualitative variables compute the central measures, spread measures and decide if the data are normal distributed
Exercise 2
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Qualitative variablesChi Square test
Quantitative variablesT test for means
Inference
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Define research questions in terms of statistical hypothesis?
Respond to the research questions!
Exercise