Transcript Slides 5

Biostatistics - Concepts
Tudor Calinici – JPEMS 2014
Study types
 Based on the researchers role
 Observational
 Experimental
Main domains of medical research
Description of a health phenomenon
Evaluation of a diagnostic test
Evaluation of a therapeutic approach
Evaluation of prognostic (risk or protective) factors
Types of studies
 Based on study objectives
 Descriptive
 Analytical
Statistics
 Descriptive
 Inferential
Study types
Based on the studied population


Exhaustive
Sampling
Statistical objects
 Population
 Sample / representative sample
Population vs. Sample
 Use sample because




size
accessibility
Economical reasons
Financial reasons
Studies
Source: www.socialresearchmethods.net
Representative sample
 A good sample must provide an image about the
population
 Representative sample
 quantitative condition
 qualitative condition
Types of samples - groups
 Representative sample
 Exposed – non-exposed
 Case - control
Study types
Based on the duration of data collection

•
Cross-sectional
longitudinal - retrospective or prospective
Descriptive statistics
 Collecting data
 Characteristics – Variables
 Quantitative; Qualitative
Descriptive statistics
 To present data
 Tables
 Charts
 Numeric characteristics
Tables
Frequency tables
Count of Gender
Treatment
Total
Metistatin
584
Placebo
614
Grand Total
1198
Contingency tables
Gender
Treatment
f
m
Grand Total
Metistatin
293
291
584
Placebo
321
293
614
Grand Total
614
584
1198
Charts
 The representation of the data
 Distribution
 For frequency tables
 For contingency tables
Problem
 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.


 .
 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.
 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 followup 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).
Exercise 1
 Describe the data collected in BD_Ten.xls file
according to:





Gender
Treatment
Major vascular event
Treatment by gender
Major vascular event by gender
Quantitative characteristics
 Central Measures
 Mean, median, mode
 Spread Measures
 Range, Standard Deviation, Coefficient of variation
Normal distribution
 Sqew
 Kurt
Qualitative characteristics
 Prevalence
 Incidence
 Ratios
 Odd Ratio
 Risk Ratio
Exercise 2
 For qualitative variables compute the central
measures, spread measures and decide if the data are
normal distributed
Inference
Qualitative variables
Chi Square test
Quantitative variables
T test for means
Exercise
 Define research questions in terms of statistical
hypothesis?
 Respond to the research questions!