Lecture 4
Clinical epidemiology. Modern
principles and rules conducting of
clinical researches. Concept of
null hypothesis
Null hypothesis
The term null hypothesis was
coined by the English geneticist
and statistician Ronald Fisher.
Null hypothesis
Null hypothesis (H0) is a hypothesis (scenario) set up to
be nullified, refuted, or rejected ('disproved'
statistically) in order to support an alternative
hypothesis. When used, the null hypothesis is
presumed true until statistical evidence, in the form of
a hypothesis test, indicates otherwise — that is, when
the researcher has a certain degree of confidence,
usually 95% to 99%, that the data does not support
the null hypothesis. It is possible for an experiment to
fail to reject the null hypothesis. It is also possible
that both the null hypothesis and the alternate
hypothesis are rejected if there are more than those
two possibilities.
Null hypothesis
Let’s return to the question of whether we
(a) reject or accept the null hypothesis; and
(b) if we reject the null hypothesis, do we
accept the alternative hypothesis.
Four primary types of epidemiology studies
If our statistical analysis shows that the two
distributions are the same at the
significance level (either 0.05 or 0.01) that
we have set, we simply accept the null
hypothesis.
Alternatively, if the two distributions are
different, we need to either accept or reject
the alternative hypothesis. This will depend
on whether we made a one- or two-tailed
prediction.
Randomization
Randomization is the process of making
something random; this means:
 Generating a random permutation of a
sequence (such as when shuffling cards).
 Selecting a random sample of a population
(important in statistical sampling).
 Generating random numbers: see Random
number generation.
 Transforming a data stream using a scrambler
in telecommunications.
Other uses of randomization
Randomization is used extensively in the
field of gambling (or generally being
random). Imperfect randomization may
allow a skilled gambler to have an
advantage, so much research has been
devoted to effective randomization. A
classic example of randomization is
shuffling playing cards.
Other uses of randomization
Randomization is a core principle in the statistical
theory of design of experiments. Its use was
extensively promoted by R.A. Fisher in his book
Statistical Methods for Research Workers.
Randomization involves randomly allocating the
experimental units across the treatment groups.
Thus, if the experiment compares a new drug
against a standard drug used as a control, the
patients should be allocated to new drug or
control by a random process.
Randomization Techniques
Although historically "manual" randomization
techniques (such as shuffling cards, drawing
pieces of paper from a bag, spinning a roulette
wheel) were common, nowadays automated
techniques are mostly used. As both selecting
random samples and random permutations can
be reduced to simply selecting random
numbers, random number generation methods
are now most commonly used, both hardware
random number generators and pseudorandom number generators.
Stratification
Stratification is the building up of layers,
and can have several meanings
Social stratification, is the dividing of a
society into levels based on wealth or
power.
Stratification in archaeology is the formation
of layers (strata) in which objects are
found.
Stratification of rock layers (strata) is part of
the geologic field of Stratigraphy.
Age standardized death rate of CHD per 100,000
population in selected countries
Total
Male
Female
Scotland (1983)
192.3
283.9
124.0
Finland (1980)
176.5
283.7
101.7
Sweden (1982)
158.4
231.5
98.0
Australia (1981)
155.9
223.7
100.3
England &Wales (1982)
154.7
231.4
94.9
USA (1980)
154.6
219.7
104.1
Denmark (1982)
153.4
220.6
99.6
Canada (1982)
145.1
205.2
94.7
Italy (1980)
79.6
113.8
51.9
France (1981)
47.3
71.5
28.1
Japan (1982)
29.5
39.3
22.0
Stratification
Stratification (botany), where seeds are
pretreated to simulate winter conditions so that
germination may occur.
In logic, stratification is a layering of predicate
symbols to guarantee unique interpretations
and to avoid paradoxical definitions like
Russell's paradox.
In mathematics, Stratification has a separate
meaning as applied to manifolds, and
singularity theory, of a decomposition into
pieces with specified relationships on fitting
together.
Stratification
In music stratification is a layering of musical
texture or the independent operating of more
than one parameter simultaneously (see
auditory stream).
In meteorology, atmospheric stratification is the
division of the atmosphere into distinct layers,
each with specific properties such as
temperature or humidity.
In histology, stratified epithelium refers to
epithelium that consists of two or more layers of
epithelial cells, in contrast to simple epithelium,
which only has one layer.
“HEALTH FOR ALL”



It is an internationally recognised structure
which enables those working to improve the
health of local communities and apply Health
for All principles, to meet and share information,
research and experiences.
The Network was established in 1987. It
currently receives a grant from the Department
of Health (England).
In 1995 the Network became a Company
Limited by Guarantee in order to affiliate
formally to the World Health Organisation and
other networks. In 1997 the Network became a
registered UK charity.