Central Limit Theorem

Central Limit Theorem
Definition
The Central Limit Theorem is a statement about the
characteristics of the sampling distribution of means of
random samples from a given population. That is, it
describes the characteristics of the distribution of values
we would obtain if we were able to draw an infinite
number of random samples of a given size from
a given population and we calculated the mean of each
sample. The Central Limit Theorem consists of three
statements: 1) the mean of the sampling distribution
of means is equal to the mean of the population from
which the samples were drawn, 2) the variance of the
sampling distribution of means is equal to the variance
of the population from which the samples were drawn
divided by the size of the samples and 3) if the original
population is distributed normally, the sampling distribution
of means will also be normal. If the original population
is not normally distributed, the sampling distribution
of means will increasingly approximate a normal
distribution as sample size increases (i. e. when increasingly
large samples are drawn).

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Bottom-Up Approach (For Cost-Estimation)

Definition
In a bottom-up approach the costs are collected directly from patients suffering from a defined disease. The figures from those patients are extrapolated to represent the whole population by using national prevalence figures.

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Biostatistical Design

Biostatistical Design
Definition
Biostatistical design is a unified approach to a common
core of problems of statistical design that are central to
many related fields in the biomedical sciences, in the
health sciences, in the social sciences and in health services
research led by three fundamental principles: 1)
all problems occur in a system of interconnected processes,
2) variation exists in all processes, and 3) understanding
and reducing variation are the keys of success.
It covers at least the following elements: identification
of the data to be collected (this includes the variables to
be measured, their role in a study, ways of measurement,
the number of experimental units, namely, the
size of the study, and the way they were chosen and
followed-up); the design of a comparison/relationship
strategy; an appropriate analytic model for describing
and processing data; and a list of questions to be
answered throughout the study (What inferences does
one hope to make from the study? What conclusions
might one draw from the study? To what population(s)
is/are the conclusion(s) applicable)?

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Autochthonous Population

Autochthonous Population
Synonyms
Natives; Original inhabitants
Definition
Autochthonous population is a general and more neutral
term for natives or original inhabitants of a country
or region. The term ‘autochthonous’ is used to avoid
static ideas implied in terms like ‘native’ or ‘original’.
The terms ‘allochthonous’ population and ‘immigrants’
can be seen as synonyms. The difference between
autochthonous and allochthonous populations is not
absolute – it is a relative one. The difference depends
on both context and time, combined with a range of
variables (e. g., ideas of origin, legal status, social inclusion
and status, ethnic or racial background, religion) in
a specific national or regional context.

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Attributable Risk (AR)

Attributable Risk (AR)
Definition
Attributable risk (AR) is the proportion of the incidence
of a disease in exposed individuals that is due to exposure.
It is the incidence of a disease in the exposed
population that would be eliminated if exposure were
eliminated. It can be calculated as rate difference (the
rate in the exposed group minus the rate in the unexposed
group) or risk difference (the difference between
the risks in the exposed and unexposed groups). When
the level of risk in both exposed and unexposed groups
is the same, the risk difference is 0. If an exposure is
harmful (e. g., cigarette smoking), the risk difference is
expected to be greater than 0. If an exposure is protective
(e. g., vaccine), the risk difference will be less
than 0.
The AR is sometimes referred to as attributable risk in
exposed individuals because it is used to quantify the
risk that can be attributed to exposure in the exposed
group. The AR is the measure of association that ismost
relevant when making decisions for individuals.
Attributable risk percent (AR%) is the percent of the
incidence of a disease that is due to exposure in exposed
individuals. It is the percent of the incidence of a disease
in the exposed population that would be eliminated
if exposure were eliminated.

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Association Studies

Association Studies
Definition
The association studies approach is based on showing
a higher or lower  allele frequency among cases
and controls, candidate genes presumed to include
the disease-causing alleles are then studied. Although
two types of genetic association studies are described
(family- and population-based), the rationale is similar,
ascertainment of mutation related to disease risk
in genomic screening by identification chromosomal
regions shared by patients.

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Allele

Allele
Synonyms
Allelomorph
Definition
Diploid organisms like humans carry two copies of each
autosomal chromosome (paired homologous chromosomes)
and thus, also two copies of every autosomal
gene. One of the paired chromosomes (one of the two
copies of a gene) of an individual is transmitted by the
father, the other by the mother. The sequence (order of
base pairs) of the two copies of a gene does not have to
be completely identical due to normal variation (polymorphisms)
or  mutations. Alleles are the different
(alternative, non-identical) forms of a gene or DNA
sequence at a specific genomic/chromosomal position
(locus). An individual can only possess two alleles at
each specific position on a pair of homologous chromosomes,
but a group or population may contain a lot of
different alleles at a certain locus.

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Adjusted Rates

Adjusted Rates
Definition
Adjusted rates are summary measures of the rate of
morbidity or mortality in a population in which statistical
procedures have been applied to remove the effect of
differences in composition of the various populations.
There are two methods for the adjustment of rates: the
direct method and the indirect method. Direct and indirect
refer to the source of the rates.
Cross-References
 Standardized Rate

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The of Vitamin Rich Shampoos that you Must Know

“Buy this shampoo for your 100% dandruff free hair.” Is that right? Such common advertising spiel for marketers on the kind of shampoo they sell to the public. But have you thought of the reality of these spiels? Or have you tried using their products to increase your hair´s health and vibrancy?

While it´s true that there are many shampoo manufacturers that claim superiority over the other, knowing which shampoo could bring out the best in your hair is such difficult to find out. So if you´re on the search for the best shampoo for your healthy hair, think the “what” of these ads and check how the products could generate greater results for your hair. Yes, it´s undeniable that all marketing companies would claim their best for their products so be cautious. Be a critical consumer and pick the best. Remember, your hair is your crown of beauty so that means, extreme care is needed.

The truth is that there are four main problems that vitamin-infused shampoos are meant to cure:

Vitamins in shampoos are supposed to halt slow growth of your hair, graying of hair, hair loss, and general loss of health of your hair.

Vitamin-infused shampoos can either have a specific vitamin or multivitamins in their solution, some herbal supplements or a special ingredient known only to the manufacturer but which they say is a winner of a substance. Sometimes, you may see some famous names in the hairstyling world endorsing a specific shampoo which they claim is THE best in the market. All these choices can leave an ordinary consumer bewildered. So what is the truth?

Vitamins in shampoos can leave your scalp and hair healthier through repeated use. There is an issue on this claim actually. The truth is that most of the manufacturers of these shampoos rely on testimonials from “satisfied users” to back up their claim. Testimonials are not automatically false, but to provide conclusive proof that a claim is true for a certain population of people, controlled studies have to be done so that controlled results can be produced. If you had to choose between believing a testimonial from a “satisfied user” known only by her initials, and a controlled study done by a reputable testing center, which would you believe? Obviously, the later, right?

No conclusive evidence that vitamins applied externally to your hair via a shampoo will restore the health of your hair. It is generally accepted in medical circles that a lack of appropriate nutrition in your body can change the health of your hair for the worse. However, to claim that applying vitamins directly on the hair will bring back health and vitality to your hair is not based on any body of firm scientific evidence at present.

With the abovementioned 4 issues, a scientific fact does exist which puts doubt on the claim that vitamin-enriched shampoos can produce healthier hair –that hair is already dead when it shoots up out of our scalp. That is why when you have a haircut you cannot feel pain – there are no nerve endings connecting your hair shaft to your body anymore. For this reason, some scientific experts doubt very much that vitamin-enriched shampoos are absorbed by your hair, and make the hair and scalp healthier through continuous use. Last word of advice is for you to visit a doctor when you have hair issues.

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Getting the energy you need

Energy. It propels the basketball player to endure the game, score points, and win. It helps the busy executive reach his or her desired goals and cope with hectic schedules almost effortlessly. It turns the plain homemaker into a Super Mom to take care of her home and family. It enables the student to meet the demands of school. It gives people that extra edge to succeed in all levels. Continue Reading…

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