STATISTICS
Definition of statistics: a scientific discipline that provides all the principles
and methods to organise, interpret and analyse data. In some occasions,
in provides these informations for the generalisation of evidence drawn fro
observed data.
Basic statistical terms:
Population: the collection of all the entities that we are taking into
consideration (people, objects, transactions,..)
Sample: the subset of units obtained after a selection of the
population.
Statistical unit: the individual member of the population that we are
interested in
Variable: the characteristics of the statistical units that we want to
analyse.
Variables can be classified as :
1) Qualitative
2) Quantitative
Qualitative variables
- Are expressed by categories
- These categories are mutually exclusive, hence no unit can be
placed in two or more categories at the same time.
- Examples: gender, hair colour, job, city of birth.
They may be: Nominal or ordinal
1. Nominal= if the categories cannot be arranged (ex: religion,
payment method…)
2. Ordinal= if the categories can be arranged (ex: army degree,
degrees of satisfaction of customers, heights…)
, Quantitative variables
- Are expressed by numbers
- Examples: salaries, expenses, number of cars
They may be: Discrete or continuous
1. Discrete= if the number of possible values is countable (ex:
household size, number of students,…)
2. Continuous= if it can take all values on intervals of real
numbers (does not necessarily have to be an integer; ex:
length, temperature …)
Percentage differences
A and B are two numbers with the same unit of measurement.
A is the reference value.
Absolute difference = B-A
Relative difference = ( B-A)/ A
Percentage difference = 100 (B-A) / A
Ratios
Given a set of quantities: a1, a2,…, ak, such that:
a1 + a2 + … + a k = A
The percentage ratio can be calculated by:
100 ( a1/A) , 100 ( a2/A) , …100 (ak/A), where each quantity is a
percentage of the total A.
Definition of statistics: a scientific discipline that provides all the principles
and methods to organise, interpret and analyse data. In some occasions,
in provides these informations for the generalisation of evidence drawn fro
observed data.
Basic statistical terms:
Population: the collection of all the entities that we are taking into
consideration (people, objects, transactions,..)
Sample: the subset of units obtained after a selection of the
population.
Statistical unit: the individual member of the population that we are
interested in
Variable: the characteristics of the statistical units that we want to
analyse.
Variables can be classified as :
1) Qualitative
2) Quantitative
Qualitative variables
- Are expressed by categories
- These categories are mutually exclusive, hence no unit can be
placed in two or more categories at the same time.
- Examples: gender, hair colour, job, city of birth.
They may be: Nominal or ordinal
1. Nominal= if the categories cannot be arranged (ex: religion,
payment method…)
2. Ordinal= if the categories can be arranged (ex: army degree,
degrees of satisfaction of customers, heights…)
, Quantitative variables
- Are expressed by numbers
- Examples: salaries, expenses, number of cars
They may be: Discrete or continuous
1. Discrete= if the number of possible values is countable (ex:
household size, number of students,…)
2. Continuous= if it can take all values on intervals of real
numbers (does not necessarily have to be an integer; ex:
length, temperature …)
Percentage differences
A and B are two numbers with the same unit of measurement.
A is the reference value.
Absolute difference = B-A
Relative difference = ( B-A)/ A
Percentage difference = 100 (B-A) / A
Ratios
Given a set of quantities: a1, a2,…, ak, such that:
a1 + a2 + … + a k = A
The percentage ratio can be calculated by:
100 ( a1/A) , 100 ( a2/A) , …100 (ak/A), where each quantity is a
percentage of the total A.
