Nina Globa, Master in Public Health Management, lecturer

Statistical totality, unit of observation, statistical sighsThe Relative indicators: rates; ratios; proportionsThe measures of central tendency: arithmetic mean, average; mode; median Appreciation of the authenticity (correctness, accuracy) of the relative and mean indicators

Statistics is a universal science that deals with the study of the quantity of all phenomena from society and nature.Biostatistics is a social science that studies the quantitative parts of health phenomena in correlation with their qualitative parts in concrete conditions of space and time

Biostatistics has two important features:Study of mass phenomena, not particularlyStudying phenomena in concrete conditions of space and time

Historical MathematicalStatisticalEpidemiologicalSociologicalPsychologicalExperimentalEconomic etc.

Direct observational method (objective examination, percussion, palpation, auscultation) Extracting information from an official statistical forms (clinical observation sheet, ambulatory sheet etc.)Investigational method (X-ray examination, level of hemoglobin and leucocytes etc.)Monographs (books with scientific results of somebody research) Census of population

Material processing is done by checking and then by grouping

Checking can be of 2 types:QuantitativeQualitative Grouping the information is grouped in qualitative characteristics (sex, profession, place of residence) and quantitative, numerical characteristics (age, height, weight)

A group that includes a great number of things, objects, called elements (units of observation), relatively homogeneous, taken together on the basis of common factor in the boundaries of space and time and serves as a sample.

Types of statistical totality. There are:General (integral) statistical totality (N)Partial statistical totality (sample, n)

General (integral) Statistical Totality (N) is the summarizing of all observation units, according to the purpose of the study, which a possible in specific boundaries of space and time.Partial Statistical Totality (sample, n) is including a part of integral totality chosen on the selection and integration and is representative for the selection integration

The requirements for the PST are:To have available the basic characteristic features of the integral one:To have a sufficient number of observations.

Is the primary element of statistical totalityThe number of unit of observation determines the volume of destined density.Observation units characteristics are called signs.

Depending on characters or expressions can be:

Attributive (qualitative, descriptive)Numerical (quantitative)Depending on mod of influence:

Factorial sighs are sighs under whose influences change other sighsResult sighs reproduce those results and are changed under the influence of factorial sighs

Quantitative characteristics can be:

Continuous take any value (even decimal)Discontinuous take the appearance of fixed values, usually of integer numbers (ex. Number of the children in a family)Qualitative characteristics may be:

Nominal with a natural ordination of categories (ex. gender: male & female)Ordinal with a simple ordination of categories (ex. Level of education, results of treatment)

The statistical data obtained during the research express individual or group proprieties that usually are presented using absolute values, which are difficult to assess, because there are missing comparison elements and are used for analyzing very rarely phenomena.For a correlative interpretation, comparative of sighs, groups of sighs, and based of them integral totality, relative values and average, mean values are used

Absolute - which is measured in the unit of measure of the characteristics (kg, cm, km)Relative: rates; ratios; proportionsThe measures of central tendency: arithmetic mean, average; mode; median

All the relative indicators are based on the same formula: x/y x 10 , where n could be 1, 10, 100, 1000, 10000, 100000.Ratio is used to compare the occurrence of a variable in two different groupsUsually there are two completely independent groups. If one this group is included in the other, this ratio is called a proportion It is expressed in numbers(1/1; 1,2/1) or coefficients( %, (ex. female / male is 14 to 10)

Determine the quantitative distribution of the totality of components to their total the structure.

A type of ratio, in which x is part of y.

Is usually expressed in percentages

Rates measure the occurrence of an event in a population over timeThe basic formula for a rates is

number of cases occurring during a given time period x10 Rate = _________________________________________________________ population at risk during the same period

Are always specific to a particular population. They reflect grouping of people based on time, place and person.Time: year, month, week, day or hour;Place: country, state, city, school, institution;Person: age, sex, profession etc.

Ratios, proportions and rates are used to describe morbidity and mortality.

Measure the middle of the distribution of a numerical variable. is calculated dividing the sum () of the individual data (x) by the number of observations (n) , when n

Mode is a value that occurs most frequently in data set.

Ex.: 3,4,5,6,6,6,7,8,9, Mo=6. There is no mode if all values are different.May be more than one mode: bimodal or multimodal. Mode is not used frequently in practice.

The median divides the ordered array into two equal parts. The median is the middle point in the observation data set, then a half of observations are smaller and half are larger.

The median is less sensitive to extreme values than the mean is.

Before to calculate median you have to arrange the observations from smallest to largest or vice-versa

If an odd number of observations, the median Md will be the (n+1)/2 observation.

If an even number of observation, the median Md will be the midpoint between the middle two observations. Ex.: Median of 14 observations is the midpoint between 7th and 8th.

When talking about the authenticity level of the indicators is understood to their imagined reality of the phenomenon in the integral totalityTo appreciate the authenticity of the research means to determine with what probability the results gained can transferred from a selective totality to the integral totality

The standard error (average error) of the relative values and of the arithmetic mean.

The limits of confidence

The authenticity of divergence between the two values after t student test

The authenticity of divergence of groups compared by the X - test

To determine it is used the following formula

m (SEp) = (p x q : n)m = (p x q : (n-1)), if n 120

p relative indicator (ex.: rates, proportion)q the difference between the multiplier (100, 1000, 10000 etc.) and the value of the relative indicatorn - number of causes under observation

The authenticity of the arithmetic mean is determined using the arithmetic mean error, which is calculated as:

SEm = EsM = n 120 n n -1

SEm - standard error - standard deviation n- frequency of causes

The size of the error shows with the value of the obtained result by the selective survey differs from the potential one that we have in general totality. Thus we can determine the boundaries of trust and the maximum and minimum limits

The formula is:

Mgen = Msel t x m;Where:Mgen general totality meanMsel - selective totality meanm - arithmetic mean errort - accuracy criterion

With the help of students t test we can present the selective results of the outside limits for the arithmetic mean in the general totality with different kind of probabilities (p)

t=1 p = 68,26%t=2 p = 95,45%t=3 p = 99,73%

(M1 M2) (P1 - P2)t = t =

(SEM12 + SE M22 ) (SEP12 + SE P22 )

This "t" is called "t - calculated".

If the value of calculate t 1.96, then between comparable values there is a significant difference, which is estimated with a probability of 95%;If t 3, the difference between the values is significant with a probability of 99%;If t is less than 1.96, between comparable values the isnt a significant difference

Thanks for your attention!!!