Medical Statistics
Introduction:Medical Statistics: Is an ill defined subject .it has topics in common with demography, epidemiology, microbiology, clinical chemistry, pathology, anatomy, community medicine, genetics & may other subjects. or data are concerned with medical & biological information.
Definitions:
1. Statistics: Is the science of collecting, summarizing, presenting & analyzing data. This analysis may lead to conclusion & subsequent decision or2. Statistics: May be defined as the science concerned with treatment of numerical data derived from group of individuals, these individuals will often be people e.g:(those suffering from certain disease ,or those living in a certain area, or they may be animals or other organism). (Armitage)
Statistics: Is divided it to two parts:
Descriptive statistics: Dealing with methods for organizing a large mass of data, may be:Tabular, diagrammatic or numerical.
Inferential statistics: Dealing with methods that enable a conclusion to be drawn from that data. (Analytic statistics)
Population: A large mass or group of data which can be finite or infinite.
Finite population: Any finite collection of observation of unit e.g: (no. of babies born in Iraq in 2012).Sample: Is a part of population (subset) which tells the investigator about the population e.g: (no. of babies born in Mosul city in 2012).
Because of chance, different samples give different results and this must be taken into account when using a sample to make inferences about the population, this phenomenon is called Sampling Variation.
Variable & Constant:
Variable: This is a quantity which varies such that it may take any one of specified set of values. It may be:Measurable, e.g:( systolic blood pressure (mmHg)). or Non measurable, e.g: (sex (M,F)).
Variables may be further sub-classified according to their scale of measurement.
1. Qualitative: A categorical variable, non numerical or non measurable. e.g: ( race, sex, bd.gr., place of birth, education, hair color, eyes color ….etc). It may be:* Nominal: (classificatory) e.g: blood group (A,B,AB,O), sex (male, female).
* Ordinal: (ranking) scale e.g: education (illiterate, primary, secondary,…etc), Social class (1st, 2nd, 3rd, 4th, 5th)).
2. Quantitative: A numerical or measurable variable which may be taking some values it may be:
*Discrete:(Discontinuous) Taking some values in a discontinuous set of values. e.g: (integers, age, no. of bacteria, parity ,no. of patients,….etc).
*Continuous: Taking some values in an infinity devisable range of values. e.g: ( exact age, height, weight, uric acid level, blood pressure,….etc).
8 Variable QualitativeQuantitative(non measurable)(measurable)e.gSexBd. groupPlace of birthHair color…etce.gAgeNo. of bact.Integers…etce.gExact age HeightWeight Uric acid levelBlood pressure …etc Discrete( discontinuous )( Continuous ) Noninal Ordinale.gEducationSocial class…etc
Symbols: Summation Notation
Variable (Real variable) is a symbol denotes
Xi a particular variable (age, height, weight,...etc).
Dummy variable(Suffix or Index or Subscript)
Where: i = 1,2,3,….etc…..,n
n = sample size = no. of events
= no. of observation = no. of reading.
The Real variable taking any capital letter from A–Z (e.g: X, Y, Z )
The Dummy variable taking any small letter from a-z (e.g: i, j, k )10