4 Types Of Data
Qualitative Data 

Quantitative Data 
Nominal data 

Discrete data 
Ordinal data 

Continuous data 
Ratio, Proportion, and Rate
RatioA ratio is the relative magnitude of two quantities or a comparison of any two values. It is calculated by dividing one interval or ratioscale variable by the other. The numerator and denominator need not be related. Therefore, one could compare apples with oranges or apples with number of physician visits.
ProportionA proportion is the comparison of a part to the whole. It is a type of ratio in which the numerator is included in the denominator. You might use a proportion to describe what fraction of clinic patients tested positive for HIV, or what percentage of the population is younger than 25 years of age. A proportion may be expressed as a decimal, a fraction, or a percentage.
RateIn epidemiology, a rate is a measure of the frequency with which an event occurs in a defined population over a specified period of time. Because rates put disease frequency in the perspective of the size of the population, rates are particularly useful for comparing disease frequency in different locations, at different times, or among different groups of persons with potentially different sized populations; that is, a rate is a measure of risk. 
Tables & Graphs
Tables 
Graphs 
Line listing, Frequency distribution 
Bar chart, pie chart, Histogram, Epidemic curve, Box plot, Twoway (or bivariate) scatter plot, Spot map, Area map, Line graph 
Numerical Methods
Measures of central tendency 
Measures of dispersion 
Measures of central tendency refer to ways of designating the center of the data. 
Also called the spread or variability, are used to describe how much data values in a frequency distribution vary from each other and from the measures of central tendency. 
Mean, Median, Mode 
Range, Interquartile range, Variance, Standard deviation, Coefficient of variation, Empirical rule,Chebychev’s inequality 


Crude and Ageadjusted Rates
Crude Rates 
AgeAdjusted Rates 
Standardized Morbidity 
Rates allow for fairer comparisons between geographies with different population totals. Crude rates also account for the total burden of a health outcome to a community. This statistic is calculated as the number of events (numerator) divided by the population at risk (denominator). The population at risk is “a term applied to all those whom an event could have happened, whether it did or not.” For many health statistics, the denominator is simply the population total. 
Age adjusting rates is a way to make fairer comparisons between groups with different age distributions. For example, a county having a higher percentage of elderly people may have a higher rate of death or hospitalization than a county with a younger population, merely because the elderly are more likely to die or be hospitalized. (The same distortion can happen when comparing races, genders, or time periods.) Age adjustment can make the different groups more comparable. 
In situations where agespecific rates are unstable because of small numbers or some are simply missing, ageadjustment is still possible using the indirect method SMR = 1 The healthrelated states or events observed were the same as expected from the agespecific rates in the standard population. SMR > 1 More healthrelated states or events were observed than expected from the agespecific rates in the standard population. SMR < 1 Less healthrelated states or events were observed than expected from the agespecific rates in the standard population. 
Two Methods for Calculating Age adjusted Rates
Direct 
Indirect 
Calculate the agespecific mortality rates for each age group in each population. Then choose the standard (reference) population from one of the populations (*Note: If the mortality rates of a specific community are compared to the national population, then the national population is considered as a “standard” population). Multiply the agespecific mortality rates of the other population under study to the number of persons in each age group of the standard population. By this way, you will get the expected deaths for each age group of each population. Add the number of expected deaths from all age groups. Finally to get the ageadjusted mortality rates, divide the total number of expected deaths by the standard population. Now you can conclude by comparing the agestandardized mortality rates of two populations 
Choose a reference or standard population. Calculate the observed number of deaths in the population (s) of interest. Apply the agespecific mortality rates from the chosen reference population to the population(s) of interest. Multiply the number of people in each age group of the population(s) of interest by the agespecific mortality rate in the comparable age group of the reference population. Sum the total number of expected deaths for each population of interest. Divide the total number of observed deaths of the population(s) of interest by the expected deaths 


Calculation Rates
Definition 
Calculation 
Incidence rate is the number of new cases of a specified healthrelated state or event reported during a given time interval 
Incidence Rate= New cases occurring during a given time period/population at risk during the same time period multiplied by 10z 
Mortalilty Rate is the total number of deaths reported during a given time 
Mortality Rate = Deaths occurring during a given time period/ Population from which deaths occurred Multiplied by 10z 
PersonTime Rate When the denominator of the incidence rate is the sum of the time each person was observed 
Person Time rate= New cases occurring during an observationperiod/Time each person observed, totaled for all persons multiply by 10z 
Attack Rate It involves a specific population during a limited time period, such as during a disease outbreak. It is also referred to as a cumulative incidence rate or risk 
Attack Rate=New cases occurring during a shirt time period/Population at risk at the beginning of the time period multiplied by 100 
Secondary Attack Rate the rate of new cases occurring among contacts of known cases. 
Secondary Attack Rate= New cases among contacts of primary cases during a short time period/(Populations at beginning of time period) (primary cases) multiplied by 100 
Point Prevalence he frequency of an existing healthrelated state or event during a time period. 
Point Prevalence= Existing cases of a disease or event at a point in time/total study population at a point in time multiplied by 100 

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