Multiple ways to classify Data
Types of data |
Nominal Data: unordered categories.
Dichotomous is nominal data that have two distinct values
Ordinal Data: information provided by the order among categories. Common in health behavior research
Discrete Data: intergers or counts that differ by fixed amounts, with no intermediate values possible
Continous Data: measurable quantities not restricted to taking on integer values.
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Measuremnts of Data
Give an example of ratio?
1 in 6 unintentional deaths are suicides. |
How is proportion normally expressed?
As a percentage |
Give an example of proportion
123 people were infected, 44 died. Proportion: 44/123= 0.36 or 36% |
What is Rate?
A Frequency measure that involves nominal data |
What is attack rate ?
New cases that start to occur rapidly overtime in a defined population |
What is Person-Time rate also known as?
Incidence Density Rate |
What is the difference between mortality rate and incidence rate ?
Mortality rate is deaths occurring during a given time period. Incidence rate is New cases occurring during a given time period |
What is the formula for SAR ?
(new cases among contacts of known cases)/█((population at beginning of time period)-(primary cases)(*100) |
What is SAR?
Secondary Attack Rate: New rate of cases occurring among known cases |
What is point prevalence?
Existing cases of a disease at a point in time |
Other forms of Measurements cont'd
Numerical Methods |
Measures of dispersion |
Arithmetic Mean, geometric mean, Median, Mode |
Range, Interquartile range, Variance, Standard deviation, coefficient of variation |
Measures of Association
When measuring the association between two nominal or ordinal variables data is entered into a contingency table |
When using a contingency table all entries are classified by each variable in the table. |
Interquartile Data + Box Plot example.
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Age Adjusted Rates
Crude Rate: An outcome Calculated without any restriction (i.e gender or age). Crude rates can be calculated for entire populations or in a subgroup
Example: Crude Rate of Motor Vehicle Traffic Fatalities in California, Years 2008–2014
Total Motor Vehicle Traffic Deaths in California from 2008 through 2014 = 21,854
Total Population in California from 2008 through 2014 (summed across years) = 263,818,096 Crude Rate = (21,854 ÷ 263,818,096) × 100,000 = 8.28 per 100,000 population |
Age- adjusted rate: Summary measures adjusted for differences in age distributions
Age-adjusted rates may be preferred for injuries that occur more often among certain age groups than others.
Example: "fall-related deaths are more common among the elderly than any other age group." |
Direct Method = deaths in age group ÷ estimated population of that age group × 100,000.
a given areas age-specific rate |
Indirect Method: a common set of age-specific rates is applied to the populations whose rates are to be standardized. |
Standard Morbidity/Mortality Rate Ratio= SMR
Used less frequently than direct method. SMR=Observed/Expected.
useful when age-specific numbers of deaths in the study population are either unavailable or small in number (less than 25 events across all age groups, as per Curtin & Klein, 1995). |
Other Forms of Measuremnts used in Public Health
Frequency Distribution: complete summary of the frequencies, or number of times each value appears. |
Other ways to measure data: Bar Charts, steam and leaf plots, box plot, two way scatter plot, line graph, a spot map or area map. |
Relative Frequency: dividing the number of people in each group by total number of people.
May normally used for presenting the frequency of nominal, ordinal, discrete, or continuous data. |
A histogram shows distribution for discrete or continous data
An epidemic curve is a histogram that shows the course of an epidemic by plotting number of cases X time of onset |
Excerpt From Introduction to Epidemiology Ray M. Merrill;
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