Chapter 2: Health Data & Data Distributions Flashcards
2.1 Create frequency distributions of nominal data 2.2 Calculate proportions, percentages, ratios, and rates 2.3 Create simple and grouped frequency distributions 2.4 Use cross-tabulations 2.5 Distinguish between various forms of graphic presentations
How do Public Health researchers use formulas and statistical techniques?
- To organize raw data, and
2. To test hypotheses
How do Public Health researchers use frequency tables?
To make raw data, which is often difficult to synthesize, easier to understand.
What are the characteristics of a frequency distribution of nominal data?
- Title
- Two columns
- Left column: characteristics
- Right column: frequency (f)
What are some ways to summarize categorical/nominal data?
- Frequency distributions (tables)
- Comparisons of frequency distributions (tables)
- Calculations of proportions, percentages, ratios, and rates
Why do researchers synthesize raw data?
In order to observe any patterns which might yield useful hypotheses, which can be tested
Why compare frequency distributions?
To clarify results and add information
What is a proportion?
A comparison of the number of cases to the total size of a distribution
What is the purpose of a proportion or a percentage?
The comparison of groups of different sizes
What is the formula for a proportion?
P = f/N
What is a percentage?
The frequency of occurrence of a category per 100 cases
What is the formula for a percentage?
% = (100) f/N
What is a ratio?
A comparison of the frequency of one category to another
What is the formula for a ratio?
Ratio = f1/f2
What is a rate?
A comparison of actual occurrences to potential occurrences
What is the formula for a rate?
Rate = f actual cases/f potential cases)
How are grouped frequency distributions of interval/ratio data used?
To clarify the presentation of interval-level scores spread over a wide range
What are class intervals?
Smaller categories or groups containing more than one score
How is a class interval frequency determined?
By the number of score values (units of observation) the category contains
What is a class limit?
The midpoint between class intervals
How is the size of a class interval determined?
By calculating the distance between the upper and lower limits of the class interval
What is the midpoint of a class interval?
The middlemost score value in a class interval
Why are midpoints important?
Midpoints are used to represent a class interval when it has to be represented by a single point.
What is a cumulative frequency?
- The total number of cases having a given
score or a score that is lower - Shown as “cf”
How is a cumulative frequency obtained?
By calculating the sum of frequencies in a category plus all the lower categories’ frequencies
What is a cumulative percentage?
- The percentage of cases having a given score or a
score that is lower - Shown as “c%”
What is a percentile?
The percentage of cases falling at or below a certain score
What are deciles?
Points that divide a distribution into 10 equal portions
What are quartiles?
Points that divide a distribution into quarters
What is a median?
The point that divides a distribution in two, half above it and half below it
Name 5 forms of graphic representation of data
- Pie charts
- Bar charts - Nominal and ordinal data
- Histograms
- Frequency polygons (line charts)
- Maps
What is the formula for calculating the midpoint of a class interval?
m = lowest score value + highest score value/2
What is the formula for calculating cumulative percentage?
c% = (100) cf/N
What is the formula for calculating the size of a class interval?
i = U - L
