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Descriptive Statistics
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Descriptive Descriptive StatisticsStatisticsMahdi AkbarzadehMahdi AkbarzadehDepartment of Biostatistics and Department of Biostatistics and
EpidemiologyEpidemiology
Statistics
Two areas of statistics:
Generally the field of statistics can be divided in two parts:
Descriptive
Inferential
Descriptive Statistics
Descriptive Statistics are Used by Researchers to Report on Populations and Samples
In Medical Research: Summary descriptions of measurements (variables)
taken about a group of people
By Summarizing Information, Descriptive Statistics Speed Up and Simplify Comprehension of a Group’s Characteristics
An Illustration:
Which Group is Smarter?
Class A--IQs of 13 Students
102 115
128 109131 8998 106
140 119
93 97110
Class B--IQs of 13 Students
127 162131 10396 11180 109 93 87120 105109
Each individual may be different. If you try to understand a group by remembering the qualities of each member, you become overwhelmed and fail to understand the group.
Which group is smarter now?
Class A--Average IQ Class B--Average IQ
110.54 110.23
They’re roughly the same!
With a summary descriptive statistic, it is much easier to answer our question.
Methods for Descriptive Statistics
One Variable Descriptions :o Describing VRs with tablestables and graphsgraphso Numerical descriptions with StatisticsStatistics
Bivariate Descriptions: o Combining above methods: Two way tables, Clustered Bar
charts, . . .
- In practice, most studies have several VRs
Describing by Tables and GraphsTables and Graphs
Qualitative or Categorical VRs (Sex, Age group, Oral hygiene level, . . . )
- Frequency Table (One-way)- Bar Charts- Pie Charts
Quantitative or Continuous VRs (Age, Time, Number of teeth, . . . )
- Histogram- Box plot- Categorize
Describing by Tables and GraphsTables and Graphs
Qualitative or Categorical VRs (Sex, Age group, Oral hygiene level, . . . )
- Frequency Table (One-way)
Describing by Tables and GraphsTables and Graphs
Qualitative or Categorical VRs (Sex, Age group, Oral hygiene level, . . . )
- Bar Charts
Describing by Tables and GraphsTables and Graphs
Quantitative or Categorical VRs (Sex, Age group, Oral hygiene level, . . . )
- Pie Charts
Describing by Tables and GraphsTables and Graphs
Quantitative or Continuous VRs (Age, Time, Number of teeth, . . . )
- Histogram
Describing by Tables and GraphsTables and Graphs
Quantitative or Continuous VRs (Age, Time, Number of teeth, . . . )
- Box plot
Describing by StatisticsStatistics
Types of Statistics:- Central Tendency- Percentile Values- Dispersion- Distribution
Histogram of age
age
Frequency
16 18 20 22 24
050000
100000
150000
Symmetrical Distribution
Unsymmetrical Distribution (Skewed)
Tall and Short Distribution (Kurtosis)
