Statistical Table & Statistical Graph

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Statistical Table &amp; Statistical Graph. Zhang Guozhen School of Public Health Xinjiang Medical University. Statistical Tables and Graphs. Statistical description is a kind of fundamental work for statistical inference, which describes the feature of the sample.

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Statistical Table & StatisticalGraph

Zhang Guozhen

School of Public Health

Xinjiang Medical University

Statistical Tables and Graphs
• Statistical description is a kind of fundamental work for statistical inference, which describes the feature of the sample.
• The main forms for description are tables, graphs and numerical indexes.
• Statistical tables and graphs are two kinds of forms made of point, line, area and number.
• They can show the information of data directly. So they are widely used in medical practice.
Statistical Tables

Example1 125 children were tested in county B and 9 cases were found In this study, 221 children were tested in county A and 4 cases were found suffering from rachitis; the prevalence rate was 18.10 per thousand.; the prevalence rate was 72.00 per thousand. 248 children were tested in county C and 2 cases were found; the prevalence rate was 8.00 per thousand…..

• Very tired and verbose.
• Difficult to remain any impression
Put into a table

Table 1 Rachiotis prevalence rates in 5 counties

• Clearimpression !
• Easy to compare each other !
Principles of Making Tables
• Primary and secondary contents as well as arrangement must be clear
Construction of Statistical Table
• Title:generalize the contents, including time and site. The title is located on the top of the table and a sequence No. is on the left of the title.
• Horizontal item:indicate the subjects investigated, usually located in the left of the table.
• Vertical item:indicate statistical index including the units, usually located in the right and upper of the table.
Lines (horizontal only):
• Top and bottom (dark): define the range of table
• Others (light): separate items and figures.
• Not suitable to having too many lines. The vertical lines and skew lines can’t be allowed.
• Figures:require to use Arabian number in the statistical table and the decimal must be accordant. The empty cells can’t be allowed.
• Notes:usually use star mark “  ” to express notes,

and the mark “  ” usually put on the bottom of

the table.

Basic Structure of Statistical Table

Table 1 Table title

Top line

Item line

Total line

Bottom line

Types of Statistical tables
• Simple table:One variable only
• Combinative table: More than 2 variables
Simple Table
• Row item: Subject
• Column item: Predicate
• The group of HBsAg carriers has 1457 persons tested, among which 46 positive with positive rate 3.16%.
• 2. The group of HB patients has 1224 persons tested, among which 161 positive with positive rate 13.15%.
Table 4 the result of HBsAg of persons at different age group in city or country at certain area in certain year
Announcements of Making Statistical Table

Example 2

The mental score and other factors related to coronary heart disease were researched in certain area. The results were shown in table 5

Problems in above Table
• Too much content was put in a table, especially, the measurement data and numeration data were put in a table.
• Many blank space in table because of incompatible content in different column.
• Inversion of row item and column item
• Too much content, complex ranks, data inappropriately arranged in table
Table 6 compare of the risk factor of patients with coronary heart disease (X±S)

Solution：dividing it into two tables, table 6,7

Frequent Mistakes in Tables
• Title: Not exactly fit the content
• Content:

Too much;

Mix of important and many non-important ones

• Items:Inappropriately arranged
• Figures:

Total and subtotals; Digits and decimals

• Lines: Using vertical lines and oblique lines
Statistical Graphs
• advantage: data visualization and remaining impression.
• The purpose of using graphic displays is to give a quick overall impression of the data, which is sometimes difficult to obtain with numeric measures.

bar graph, histogram, percent bar chart,

pie chart, line graph, scatter plot ,statistical map, stem-leaf plot, box plot, residual plot

Basic requirements:
• Axis: Y-axis (vertical) and X-axis (horizontal).
• Legend:explain meaning of colors or patterns.
• Title:under the graph; content, time, place.
Principle
• Select the proper graph according to different aim of study and the character or feature of data.

below the graph

Index and unit are shown in the Y-axis and X-axis. The point of intersection commonly is 0. The ratio of Y-axis to X-axis is 5：7 properly.
• Different lines and colors indicate different statistical value of subjects. Marginal data is attached to the graph.
• Legends are the notes of a statistical graph, usually located on the right top corner or located between the bottom of the graph and the title.
Basic Structure of a Statistical Graph

legend

Vertical item (unit)

legend

Graph body

0

Horizontal item (unit)

Fig 1 The basic structure of a statistical graph

Content
• bar chart
• pie chart
• percent bar chart
• line graph
• Histogram
• Scatter Diagram
Bar Chart
• Compare figures of different populations
• Display the comparison among similar and relative independent data
• Often used to compare the level of the variable at several locations
• simple bar chart or complex bar chart

Bar chart is selected because the cause of death is interdependent indexes. Simple bar chart , only classified by the cause of death .

Fig.3 Average cost of outpatients for several treatments in a hospital in 1994 and 1997
Guidelines for Bar Charts
• Label both axes clearly
• Leave space between bars
• Leave space between the left-most bar and the vertical axis
• When possible, begin the vertical axis at 0
• All bars should be the same width
Pie Chart
• Describe percentages of all the parts of population
• Indicate the proportion
• The 360o angle at the centre is apportioned to each item in the total in proportion of its magnitude .
Guidelines for Pie Charts:
• Give clear, complete title
• Label all sections clearly
• use a legend or key
• Order by frequency
• Start at top (12:00)
• Move clockwise from start

10%

40%

15%

17%

18%

Fig.5 Percentages of the reasons for re-addiction (xx place,1996)

Percent Bar Chart

Compare frequencies of a category variable

• Indicate the proportion

Fig. 6 Mother’s education manner in group of drug addicts and group of controls. (xx place, 1996)

Line Graph

Describe the changing of Y with X (time) -- tendency

Fig. 7 Incidence rates of stomach cancer in a city

General Line Graph
• Used for expressing a phenomenon changes with the time and condition, or one phenomenon changes with another phenomenon.
• Its horizontal axis and vertical axis are all arithmetic rules.
Semi-logarithmic Line Graph
• Used for expressing the developing velocity (relative number) of a phenomenon changes with the time ,condition, or another phenomenon.
• Unlike a general line graph, its horizontal axis is arithmetic rule and vertical axis is logarithmic rule.
Semi-logarithmic Line Graph

Left: The absolute difference of mortality rates ~ Year

Right: The absolute difference of log (mortality rate)

Suitable line graphs in different situation

Histogram
• Describe a frequency distribution of continuous Quantitative Data
• A histogram is a diagram in which:
• The horizontal scale represents the value of the variable marked at interval boundaries.
• The vertical scale represents the frequency or relative frequency in each interval
• It is a picture of the number of observations in each of the class intervals
• The bars are adjacent or touching, which reflects the continuity of the data
• Equal width intervals are strongly recommended
• Area (width x height) of bar represents proportion

in the interval

Some guidelines for constructing histograms :
• The graph title should be a complete description of the graph
• Clearly label both the horizontal and vertical axes
• label either endpoints or midpoints on horizontal axis
• Include all intervals, even when “empty”
• Break axes when necessary
• Use equal class widths
Scatter Diagram

Describe the relationship between two numerical variables.

Is the relationship linear or non-linear?

Summary
• A nice table can save a lot of words, show the fundamental characteristics and their relationship clearly.
• Comparing to statistical tables, nice looking statistical plots are even more intuitive and understandable.
• Contrarily, a poor organized table or a messy plot may sicken people.