Lesson 4 Epidemiology

semilogarithmic-scale line graphs

-The slope of the line indicates the rate of increase or decrease. • A straight line indicates a constant rate (not amount) of increase or decrease in the values. • A horizontal line indicates no change. • Two or more lines following parallel paths show identical rates of change.

B.

A 100% component bar chart shows the same data as a stacked bar chart. The key difference is in the units on the x-axis. A. True B. False

A.

A constant rate of change would be represented by a curved line A. Arithmetic-scale line graph B. Semilogarithmic-scale line graph C. Both D. Neither

A, C

A scatter diagram is the graph of choice for plotting: A. Anabolic steroid levels measured in both blood and urine among a group of athletes B. Mean cholesterol levels over time in a population C. Infant mortality rates by mean annual income among different countries D. Systolic blood pressure by eye color (brown, blue, green, other) measured in each person

B.

A spot map must reflect numbers; an area map must reflect rates. A. True B. False

A, B, C, D

A table in a report or manuscript should include: A. Title B. Row and column labels C. Footnotes that explain abbreviations, symbols, exclusions D. Source of the data E. Explanation of the key findings

contingency table

A two-variable table with data categorized jointly by those two variables

B.

In an oral presentation, three-dimensional pie charts and three-dimensional columns in bar charts are desirable because they add visual interest to a slide. A. True B. False

A

Number of cases of dog bites by age group (adult or child) and sex of the victim A. Grouped bar chart B. Histogram C. Line graph D. Pie chart

D

Number of cases of dog bites by breed of the dog A. Grouped bar chart B. Histogram C. Line graph D. Pie chart

C, B

Number of cases of dog bites over time A. Grouped bar chart B. Histogram C. Line graph D. Pie chart

C

Number of cases of dog bites per 100,000 population over time A. Grouped bar chart B. Histogram C. Line graph D. Pie chart

B, C

On an arithmetic-scale line graph, the x-axis and y-axis each should: A. Begin at zero on each axis B. Have labels for the tick marks and each axis C. Use equal distances along the axis to represent equal quantities (although the quantities measured on each axis may differ) D. Use the same tick mark spacing on the two axes

B.

Reasonable categories for a disease that mostly affects children under age 5 years are: Age Group <1 year 1-2 3-4 4-5 >5 a. True b. False

A, B, C, D, E

Recommended methods for creating categories for continuous variables include: A. Basing the categories on the mean and standard deviation B. Dividing the data into categories with similar numbers of observations in each C. Dividing the range into equal class intervals D. Using categories that have been used in national surveillance summary reports E. Using the same categories as your population data are grouped

B, C, D

Tables and graphs are important tools for which tasks of an epidemiologist? A. Data collection B. Data summarization(descriptiveepidemiology) C. Data analysis D. Data presentation

B.

The y-axis tick labels could be 0.1, 1, 10, and 100 A. Arithmetic-scale line graph B. Semilogarithmic-scale line graph C. Both D. Neither

B.

To display different rates on an area map using different colors, select different colors that have the same intensity, so as not to bias the audience. A. True B. False

Histogram

What kind of graph is an epidemic curve?

D.

Which of the following requires more than one variable? A. Frequency distribution B. One-variabletable C. Pie chart D. Scatter diagram E. Simple bar chart

C.

Which of the following shapes of a population pyramid is most consistent with a young population? A. Tall, narrow rectangle B. Short,wide rectangle C. Triangle base down D. Triangle base up

chance node

a circle, with branches representing different outcomes that occur by chance, one and only one of which occurs.

decision node

a square, with branches representing the choices in the decision-tree diagram

phylogenic tree

a type of dendrogram, is a branching chart that indicates the evolutionary lineage or genetic relatedness of organisms involved in outbreaks of illness. Distance on the tree reflects genetic differences, so organisms that are close to one another on the tree are more related than organisms that are further apart.

100% component bar chart

a variant of a stacked bar chart, in which all of the bars are pulled to the same height (100%) and show the components as percentages of the total rather than as actual values. This type of chart is useful for comparing the contribution of different subgroups within the categories of the main variable.

forest plot

also called a confidence interval plot, is used to display the point estimates and confidence intervals of individual studies assembled for a meta-analysis or systematic review

continuous variables

can have any value in a range (e.g., amount of time between meal being served and onset of gastro-intestinal symptoms; infant mortality rate).

deviation bar chart

chart displays both positive and negative changes from a baseline.

graph

displays numeric data in visual form. It can display patterns, trends, aberrations, similarities, and differences in the data that may not be evident in tables.

population pyramid

displays the count or percentage of a population by age and sex. It does so by using two histograms — most often one for females and one for males, each by age group — turned sideways so the bars are horizontal, and placed base to base

histogram

graph of the frequency distribution of a continuous variable, based on class intervals. It uses adjoining columns to represent the number of observations for each class interval in the distribution. The area of each column is proportional to the number of observations in that interval.

ordinal variables

have an intrinsic order, but, again, differences between levels are not relevant.

discrete variables

have values that are integers (e.g., number of ill persons who were exposed to a risk factor).

epidemic curve

histogram that displays the number of cases of disease during an outbreak or epidemic by times of onset. The y-axis represents the number of cases; the x- axis represents date and/or time of onset of illness.

scatter diagram

is a graph that portrays the relationship between two continuous variables, with the x-axis representing one variable and the y-axis representing the other.

frequency polygon

is the graph of a frequency distribution; the number of observations within an interval is marked with a single point placed at the midpoint of the interval. Each point is then connected to the next with a straight line.

cycle

order of magnitude

cumulative frequency curve

plots the cumulative frequency rather than the actual frequency distribution of a variable. This type of graph is useful for identifying medians, quartiles, and other percentiles. The x-axis records the class intervals, while the y-axis shows the cumulative frequency either on an absolute scale

tables

set of data arranged in rows or columns

arithmetic-scale line graph

shows patterns or trends over some variable, often time. In epidemiology, this type of graph is used to show long series of data and to compare several series. It is the method of choice for plotting rates over time.

pie chart

simple, easily understood chart in which the size of the "slices" or wedges shows the proportional contribution of each component part

decision analysis

systematic method for making decisions when outcomes are uncertain.

Semilogarithmic-scale line graphs

this technique is useful for displaying a variable with a wide range of values. The x- axis uses the usual arithmetic-scale, but the y-axis is measured on a logarithmic rather than an arithmetic scale. As a result, the distance from 1 to 10 on the y- axis is the same as the distance from 10 to 100 or 100 to 1,000.

grouped bar chart

used to illustrate data from two-variable or three-variable tables.;useful when you want to compare the subgroups within a group.

maps

used to show the geographic location of events or attributes.

stacked bar chart

used to show the same data as a grouped bar chart but stacks the subgroups of the second variable into a single bar of the first variable. It deviates from the grouped bar chart in that the different groups are differentiated not with separate bars, but with different segments within a single bar for each category.

tables

useful for demonstrating patterns, exceptions, differences, and other relationships.

bar chart

uses bars of equal width to display comparative data. Comparison of categories is based on the fact that the length of the bar is proportional to the frequency of the event in that category.

dot plot

uses dots to show the relationship between a categorical variable on the x-axis and a continuous variable on the y-axis. A dot is positioned at the appropriate place for each observation.