Download Lecture 11 - What Are We Summarizing

What Are We
Summarizing?
Lecture 11
Sections 4.1 – 4.2
Tue, Feb 1, 2005
What Are We Summarizing?
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There are various types of data.
How the data are summarized depends on the
type of data.
See Data Set 1, p. 184.
How best to summarize Gender?
 How best to summarize Age?
 How best to summarize Blood Pressure?
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Qualitative Variables
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Qualitative variable – A variable whose values
are not numerical, but can be divided into
categories.
The values of a qualitative variable may or may
not have a natural order.
Examples:
Gender.
 Questionnaire response, from strongly agree to
strongly disagree.
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Quantitative Variables
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Quantitative variable – A variable whose values
are numerical.
A quantitative variable may be continuous or
discrete.
Continuous Variables
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Continuous variable – The set of theoretically
possible values of the variable forms a continuous
set of real numbers.
Typically these are measured quantities: length,
time, area, weight, etc.
Example: The length of time a student takes to
complete a test.
Usually modified by “much,” not “many.”
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How much time will it take?
Discrete Variables
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Discrete variable – The set of theoretically
possible values of the variable forms a set of
isolated points on the number line.
Typically this is count data; a verbal description
usually contains the phrase “the number of.”
Example: The number of students who
completed the test within 40 minutes.
Usually modified by “many,” not “much.”
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How many students finishes the test?
Discrete vs. Continuous
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Some data may be considered to be either
discrete or continuous.
Example: Time.
How much time do I have for the test?
 How many minutes do I have for the test?
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Example: Money.
How much money is in your pocket?
 How many dollars are in your pocket?
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In such cases, consider it to be continuous.
Discrete vs. Continuous
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Some data may be considered to be either
discrete or continuous.
Example: Time.
How much time do I have for the test?
 How many minutes do I have for the test?
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Example: Money.
How much money is in your pocket?
 How many dollars are in your pocket?
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In such cases, consider it to be continuous.
Discrete vs. Continuous
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The distinction is based on the nature of the
variable, not the manner in which it is measured
or recorded.
Example: Measure the time it takes each student
to finish a test, to the nearest minute.
The possible times are 0, 1, 2, 3, … minutes.
 Is that discrete or continuous?
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Let’s Do It!
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Think about it, p. 188.
Let’s do it! 4.1, p. 187 – What Type of Variable?
Example
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Revisit the study one more time.
The Role of Cyclooxygenase-2 Inhibitors in
Fusion Rates of Hindfoot Arthrodesis
What kind of data were collected?
 How were these data summarized?
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COX-2 Study
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The group that received the COX-2 inhibitor
medication had an overall nonunion rate of
11.2%.
For all patients that achieved arthrodesis,
average time to union was 89.8 days for this
group.
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When separated by arthrodesis site, the majority of
nonunions were failed ankle arthrodesis (96%).
COX-2 Study
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In the group that did not receive a COX-2
inhibitor postoperatively, the overall nonunion
rate was 12.4%,
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again with failed ankle arthrodesis accounting for the
majority of the nonunions (97%).
Time to union in this group averaged 93.4 days.
COX-2 Study
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The time to union was shorter in the group that
received COX-2 inhibitors, but this was not
statistically significant.
The overall nonunion rate was lower in the
group that received COX-2 inhibitors, but this,
too, was not statistically significant.