SAC360

1. Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com.
CHAPTER 7
Statistics:
Making Sense
of Uncertainty

2. Copyright
©
2021
by
Jones
&
Bartlett
Learning,
LLC
an
Ascend
Learning
Company.
www.jblearning.com
Statistics
 Is a set of concepts and methods used to analyze data in order to extract
information
 Is the science used to interpret the numbers that describe the health of the
population
 Makes possible the translation of data into information about causes and
effects, health risks, and cures of diseases

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©
2021
by
Jones
&
Bartlett
Learning,
LLC
an
Ascend
Learning
Company.
www.jblearning.com
The Uncertainty of Science
 Most science is of a probable nature.
 In many cases, there is not enough data to give us a degree of certainty, or the
existing data is too ambiguous to allow a valid conclusion.
 Science is ongoing; studies may contradict each other.
 The science of statistics can quantify the degree of uncertainty.

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©
2021
by
Jones
&
Bartlett
Learning,
LLC
an
Ascend
Learning
Company.
www.jblearning.com
Probability
 The probable is what usually happens.
 Probabilities are used to describe the variety and frequency of past outcomes
under similar conditions as a way of predicting what should happen in the
future.
 A p-value:
– When p ≤ 0.05, it usually means that a result is statistically significant.
– When p = 0.05, there is still a 5% chance that the result is wrong.
 Key concepts are:
– Confidence interval
– Law of Small Probabilities

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©
2021
by
Jones
&
Bartlett
Learning,
LLC
an
Ascend
Learning
Company.
www.jblearning.com
Power of a Study
 There is the probability of finding an effect if there is, in fact, an effect.
 Large numbers confer power.
 Studies with low power are likely to produce false-negative results.

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©
2021
by
Jones
&
Bartlett
Learning,
LLC
an
Ascend
Learning
Company.
www.jblearning.com
Statistics of Screening Tests
 Examples of screening:
– Mammography for breast cancer
– HIV tests
– Newborn screening
 Sensitivity versus specificity
 False positives versus false negatives
 Lead-time bias
 Overdiagnosis bias

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©
2021
by
Jones
&
Bartlett
Learning,
LLC
an
Ascend
Learning
Company.
www.jblearning.com
Rates
 Rates relate raw numbers to the size of the population being considered.
– Birth rates
– Mortality rates
 Other rates commonly used as indicators of community health are:
– Infant mortality rate
– Maternal mortality rate
 Crude rates
 Adjusted rates
– Age adjusted
 Group specific rates
– Gender specific

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©
2021
by
Jones
&
Bartlett
Learning,
LLC
an
Ascend
Learning
Company.
www.jblearning.com
Other Calculated Statistics
 Life expectancy
 Years of potential life lost (YPLL)

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©
2021
by
Jones
&
Bartlett
Learning,
LLC
an
Ascend
Learning
Company.
www.jblearning.com
Risk Assessment and Risk Perception
 Risk assessment:
– Identifies events and exposures that may be harmful to humans
– Estimates the probabilities of their occurrence
– Estimates the extent of harm they may cause
– For well-known risks, we can calculate from historical data.
– For poorly understood risks, we must make many assumptions.
 Risk perception:
– Involves psychological factors
– Is the result of the apparent irrationality of the public in response to risks that
experts estimate to be small
– Is classified on two scales: dread and knowability

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©
2021
by
Jones
&
Bartlett
Learning,
LLC
an
Ascend
Learning
Company.
www.jblearning.com
Cost–Benefit Analysis
 Weighs the estimated cost of implementing a policy against the estimated
benefit, usually in monetary terms
 Costs are easier to calculate than benefits.
 What monetary value can we put on a life saved?
 Analysis is often controversial.
 Cost-effectiveness analysis compares the efficiency of different methods of
attaining the same objective.

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©
2021
by
Jones
&
Bartlett
Learning,
LLC
an
Ascend
Learning
Company.
www.jblearning.com
Discussion Question 1
 Why is statistics so important for public health?

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©
2021
by
Jones
&
Bartlett
Learning,
LLC
an
Ascend
Learning
Company.
www.jblearning.com
Discussion Question 2
 Try organizing a group of students in a
coin-tossing experiment.
 How often does the same side come up five times in a row?
 Ten times in a row?

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Jones
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Bartlett
Learning,
LLC
an
Ascend
Learning
Company.
www.jblearning.com
Discussion Question 3
 Think of a medical test that you or someone you know has undergone.
 Was it more important for the test to be sensitive or for it to be specific? Why?
 What would be the implications if the result was a false positive?
 What if there had been a false-negative result?

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©
2021
by
Jones
&
Bartlett
Learning,
LLC
an
Ascend
Learning
Company.
www.jblearning.com
Discussion Question 4
 Consider the list of activities and technologies presented in Table 7-4.
 Rank them in order of your willingness to accept the risk.
 How does your ranking compare with those of the other groups shown in the
table?

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©
2021
by
Jones
&
Bartlett
Learning,
LLC
an
Ascend
Learning
Company.
www.jblearning.com
Discussion Question 5
 Visit Rice Virtual Lab in Statistics by statistician David Lane,
onlinestatbook.com/rvls.html.
 Choose one of Lane’s case studies that is relevant to health and describe the
experimental design.
 What are the conclusions of the experiment?
 Are the results significant?
 Is a p-value given?