Statistics: Bell Curve Concepts

Questions and Answers

Identify the median in the following list of numbers: 6, 2, 9, 7, 1, 4.

5 (correct)

In a study whether Operating room A (OR A) is associated with a higher number of surgical site infections (SSIs) than Operating room B (OR B), the infection preventionist (IP) concludes that the SSI rate in OR A is not equal to the SSI rate in OR B, but in reality, the two rates are equal. What type of statistical error has she committed?

She committed a Type II error

No error has been committed

She committed an error equal to β

She committed a Type I error (correct)

For which of the following procedure(s) is the surveillance period for deep incisional or organ/space SSI 90 days?

1, 4

1, 2

2, 3 (correct)

3, 4

An appropriate indicator to monitor process compliance would be:

Appropriate antibiotic dosage Signup and view all the answers

What key infection control activity is defined as the systematic, ongoing collection, management, analysis, and interpretation of data followed by the dissemination of these data to public health programs?

Surveillance Signup and view all the answers

An IP is reading a journal article that states the data the authors collected are normally distributed. What does this mean?

The mean, median, and mode of the data are equal Signup and view all the answers

Which of the following is indicative of a superficial SSI?

Pain at the incision site 10 days after a breast reduction procedure; drainage is culture positive for methicillin-susceptible Staphylococcus aureus (MSSA) Signup and view all the answers

What information will be needed to calculate a CLABSI rate for the ICU?

3, 4 Signup and view all the answers

What type of rate would the IP want to calculate to give feedback to the surgeons at her facility?

Provider-specific Signup and view all the answers

The chi-square test can be used:

If each cell of the table is greater than 5 Signup and view all the answers

The measure of central tendency most affected by outliers is:

Mean Signup and view all the answers

In any normal distribution, the proportion of observations that are within two standard deviations of the mean is closest to:

0.95 Signup and view all the answers

The most important feature of nonparametric tests is that they:

Make no assumption about variance in the populations Signup and view all the answers

Which of the following indicates a strong positive correlation?

r = 0.603 Signup and view all the answers

Which of the following groups is the most appropriate control in a case-control study for infections associated with a health club?

Non-ill members of the health club matched for age and sex Signup and view all the answers

Which of the following steps are not included in hypothesis testing?

Eliminate outliers Signup and view all the answers

The range of the correlation coefficient is:

-1 to 1 Signup and view all the answers

If the index of kurtosis is -1.99, then the curve is:

Relatively flat Signup and view all the answers

The probability or likelihood of an event occurring is the:

Risk Signup and view all the answers

A table is used to illustrate data:

Arranged in rows and columns Signup and view all the answers

Calculate the mode for the following set of numbers: 2, 11, 5, 21, 3, 11, 8, 26

11 Signup and view all the answers

As the sample size increases, how is the power of the study affected?

Power is increased Signup and view all the answers

The term for an extraneous variable that systematically varies with the independent variable and influences the dependent variable is a:

Confounding variable Signup and view all the answers

When a normal distribution is graphed, which of the following are true?

1, 2, 4 Signup and view all the answers

Which of the following is not considered one of the criteria for causality?

The association has been observed in numerous studies Signup and view all the answers

Which of the following are true about a frequency polygon?

1, 3 Signup and view all the answers

Targeted surveillance focuses on:

Tracking high-risk, high-volume procedures and potentially preventable healthcare-associated infections (HAIs) Signup and view all the answers

The number of hand hygiene episodes performed by personnel divided by the number of patient days times 1,000 is a key indicator to assess:

Adherence to hand hygiene policies Signup and view all the answers

Which of the following viruses is the causative agent in Kaposi's sarcoma?

Human herpesvirus 8 Signup and view all the answers

Which of the following is true regarding the epidemiology of coccidioidomycosis?

Up to 50 percent of people in endemic areas have been exposed to Coccidioides spores Signup and view all the answers

The proportion of a disease that could be prevented by eliminating the exposure in the entire study population can be determined by calculating the:

Population attributable risk percent Signup and view all the answers

The precision of an estimate of a relative risk depends on which of the following?

Size of the study Signup and view all the answers

The most common reservoir for highly pathogenic avian influenza H5N1 virus is:

Domestic poultry Signup and view all the answers

Which of the following is the term for the interrelation of indirect and direct causes of disease?

Causal web Signup and view all the answers

Which of the following statements is true when the prevalence of a disease is very low?

The positive predictive value of a diagnostic test is lowered Signup and view all the answers

Which of the following statements regarding the epidemiology of norovirus infection supports this scenario?

Noroviruses are the most common cause of epidemic gastroenteritis worldwide Signup and view all the answers

What is the attributable risk between the exposed and unexposed population in the table?

0.56 Signup and view all the answers

Which of the following statements is most accurate regarding the relationship between IBD and CDI?

IBD is associated with increased morbidity and mortality associated with CDI Signup and view all the answers

Which of the following statements about TB and airborne diseases among homeless individuals is most accurate?

Most TB infections among homeless individuals are reactivations of established disease Signup and view all the answers

Which of the following odds ratios is correct in a case-control study examining obesity and Clostridium difficile?

2.85 Signup and view all the answers

Study Notes

Surveillance and Epidemiologic Investigation Key Concepts

Median Calculation: The median is the middle value of an ordered data set. For the numbers 6, 2, 9, 7, 1, 4, the ordered set is 1, 2, 4, 6, 7, 9; the median is (4+6)/2 = 5.
Statistical Errors: A Type I error occurs when the null hypothesis is wrongly rejected, implying a false positive. In the context of surgical site infections (SSIs), if OR A is concluded to have a different SSI rate than OR B when they are actually equal, this is a Type I error.
SSI Surveillance Period: According to CDC guidelines, the surveillance period for deep incisional or organ-space SSIs is 90 days for procedures like craniotomy and coronary artery bypass graft.

Monitoring Compliance and Indicators

Process Compliance Indicators: An appropriate indicator for process compliance monitoring is the appropriate antibiotic dosage, which assesses the steps leading to patient outcomes.
Definition of Surveillance: Surveillance refers to the systematic collection, analysis, and dissemination of health data to improve public health actions.

Statistical Understanding

Normal Distribution: In a normally distributed data set, the mean, median, and mode are equal. This results in a bell-shaped curve.
Superficial SSI Criteria: A superficial SSI is identified by symptoms like pain at the incision site and purulent drainage within 30 days post-surgery.
Calculating CLABSI Rate: To calculate a central line-associated bloodstream infection (CLABSI) rate, one needs the number of identified bloodstream infections and the total device days.

Statistical Tests and Measures

Chi-Square Test: This test is used to evaluate the association between two categorical variables and requires that each cell in the contingency table has a count greater than 5.
Influence of Outliers: The mean is significantly affected by outliers, making it less reliable than other measures of central tendency (median and mode).
P-Value Significance: The p-value indicates the probability of committing a Type I error in statistical conclusions.

Epidemiology Concepts

Incidence Density Calculation: The incidence density of MRSA infections is calculated by determining the number of infections occurring in relation to patient days in the surgical service.
Endemic Definition: Endemic refers to an expected number of disease cases in a specific geographic area over time.
Pandemic vs Epidemic: A pandemic is characterized by its spread across multiple countries or continents, unlike an epidemic that may be restricted to a specific area.

Test Specificity and Data Variability

Specificity Calculation: The specificity of a test is calculated as the number of true negatives divided by the total number of persons without the disease.
Measure of Dispersion: The standard deviation and variance measure the dispersion of data around the mean, indicating variability.

Correlation and Hypothesis Testing

Correlation Coefficient Range: The correlation coefficient (r) ranges from -1 to 1, indicating the strength and direction of a relationship between two variables.
Hypothesis Testing Steps: Important steps include stating the null and alternative hypotheses, setting significance levels, and comparing probability values, with outlier elimination not being necessary.

Practical Epidemiology

Control Group in Case-Control Studies: The most suitable control group for a case-control study on infections might be non-ill health club members matched for age and sex.
Statistical Process Control (SPC) Utilization: SPC charts are used for monitoring processes, identifying variation, and tracking outcomes, but not for eliminating natural variation.### Probability and Risk
Probability of an event is often referred to as Risk.
Other related terms include Attack rate, Host factor, and Incidence.

Data Reporting

Study results should be documented in a report.
Effective presentation tools include charts or tables.
Data tables are arranged in rows and columns for clarity.

Statistical Mode

The mode for the numbers 2, 11, 5, 21, 3, 11, 8, 26 is 11.

Sample Size and Study Power

As sample size increases, the power of the study is also increased.

Confounding Variables

An extraneous variable that systematically varies with the independent variable is known as a Confounding variable.

Normal Distribution

A normal distribution has a continuous, symmetrical curve with both tails extending to infinity.
The mean, median, and mode are identical.
Approximately 68.3% of the area lies between the mean and ±2 standard deviations.
Curve shape is defined by mean and standard deviation.

Causality Criteria

For an association to imply causality:
- Higher disease incidence in exposed individuals.
- Established relationship between independent and dependent variables.
- Observations of the association across multiple studies.
- The onset of disease must precede exposure.

Frequency Polygon

A frequency polygon is useful for displaying two sets of data on one graph.
It employs connecting lines and data points and does not use bars on the x-axis.

Targeted Surveillance

Focuses on tracking high-risk, high-volume procedures and potentially preventable healthcare-associated infections (HAIs).

Hand Hygiene Reporting

Hand hygiene adherence can be reported as the number of episodes performed by personnel divided by the number of hand hygiene opportunities by ward or service.

Kaposi's Sarcoma

The causative agent for Kaposi's sarcoma is Human herpesvirus 8.

Coccidioidomycosis Epidemiology

Coccidioides spp. are found on the soil surface and are not typically located at high elevations or found in wet climates.
Up to 50% of individuals in endemic areas may have been exposed to Coccidioides spores.

Attributable Risk Calculation

To determine the proportion of disease prevented by eliminating exposure, the Attributable fraction needs to be calculated.

Estimate Precision

The precision of relative risk estimates depends on the size of the study.

Avian Influenza Reservoir

The primary reservoir for the highly pathogenic avian influenza H5N1 virus is domestic poultry.

Disease Complexity

The complex interaction among direct and indirect causes of disease is known as a Causal web.

Diagnostic Test Characteristics

When disease prevalence is very low, the positive predictive value of a diagnostic test is lowered.

Norovirus Epidemiology

Most outbreaks of norovirus are due to genotype GII.2, and it is the leading cause of epidemic gastroenteritis globally.

Attributable Risk Calculation Example

Attributable risk can be calculated based on disease outcomes in exposed versus unexposed populations.

IBD and CDI Relationship

Inflammatory bowel disease is associated with increased morbidity and mortality regarding Clostridium difficile infection (CDI).

Tuberculosis in Homeless Individuals

Most TB infections among the homeless are reactivations of established diseases, and sputum testing is highly effective.

Odds Ratios in Case-Control Studies

The odds ratio reflecting the relationship between obesity and Clostridium difficile can be calculated based on provided BMI data.

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Description

Test your understanding of concepts related to the bell curve in statistics. This quiz covers key elements like the proportion of observations within standard deviations and characteristics of nonparametric tests. Challenge yourself with these important statistical foundations!