Epidemiology:: 2 Module:: Biological Variability

What does standard deviation measure?

the dispersion or spread of a dataset relative to its mean (average)

What is a skewed distribution? 

A distribution where values are not symmetric (mean ≠ median ≠ mode)

What are some examples of biological variables that often follow a normal distribution?

Height and hemoglobin.

What is a percentile?

The value below which a percentage of data falls.

What does a cumulative frequency distribution show?

Shows the number of observations below a particular value.

What is the purpose of a frequency distribution in epidemiology?

Organizes data into intervals to show how often values occur.

What can cause variation in lab values?

Age, sex, ethnicity, hydration, and time of day.

Why can lab reference ranges be misleading?

Healthy and diseased people can overlap in values.

What is a negatively skewed distribution?

Tail to the left; mean < median < mode.

What is a skewed distribution? 

A distribution where values are not symmetric (mean ≠ median ≠ mode)

What is a normal distribution?

A symmetric bell-shaped curve where mean = median = mode.

Give an example of a positively skewed variable.

Income or hospital charges

Give an example of a negatively skewed variable.

Age at death

Which of the following correctly distinguishes cumulative frequency distribution?

A. It shows how often each exact value occurs
B. It organizes data into categories only
C. It shows accumulated observations up to a value
D. It measures disease risk over time

C. It shows accumulated observations up to a value

Which of the following is a limitation of using mean ± 2 SD in clinical practice?

A. It only applies to skewed data
B. Healthy and diseased populations always overlap
C. Not all biological data is normally distributed
D. It eliminates variability completely

C. Not all biological data is normally distributed

According to the empirical rule, approximately 95% of data falls within:

A. ±1 standard deviation
B. ±2 standard deviations
C. ±3 standard deviations
D. ±4 standard deviations

B. ±2 standard deviations

According to the empirical rule, approximately 68% of data falls within:

A. ±1 standard deviation
B. ±2 standard deviations
C. ±3 standard deviations
D. ±4 standard deviations

A. ±1 standard deviation

According to the empirical rule, approximately 99.7% of data falls within:

A. ±1 standard deviation
B. ±2 standard deviations
C. ±3 standard deviations
D. ±4 standard deviations

C. ±3 standard deviations

A positively skewed distribution is characterized by:

A. Tail extending to the left
B. Mean < median < mode
C. Tail extending to the right
D. Symmetric distribution

C. Tail extending to the right

In a positively skewed distribution:

A. Mean = median = mode
B. Mean < median < mode
C. Mean > median > mode
D. Mode > mean > median

C. Mean > median > mode

A child is in the 90th percentile for BMI. This means:

A. The child is at the median BMI
B. 90% of children have higher BMI
C. 90% of children have lower BMI
D. The child has normal BMI

C. 90% of children have lower BMI

A percentile is best defined as:

A. The average value in a dataset
B. The value below which a given percentage of observations fall
C. The most common value in a dataset
D. The difference between two groups

B. The value below which a given percentage of observations fall

What is the cumulative frequency distribution useful for determining?

percentiles, medians, and understanding data spread.

Time to a symptom onset in some acute condition what skewed distribution is this?

negative skewed

Why can reference ranges be misleading in clinical practice?

A. They are always inaccurate
B. Healthy individuals can fall outside the range and diseased individuals can fall inside it
C. They do not include time variables
D. They only apply to lab data

B. Healthy individuals can fall outside the range and diseased individuals can fall inside it

Which statement is TRUE about a skewed distribution?

A. Mean, median, and mode are always equal
B. The data is perfectly symmetrical
C. The mean, median, and mode are not equal
D. The distribution always represents biological variables

C. The mean, median, and mode are not equal