Lecture 6 (Normal)

Question 1

Why do we have cut-off points?

Answer 1

• clinical variables are continuous, but physicians need to make dichotomous decisions

Question 2

Distribution and range of normal values and cutoff points appropriate for a particular individual often depends on such factors as:

Answer 2

1. age
2. sex
3. race
4. occupational and environmental exposure history
5. other medical conditions
6. other factors that modify risk or response to therapy

Question 3

Abnormal can be defined as:

Answer 3

1. Unusual
2. Associated with disease/increased disease risk
3. treatment does more good than harm
4. >2SD from mean of reference population

Question 4

The cut-off point for abnormal is typically:

Answer 4

• +/- 2SD from mean of reference population.

Question 5

Normal distribution:

Answer 5

• classic bell curve
• highest density in middle, tapers off on both sides
• mean, median, and mode all in the same place (dead center of bell curve)

Question 6

Right skewed distribution:

Answer 6

• tail/outliers on the right of the bell; RIGHT TAIL
• highest density on the left, tapers out toward the tail
• Mode is where the bell peaks; mean is far in the tail. Median in middle.

Question 7

Left skewed distribution:

Answer 7

• tail/outliers on the left of the bell; LEFT TAIL
• highest density on the right (where the bell is), tapers out toward the tail
• Mode is where the bell peaks; mean is far in the tail. Median in middle.

Question 8

Bimodal distribution:

Answer 8

• think of breasts - there is a variable (like sex; M/F) under the bimodal curve
• highest density at both bells, tapers off in each direction evenly
• bimodal has two “density centers”

Question 9

Mean, median, mode in relation to skew:

Answer 9

• Mode is insensitive to skew
• Median moderately influenced
• Mean most sensitive to skew

Question 10

Standard deviation:

+/- 3SD contains –% of observations

Answer 10

99.7%

Question 11

Standard deviation:

+/- 1SD contains –% of observations

Answer 11

68%

Question 12

Standard deviation:

+/- 2SD contains –% of observations

Answer 12

95%

Question 13

Distributions can be summarized by:

Answer 13

• central tendency
  
  • mean, median, mode
• dispersion
  
  • range, standard deviation, percentiles, and quartiles

Question 14

A patient’s test result may fall outside the reference range for what reasons (4)?

Answer 14

1. Analytic error
2. Inter-individual variability
3. Intra-individual variability
4. Disease process or increased risk of disease

Question 15

The three types of variables:

Answer 15

• nominal
  
  • categorical: yes/no, male/female, etc.
• ordinal
  
  • ranking (high/low)
• interval
  
  • continuous (any number)
  • discrete (counts)

Question 16

The three types of variation:

Answer 16

• Overall variation:
  
  • measurement variation + biological variation
• Measurement variation:
  
  • instrument variation + observer variation
• Biological variation:
  
  • intra-individual and inter-individual

Question 17

Overall variation =

Answer 17

measurement variation + biological variation

Question 18

Measurement variation =

Answer 18

instrument variation + observer variation

Question 19

Biological variation =

Answer 19

intra-individual and inter-individual

Question 20

What is considered normal?

Answer 20

1. within 2SD of reference population mean
2. not at an increased risk for an adverse event
3. treatment does more harm than good
4. political and cultural values