# Lecture 6 (Normal) Flashcards

1
Q

Why do we have cut-off points?

A
• clinical variables are continuous, but physicians need to make dichotomous decisions
2
Q

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

A
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
3
Q

Abnormal can be defined as:

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

The cut-off point for abnormal is typically:

A
• +/- 2SD from mean of reference population.
5
Q

Normal distribution:

A
• 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)
6
Q

Right skewed distribution:

A
• 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.
7
Q

Left skewed distribution:

A
• 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.
8
Q

Bimodal distribution:

A
• 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”
9
Q

Mean, median, mode in relation to skew:

A
• Mode is insensitive to skew
• Median moderately influenced
• Mean most sensitive to skew
10
Q

Standard deviation:

+/- 3SD contains –% of observations

A

99.7%

11
Q

Standard deviation:

+/- 1SD contains –% of observations

A

68%

12
Q

Standard deviation:

+/- 2SD contains –% of observations

A

95%

13
Q

Distributions can be summarized by:

A
• central tendency
• mean, median, mode
• dispersion
• range, standard deviation, percentiles, and quartiles
14
Q

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

A
1. Analytic error
2. Inter-individual variability
3. Intra-individual variability
4. Disease process or increased risk of disease
15
Q

The three types of variables:

A
• nominal
• categorical: yes/no, male/female, etc.
• ordinal
• ranking (high/low)
• interval
• continuous (any number)
• discrete (counts)
16
Q

The three types of variation:

A
• Overall variation:
• measurement variation + biological variation
• Measurement variation:
• instrument variation + observer variation
• Biological variation:
• intra-individual and inter-individual
17
Q

Overall variation =

A

measurement variation + biological variation

18
Q

Measurement variation =

A

instrument variation + observer variation

19
Q

Biological variation =

A

intra-individual and inter-individual

20
Q

What is considered normal?

A
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