# 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

- age
- sex
- race
- occupational and environmental exposure history
- other medical conditions
- other factors that modify risk or response to therapy

3

Q

Abnormal can be defined as:

A

- Unusual
- Associated with disease/increased disease risk
- treatment does more good than harm
- >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

- Analytic error
- Inter-individual variability
- Intra-individual variability
- 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)