Epidemiology Week 3 Flashcards

1
Q

Describe the nominal measurement scale

A

◾data that can be named and put into categories

◾categories are mutually exclusive and unordered

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2
Q

Describe the ordinal measurement scale

A

◾named data

◾categories are mutually exclusive and ordered

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3
Q

Describe the count/discrete measurement scale

A

◾numeric/measured data

◾specific values, integers

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4
Q

Describe the continuous measurement scale

A

◾numeric/measured data

◾data that can take on any value

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5
Q

What is central tendency?

A

measures of location (ex. mean, median)

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6
Q

Give four measures of central tendency

A

◦Mean - arithmetic average
◦Median - middle value of sorted data, less influenced by outliers
◦Mode - most frequent value
◦Geometric mean - nth root of the product of the data

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7
Q

What is variability?

A

measures of spread (ex. range, std dev)

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8
Q

Give different measures of variability

A

◦Range - max value - min value
◦Interquartile range - 75th percentile - 25th percentile
◾Captures central 50% of the data
◦Variance - average squared deviation from the mean
◦Standard deviation - square root of variance
◦Coefficient of variation - standard deviation/mean

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9
Q

What are the major sources of variation?

A
◦Biologic variation
   ◾Between-individual
   ◾Within-individual
◦Measurement variation
   ◾Between-observer
   ◾Within-observer
◦Instrument or analytical error
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10
Q

What is reliability?

A
  • Precision

- Random error

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11
Q

What is validity?

A
  • Accuracy

- Systematic error

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12
Q

How is data displayed graphically?

A
  • Histograms
  • Box charts
  • Bar charts/Pie charts
  • Distribution curves
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13
Q

Give the properties of normal distribution curves

A

◾Bell shaped
◾Total area under curve = 1
◾Extends to infinity in both directions
◾Probability corresponds to area under the curve
•68% within +/- 1 standard dev of mean
•95% within +/- 2 standard devs of mean
•99% within +/- 3 standard devs of mean
◾Only need to know mean and standard dev

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14
Q

What is sensitivity:

A

Proportion of those with disease who also have a positive test result
Sensitive test means TP/(TP + FN) close to 100%
few false negatives
most negative results are true

SNOUT (Sensitive test with negative result rules out disease)
Sensitivity and negativity both have Ns in them

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15
Q

Specificity

A

Proportion of those without the disease who give a negative test result
Specific test means TN/(TN+FP) close to 100%
gives few false positives
most positive results are true
Patients with positive results likely have the disease
SPIN = Specific test with Positive results rules in disease
Specificity and positive both have Ps in them

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16
Q

False positive and false negative

A

If FN is worse than FP use a sensitive test

If FP worse than FN, use a specific test

17
Q

Positive predictive value

A

Calculate the probability of the patient having the disease given a positive test result
TP/(TP+FP)
prevalence is positively associated with +PV (prevalence increases, +PV increases)

18
Q

Negative predictive value

A

Calculate the probability of the patient not having the disease given a negative test result
TN/(FN+TN)
prevalence is negatively associated with -PV (prevalence increases, -PV decreases)

19
Q

Use properties of the normal (Gaussian) distribution and the standard normal (Z) distribution to estimate probabilities of clinical events:

A

normal (Gassian) distribution: describes frequency distribution of repeated measurements of the same physical object by the same instrument
standard normal distribution:
- curve is symmetrical and bell-shaped
- two-thirds of observations fall within 1 standard deviation of mean
- 95% of observations fall within 1 standard deviation of the mean

20
Q

Methods to determine reference intervals: normal distribution method

A

mean +/- 2x standard deviation
68% within +/1 1 standard dev of the mean
95% within +/- 2 standard dev of the mean
99% within +/- 3 standard dev of the mean

21
Q

Transformation method:

A

transform values to make data more like a normal distribution using logs
use the normal distribution method

22
Q

Percentile method:

A

assumes no distributional form
works for any distribution (nonparametric)
sample data should be representative of reference population
sample size should be large enough so estimates of range will be reliable