Stats

Question 1

Count

Answer 1

Cannot be compared b/c they arise from populations of different sizes
Use when important to public health or to allocate resources

Question 2

Ratio

Answer 2

Shows relative size of 2 values

Question 3

Proportion

Answer 3

Numerator is subset of denominator
Dimensionless
Between 0 and 1

Question 4

Rate

Answer 4

a/a+b (can be proportion, always a ratio) over an amount of time

Question 5

Incidence

Answer 5

Frequency of the occurrence of new cases over a specified period of time
Measures appearance of disease

Question 6

Cumulative incidence

Answer 6

Risk of probability of an individual getting a disease
Proportion: # of new cases of disease/# at risk at beginning of follow up or over a specified time period
Fixed populations

Question 7

Incidence rate

Answer 7

# of new cases/sum of disease-free person-time over specified time period
Takes into account population differences in periods of follow up

Question 8

Person-time at risk

Answer 8

Sum of disease-free time in population

1. Add individual risk periods (exact)
2. Use average number of people multiplied by study duration
3. Use average duration per person

Question 9

Prevalence

Answer 9

Proportion of people in a population w/ the disease at a specified point in time
Measures existing disease
Describes health burden

Question 10

Point prevalence

Answer 10

Proportion: # of existing cases/total population at a specified point in time

Question 11

Period prevalence

Answer 11

Proportion: (# of existing cases + # of cases that occur during the interval)/population at midpoint of interval or avg population size

Question 12

Prevalence-Incidence relationship

Answer 12

Prevalence depends on incidence and disease duration
P = ID
If a disease is of short duration, I ~ P
If a disease is chronic, P > I
Prefer incidence b/c interested in etiology and you don’t want to vary too many factors at the same time (birth defect problem)

Question 13

Binary data

Answer 13

One of two answers

Question 14

Nominal data

Answer 14

Categorical data w/ no order

Question 15

Ordinal data

Answer 15

Categorical data w/ order

Question 16

Continuous data

Answer 16

Data measured continuously or on integer scale

Question 17

Frequency distribution

Answer 17

Means of describing categorical data

Must add up to 100%

Question 18

Mean

Answer 18

Average

Limitations: sensitive to extreme values, not ideal for skewed data

Question 19

Median

Answer 19

Middle value

Question 20

Mode

Answer 20

Most often

Question 21

Variance

Answer 21

Average of square of deviations about the sample mean

S^2 = (sum(xk -xbar)^2)/(n-1)

Question 22

Negative skew

Answer 22

Number of outlying values on low end (hump is on right)

Question 23

Positive skew

Answer 23

Number of outlying values on high end (hump is on left)

Question 24

Standard deviation

Answer 24

Square root of variance

Std = sqrt((sum(xk -xbar)^2)/(n-1))

Question 25

Normal distribution

Answer 25

Theoretical probability distribution that is symmetric about its mean and is "bell" shaped Mean = Median = Mode

Question 26

Standard normal distribution

Answer 26

Specific distribution with mean of 1 and Std of 1 68% of data w/in 1 std 95% of data w/in 2 std 99.7% of data w/in 3 std

Question 27

Shapiro-Welk test

Answer 27

Null hypothesis = data are normally distributed | p < 0.05 means data are NOT normally distributed, reject null hypothesis

Question 28

Screening

Answer 28

Presumptive identification of unrecognized disease or condition by application of tests, examination, or other procedures Attempts to classify asymptompatic people as likely or unlikely to have disease Goal is to delay onset of symptoms and prolong survival Only done for healthy people

Question 29

Primary Prevention

Answer 29

prevent disease before it starts

Question 30

Secondary Prevention

Answer 30

delay symptoms

Question 31

Tertiary Prevention

Answer 31

slow disease progression

Question 32

Lead Time

Answer 32

duration of time by which diagnosis is advanced as a result of screening

Question 33

Validity

Answer 33

Does the test measure what it's supposed to measure? | Bullseye

Question 34

Internal validity

Answer 34

Does the test measure what it's supposed to measure?

Question 35

External validity

Answer 35

Generalizability, how well does the result generalize to the population?

Question 36

Reliability

Answer 36

Does the test give the same result over and over?

Question 37

Sensitivity

Answer 37

Sensitivity = a / a + c Number of people who screen positive over number of people who actually have the disease Increase to prevent disease transmission Sensitivity + FN = 1

Question 38

Specificity

Answer 38

Specificity = d / b + d Number of people who screen negative amongst those who don't have disease Increase for fatal disease w/ no treatment Specificity + FP = 1

Question 39

True positive

Answer 39

Individuals who test positive and have disease

Question 40

True negative

Answer 40

Individuals who test negative and don't have disease

Question 41

False positive

Answer 41

Individuals who test positive and don't have disease Increased w/ increasing sensitivity FP = b / b + d Specificity + FP = 1

Question 42

False negative

Answer 42

Individuals who test negative and half disease Increased w/ increasing specificity FN = c / a + c Sensitivity + FN = 1

Question 43

Overall Accuracy

Answer 43

Assesses proportion of true test results among all test results Overall accuracy = A + D / A + B + C + D = TP + TN / TP + FP + TN + FN

Question 44

Positive predictive value

Answer 44

Number of people w/ true disease who tested positive divided by number of people who tested positive Likelihood of having true disease if you test positive PPV = a / a + b

Question 45

Negative predictive value

Answer 45

Number of truly non-diseased people who tested negative divided by number of people who tested negative Likelihood of not having disease if you test negative NPV = d / c + d