chapter 3 biostats

Question 1

1, 2, 3 SD around the mean = percents?

Answer 1

68
95
99.7

Question 2

sensitivity test?

Answer 2

true positive / people with disease

for screening

low false negative rate

Question 3

specificity test?

Answer 3

true negatives / people w/o disease

for confirmation of disease

low false positive rate

Question 4

tradeoff between sensitivity and specificity

Answer 4

changing the cutoff for screening
if higher: more FNs, fewer FPs (if higher, you miss more people)
if lower: fewer FPs, more FPs (if lower, you catch more people that are not sick)

Question 5

PPV

Answer 5

probability of having disease given positive test

true positive / all people with positive test

higher prevelance = higher PPV

high sensitivity = low PPV, bc more FPs

Question 6

NPV

Answer 6

probability of not having disease given negative test

true negatives / all negatives

lower prevalence = higher PPV

high sensitivity = high NPV, bc fewer FNs

Question 7

attributable risk

Answer 7

cases attributable to one risk factor = the amount by which the incidence of a test will decrease if the RF is removed

incidence rate in population - incident rate in smokers = attributable risk due to smoking

Question 8

relative risk

Answer 8

compares disease risk in those exposed to a certain factor with the disease risk in people who have not been exposed to the factor

in prospective or experimental studies (not retrospective) cannot be calculated otherwise

significant if NOT 1

1. 5 x more likely to develop disease if exposed to factor in question
2. 5x less likely to develop disease if exposed == protective factor

Question 9

OR

Answer 9

estimates RR in retrospective studies (case control)

Question 10

skewed distribution

Answer 10

meaning not normal distribution

positive skew: lots of high values, tail of the curve is on the right. mean>median>mode

neg skew: lots of low values, tail on left. mean

Question 11

test reliability

Answer 11

=precision
=reproducibility and consistency of test
= random error reducers reliabilitly and precision

Question 12

test validity

Answer 12

=accuracy
=trueness of measurement, does it measure what it claims to measure
=systematic error reduces validity and accuracy

Question 13

define correlation coefficicent

Answer 13

what degree are two variables related
-1 to +1

more strong = absolute value away from 0
if positive = positive correlation
if negative = negative correlation

Question 14

confidence interval

Answer 14

95% certainty that the mean is within this range

1sd - 68
2sd - 95
3sd - 99.7

Question 15

experimental studies
prospective
retrospective
case series
prevalence surveys

Answer 15

order of relevance from best to lowest

Question 16

experimental studies

Answer 16

well matched controls

sometimes ethical c/f is why we can’t do it

Question 17

prospective studies

Answer 17

cohort or observation

dividing groups based on presence of RF and following to determine the outcome

can determine incidnece + RR

Question 18

retrospective studies

Answer 18

choose population samples after the RF

only OR, no incdence + RR

less expensive, better for rare disease

Question 19

case series study

Answer 19

describes presentation of disease, good for rare disease

Question 20

prevalence survey

Answer 20

cross-sectional
prevalence of disease and risk factor
could suggest a cause of disease

Question 21

incidence versus prevalence

Answer 21

incidence=  #new cases of disease in a unit of time
incidence = absolute risk of developing a condition

prevalence = total number of all cases at a point in time

Question 22

what happens to incidence and prevalence if disease can be treated to the point where only people can be kept along longer w/o being cured, what happens?

Answer 22

incidence = nothing
prevalence = goes up

short term diseases = incidence>prevalence
long term = prevalence>incidence

Question 23

nominal = no numeric value (day of week)
ordinal = ranking
continuous data

Answer 23

nominal/ordinal data = use chi square

t-test/anova = continueous data

Question 24

pvalue

Answer 24

if p<0.05, then less than 5% chance that the data were obtained by random error or chance

Question 25

p value error?

Answer 25

type 1 error = claiming an effect when none exists = pvalue percentage

if<0.05, 5% chance of type 1 error

Question 26

type 2 error

Answer 26

claiming no effect when it does exist

Question 27

power

Answer 27

probability of rejecting the null when its false

increase by increasing sample size

Question 28

confounding variables

Answer 28

affect independent and dependent variable

Question 29

nonresponse bias

Answer 29

ppl don’t return surveys

list nonresponders as unknown

Question 30

lead time bias

Answer 30

cancer screening prolongs survival only bc of early detection

Question 31

admission rate bias

Answer 31

comparing MI

hospital A has higher mortality rate bc of higher admission criteria meaning sicker pts

Question 32

recall bias

Answer 32

retrospective studies

overestimate risk factors

Question 33

interviewer bias

Answer 33

absence of blinding

investigator makes an efect when doesnt exist

Question 34

unacceptabilitly bias

Answer 34

pts don’t accept they do bad things so this changes the accuracy of data