Biostat

Question 1

what is the Hawthorne effect?

Answer 1

tendency of study subjects to change their behavior as a result of their awareness that they are being studied

Question 2

what is Berkson’s bias

Answer 2

selection bias created by choosing hospitalized patients as the control group- selected from hospital is less healthy than the general population

Question 3

what is Pygmalion effect

Answer 3

researcher’s beliefs in the efficacy of treatment can potentially affect the outcome

Question 4

what is the chi-square test for independence used for?

Answer 4

evaluate the association between 2 categorical variables

Question 5

positive predictive value

Answer 5

answers the question: if the test result is positive, what is the probability that a patient has the disease

PPV= TP/ (TP+FP)

Question 6

what is the analysis of variance (ANOVA) used for?

Answer 6

determine whether there are any significant differences between the means of 2 or more independent groups

reject the null when there are at least 2 group means that are significantly different from one another

Question 7

how to calculate power

Answer 7

1-beta

power indicates the probabilty of seeing a differnce when there is one

beta= type II error: the probability of concluding there is no difference between groups when one truly exists

Question 8

attributable risk percent in the exposed

Answer 8

excess risk in an exposed population that can be explained by exposure to a particular risk factor

=100X[(RR-1)/RR]

RR- relative risk

Question 9

ecological study

Answer 9

unit of analysis in the study is populations not individuals

Question 10

odds ratio

Answer 10

measure of association that compares odds of an outcome occurring based on exposure status

OR= ad/bc

Question 11

absolute risk reduction:

Answer 11

event rate in control group-event rate in the treatment group

if 8% who got vaccine got infected vs 2% who didn’t get vaccinated got infected–> 8-2=6%

Question 12

how to use Hardy-Weinberg to estimate carrier frequency, disease frequency, and frequency of different genotypes

Answer 12

allele frequence: p+q=1

p=normal allele frequency
q= mutant allele frequency

phenotypic frequency: p^2+2pq+q^2=1

2pq=carrier frequency

calculating mutant allele frequency from disease prevalence: √q^2=q

q^2= disease prevalence

Question 13

how does skewness affect mean, median, and mode

Answer 13

negatively skewed: mean

Question 14

cross-sectional study

Answer 14

frequency of disease and frequency of risk-related factors are assessed in the present (what is happening)

snapshot study

Question 15

case-control study

Answer 15

compares a group of people with disease to a group without disease

looks to see if odds of prior exposure or risk factor differs by disease state

“what happened”

Question 16

crossover study

Answer 16

subjects as as their own control where they are randomly given a sequence of 2 or more treatments taken consecutively. try treatment A then washout period then try treatment B

Question 17

case series

Answer 17

descriptive study that tracks patients with a known condition to document the natural history or response to treamtent

Question 18

number needed to harm

Answer 18

number of people who must be treated before 1 additional adverse event occurs

1/ absolute risk increase (aka attributable risk)

ARI= 60%-40%=example

Question 19

specificity

Answer 19

TN/(TN+FP)

Question 20

sensitivity

Answer 20

TP/(TP+FN)