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Biostats > Exam 2 BIO > Flashcards

Exam 2 BIO Flashcards

1
Q

Case control

A

disease is rare and exposure is common

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2
Q

Cohort

A

disease is common and exposure is rare

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3
Q

case-control

A

disease has a long latent period and the exposure information is very expensive to obtain

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4
Q

odds ratio

A

AD/BC

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5
Q

interpreting odds ratio

A

compared to normal, patients with ___ had 3.9 times the odds of having _____

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6
Q

measures of association

A

comparison of disease frequency

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7
Q

absolute measure

A

calculate difference between 2 measures of disease freqeuncy

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8
Q

relative measure

A

calculate the ratio of 2 measures of disease frequency

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9
Q

if there is NO association between the exposure and disease then,

A

RD=0

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10
Q

if the exposure is associated with increased risk of disease then,

A

RD>0

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11
Q

if the exposure is associated with DECREASED risk of disease then,

A

RD<0

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12
Q

Cumulative Incidence (CI) -Risk difference

A

Exposed (Disease) -Unexposed (No Disease)

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13
Q

If RR is less than 1 (like 0.55), then

A

(1-RR), so 1-0.55=0.45—–45% decrease in risk (in whatever like getting a vaccine)

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14
Q

Risk Ratio

A

Ratio of cumulative incidence between (exposed/unexposed)

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15
Q

Excess Relative Risk

A

(RR-1) X 100%—-meaning ___ % have an increased risk

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16
Q

RD is Absolute Measure

A

Represents measure of public health impact of exposure on disease occurrence

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17
Q

RR is Relative Measure

A

Represents measure of strength or magnitude of the association between an exposure and a disease—-used in etiologic research

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18
Q

There are 2 types of epidemiology

A

Descriptive and Analytic/Scientific

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19
Q

Descriptive

A

-Identifies and counts cases of disease/population according to person, place, time
Case reports and series
Cross-Sectional study
Ecologic Study

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20
Q

Analytic/Scientific

A

-Compares group and systemically determine if there is association
Clinical trial
Experimental Study
Case-Control Study
Cohort Study

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21
Q

Prospective Cohort Study

A

Weakness: -More expensive, time consuming, and not efficient for diseases with long latent periods
Strength: Better exposure and confounder data and less vulnerable to bias

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22
Q

Retrospective Cohort Study

A

Weakness: Exposure and confounder data may be inadequate and more vulnerable to bias
Strength: Cheaper, faster and efficient with diseases with long latent period
Start of the study: Compare incidence of disease

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23
Q

Cohort Study Limitations

A

may need large number of subjects to be followed for long periods of time-difficult, expensive and time consuming
Undermines validity (loss to follow)
Not good for rare diseases/long latency
Not good when exposure data are expensive to obtain

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24
Q

Case-Control Study

A

Investigator identifies cases and selects controls who represent a sample of the population —>compares exposures

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25
Q

Cohort Study

A

Investigator identifies exposed and unexposed groups—->compares incidence of outcome

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26
Q

When to conduct a case-control study?

A

-When exposure data are expensive or difficult to obtain
-when disease has long latent period/decades for results
-disease is rare
-population is difficult to follow/high loss
-little is known about the disease/need to evaluate many exposures

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27
Q

Case control studies need source population:

A

FIxed or Dynamic but are good in dynamic populations

28
Q

Controls

A

to estimate the exposure distribution in source population that produced the cases
must come from same source population
must be selected independently of exposure

29
Q

Would Criterion

A

Would it be enrolled as a case? if yes then selection bias is unlikely
To be yes: controls need to have SAME population as the cases that were selected

30
Q

Nested Controls

A

Controls selected from an existing cohort population (sub-set)

31
Q

Population Based Controls

A

Controls selected from general population-suitable when cases are from well defined geographic area

32
Q

Hospital or Clinic Based Controls

A

Controls selected from among patients at a hospital or clinic
(should be unrelated to exposure , should not cause the exposure)

33
Q

3 ways to sample controls in case-control study

A
  1. survival sampling
  2. Case-Cohort Sampling
  3. Risk-Set Sampling
34
Q

Survivor Sampling

A

Select Controls at END of follow-up

35
Q

Case-Cohort Sampling

A

Select controls from starting Cohort at beginning of follow-up

36
Q

Risk-set sampling

A

Longitudinally select controls as cases arise during follow-up

36
Q

Risk-set sampling

A

Longitudinally select controls as cases arise during follow-up

37
Q

Case-Control Studies Strength

A

Fewer ethical concerns, more efficient than cohort study (less time, fewer subjects needed, no need to wait for long latency diseases to develop), easy to explore effect of many exposures on an outcome (ID outbreak, or disease with little info)

38
Q

Case-Control Studies Limitation

A

limited to a single outcome, inefficient for rare exposures, more opportunity for systematic bias, cannot calculate absolute measure of association

39
Q

Nonparametric tests

A

when data is not normally distributed

40
Q

When to use nonparametric tests

A

-when sample size is too small
-when data has outliers that cant be removed
-when you want to test for median rather than the mean (skewed distribution)
-Outcome is continuous and not normally distributed

41
Q

Non-parametric tests include:

A

Spearman Rank Correlation, 1-sample sign test, mann-whitney test, wilcoxon signed rank test, kruskal-wallis test, friedmans ANOVA

42
Q

Use nonparametric if sample size:

A

Less than 20

43
Q

Mann-Whitney U test

A

Test 2 independent samples with the dependent ordinal/continuos not assumed to follow a normal distribution
If H0 (null) two populations are equal; if H1 , two populations are not equal

44
Q

Sign Test (pos/neg)

A

-Continuos outcome measured in matched or paired samples
-SUBTRACT After - Before
-Can be used for ordered (ranked) categorical data
H0=Median difference is zero
H1=Median difference < or > zero
Reject H0 if the smaller of the number of pos/neg signs is less than or equal to the critical value

45
Q

Wilcoxon Signed Rank Test

A

-Examines signs, score differences, and magnitude of observed difference
-SUBTRACT Before - After
-Test statistic is W and we use the smaller of W+ and W-
Reject H0 if W is < or = to critical value

46
Q

Kruskal Wallis Test

A

sample size does not need to be equal
K>2
H0=K population median are equal
H1=K population median are not equal
Test statistic is H
Reject H0 if H is >/= critical value

47
Q

logistic regression

A

used when the independent variables include both numerical and nominal measures and the outcome variable is BINARY (Dichotomous)
-YES/NO
-Sruvived/Deceased

48
Q

Logistic Regression Variables:

A

Two Indepedents: X1=dichotomous and X2=Continuous
Outcome Variable: Y=Dichotomous

49
Q

Odds Ratio

A

If OR is >1: greater odds of association of exposure and outcome
If OR=1: there is no association between exposure and outcome
If OR<1: there is a lower odds of association
If CI includes 1 then results are not statistically significant

50
Q

If OR=1.2

A

1-1.2 times 100=20% chance increase in odds of an outcome happening

51
Q

If CI includes 1 then

A

cant be significant because can be either lower or higher cant pick a side in other words

52
Q

Analyzing Hazard Ratio: HR=0.87

A

(1-HR)X 100= 13% reduction

53
Q

Survival Analysis

A

situations where the outcome is the length of time that elapses until the event of interest occurs
For example:
1. Length of time until death following diagnosis of a disease
2. Length of time to cancer remission
3. Length of time until death following initiation of therapy

54
Q

Survival Analysis what does it measure?

A

Outcome is time to event
measures whether person has event or not (Yes/No) and time to event
estimate survival time
determine factors (pt characteristics) associated with longer survival

55
Q

survival analysis used to:

A

determine if the risk of experiencing a particular event over a specific period of time differs between groups

56
Q

Log rank test

A

determines if the difference between two survival curves is statistically significant
-the larger the difference, the more likely it is statistically significant

57
Q

Survival Curves:

A

Estimated using Kaplan-Meier Method and compared statistically using log-rank test

58
Q

hazard ratio

A

measures an effect of the intervention on an outcome of interest over time

59
Q

If negative outcome (death) and hazard ratio <1:

A

this is desirable and is a percent reduction in risk
if HR was 0.25, then 75% were less likely to die

60
Q

Cox Proportional Hazards Regression Model

A

outcome is still time to event but it is an extension to survival analysis by including control variables in the regression model

61
Q

Repeated Measure ANOVA

A

technique used to test equality of means
-Need to measure 3 items

62
Q

When to use repeated Measure ANOVA

A

measuring performance on the same variable over time
(changes in performance in training or after a treatment)
-same subject is measured multiple times under different conditions
-same subject provides measures/ratings on different characteristics

63
Q

superior trial

A

aims to show that the new drug is better than standard treatment
-like traditional hypothesis testing
-if 0 is not contained within the CI we can reject H0–>concluding new drug is superior

64
Q

Non-inferiority Trial

A

Aims to show that the new drug is no worse (not inferior) than standard treatment (existing med) by a prespecified amount.
Prespecified amount=non-inferiority margin and is sometimes expressed as M
-There is no placebo group: control group takes existing medication that already demonstrated effectiveness
-compare CI to M2 and to zero

65
Q

two noninferiority margins (M1 and M2):

A

M1 reflects the difference between control drug and placebo. Reflects the full efficacy of control drug
M2 a smaller amount that reflects how much efficacy the investigators are willing to give up in return for other advantages the new drug may offer.(like improved safety)

66
Q

Equivalence Trials

A

aims to show that the new treatment is no better and no worse
-rejecting the H0 is equivalent to concluding that the test drug and control drug DO NOT DIFFER from one another

Biostats (4 decks)

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