Flashcards in Biostats Deck (39):

1

##
Cross sectional study?

Case control study?

Cohort study prospective

cohort retrospective?

Measures and examples for each.

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Cross sectional study?

groups of people to assess frequency of a disease and risk factors at a point in time.

Disease prevalence

Risk factor association with disease

Case control study?

Group of people with disease to group of people without

Prior exposure of risk factor

Odds ratio

Cohort study prospective?

Group of people with a given exposure or risk factor to a group without

Does exposure incr. likelihood of disease

Relative risk

Who will develop disease?

cohort retrospective?

Same as above but who did develop disease?

2

## What is size and purpose of phase I, II, III, and IV of clinical trial?

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I-small number of healthy volunteers; is it safe?

II-small number of pts with disease; does it work?

III-large number of pts randomly assigned to treatment or placebo; is it as good or better?

IV-postmarketing surveillance; can it stay?

3

## What is sensitivity? How is it calculated? Purpose?

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proportion of all people with disease who test positive.

Probability that a test detects disease when disease is present

Out of all the people with the disease, how many does it catch?

TP/(TP + FN)

1- FN rate

SN-N-OUT

Sensitive test, when negative, rules out disease (no false negatives)

4

## What is specificity? How is it calculated? Purpose?

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Proportion of all people without the disease who test negative

Probability that a test indicates no disease when disease is absent

Out of all the people without the disease, how many does the test say don't have the disease?

TN/ (TN + FP)

1-FP rate

SP-P-IN

Highly specific test, when positive, rules in (no false positives)

5

## What is a PPV? Calculaton? How does prevalence/pretest prob affect it?

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TP/(TP + FP)

Probabilty that person actually has disease given a positive test result

Varies directly with prevalence or pretest prob

6

## What is a NPV? Calculaton? How does prevalence/pretest prob affect it?

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TN/(TN+FN)

Probability that a person actuallly is disease free given a negative test result

Varies inversely with prevalence or pretest prob.

7

## Describe a 2x2 contigency table for quantifying risk.

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Disease on top axis, risk factor or intervention on side

+ -

+ ab

- cd

8

## What is an odds ratio? When is it used? Calculation?

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Case control

Odds that group with disease was exposed to risk factor (a/c) divided by odds that group without the disease was exposed (b/d)

(a/c)/(b/d) OR ad/bc

9

## What is an relative risk? When is it used? Calculation?

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Cohort studies

Risk of developing disease in the exposed group divided by risk of developing disease in the unexposed group.

a/(a+b)/c/(c+d)

21% chance/1% chance

10

## What is AR? Calculation?

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Attributable risk

Difference in risk b/w exposed and unexposed groups, or proportion f disease occureces that are attributable to exposure.

a/(a+b)-c/(c+d)

21% chance - 1% chance

11

## What is the relative risk reduction? Calculation?

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proportion of risk reduction attributable to intervention as compared to control

RRR=1-RR

12

## What is ARR? Calculation?

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c/(c+d) - a/(a+b)

Difference in risk, not proportion attributable to intervention as compared to control.

13

## What is the NNT? calc? NNH? calc?

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number of patients needing to be treated for one to benefit

1/ARR

Number of pts. treated before someone is harmed?

1/AR

14

## How does precision affect SD? How does it affect power? What decreases accuracy in a test?

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Incr. prec. decr. SD

Incr. prec. incr. statistical power

Systematic error or bias.

15

## What is selection bias? Examples? Strategy to reduce?

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Error in assigning subjects to study group resulting in unrepresentative sample. Most commonly a sampling bias

Berkson=selected from hospital, not general popul

healthy worker=study population healthier than general

non-response=participating subjects differ frm non particpating in meaningful ways

Randomization

Ensure the choice of the right comparison/reference group

16

## What is recall bias? Examples? Strategy? Measurement bias? Same questions? Procedure? Observer-expectancy?

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RECALL

Awareness f disorder alters recall by subjects; common in retrospective studies

Pts with disease recall exposure after learning of similar cases

Decr. time from exposure to F/U

MEASUREMENT

info in gathered in way that distorts it

Miscalibrated scale

Standard method of data collection

PROCEDURE

Subjects in groups not treated the same

Pts in treatment group spend more time in hospital units

Blinding, use of placebo

OBSERVER-EXPECTANCY

Researchers belief in the efficacy of treatment changes outcome

Pygmalion effect, self-fulfilling prophecy

Observer more like to document positive outcomes if he expects treatment to work

blinding, use of placebos

17

## What is confounding bias? Examples? Strategy? Lead time bias?

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CONFOUNDING

Factor related to both exposure and outcome, but not on causal pathway

Pulmonary disease is amore common in coal workers, but coal workers also smoke more

Multiple/repeated studies

Cross over studies

matching

LEAD TIME BIAS

Early detection is confused with incr. survival

Measure back end survival (adjust according to severity at time of diagnosis)

18

## What is the mean? Median? Mode? Which is least effected by outliers? Most affected by outliers?

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Mean=most affected by outliers

Median-middle value of list

mode=most common value, least affected by outliers

19

## What is standard deviation? Standard error of the mean? Calculation? What causes SEM to decr ?

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SD-how much variability exists from the mean in a set of values

SEM=an estimate of how much variability exists between the sample mean and the true population mean.

SD/sq.rt (sample size)

SEM decr. with incr. sample size

20

## What is normal distributin? What percentage falls within 1 SD? 2SD? 3SD?

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Mean=median=mode

1SD=68%

2SD=95%

3SD=99.7%

21

## What is bimodal distribution? Positive skew? Negative skew?

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Two different populations

Mean > median > mode

positive outliers cause a longer tail on right

mean< medinegative outliers cause longer tail on left

22

## What is the null hypothesis? Alternative?

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H0=Hypothesis of n difference or relationship

H1=Hypothesis f sme difference or relationship (not due to chance)

23

## What is a type I error? What is alpha? What is p?

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There is an effect or difference when none exists (null hypothesis rejected when it should not have been).

Alpha is probability of making a type I error

p is judged against a preset alpha. If p <.05, there is a less than 5% chance of making a type I error

False positve error

You sAw a difference that did not exist

24

## What is a type II error? What is Beta? What is power? What can incr. power?

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Stating there is no effect when there is one.

Beta is prob of making a type II error

Power=1-beta, which is the probability of not getting a type II error (finding an effect if there is one)

You were Blind to the truth

Incr power by:

Incr. sample size

Incr. expected effect size

incr. precision of measurement

25

## What is a confidence interval? What is the Z score for 95% CI? 99% CI? How is it used in accepting or rejected H0 in calculating mean differences? In Odds ratio or Relative risk?

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Mean +/- Z (SEM)

95% CI, Z=1.96

99%CI, Z=2.58

In comparing means, if difference CI does not include zero, reject HO

In odds ratio, if CI does not include 1, reject HO

If CIs b/w two groups overlap, likely no difference

26

## What is a t-test? ANOVA? Chi-square?

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Checks differences of means in 2 groups

Differences of means in 3 or more groups

Differences between 2 or more percentages or proportions of categorical outcomes.

"chi"tegorical

percentages of 3 different ethnic groups with hypertension.

27

## What is the pearson correlatin coefficient? Range? What does it mean? What is the coefficient of determinatin?

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r between -1 and +1

Closer to 1, better the correlation

Negative is negative correlation

r^2

28

## Waht is primary disease prevention? Secndary? Tertiary?

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Prevent

Screening

Treating

29

## What are the 4 parts of medicare?

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part A=hospital insurance

part B=Basic medical bills

Part C= (parts A and B) delivered by approved companies

Part D=prescription drugs

30

## What are the 4 parts of informed consent? Waht are some exceptions?

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Disclosure: risks/benefits, can always revoke consent

Understanding: ability to comprehend

Capacity: ability to make decisions, reason

Voluntariness: no coercion

Patient lacks decision making capacity or is legally incompetent

Implied consent in emergency

Therapeutic privilege-withholding inf when disclosure would severly harm patient of undermind informd decision making capacity

Waiver-pt. explicity waves the right of informed consent

31

## What is a minor? When is is parental consent not required?

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under 18

Sex (contraception, STIs, pregnancy)

Drugs (addiction)

Rock and roll (emergency, trauma=even if it opposes parent's religious beliefs)

Always encourage communication in these situations

32

## What are the aspects of decision making capacity?

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pt is > 18 years old or legally emancipated

makes and communicates a choice

is informed

Decision remains stable over time

consistent with values and goals (not clouded by mood)

not a result of altered mental status

33

## What makes an oral advance directive more valid? What is a living will? What is medical power of attorney? When can it be revoked?

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patient was informed

directive specific

patient made a choice

repeated over time to multiple people

Written advanced directive

describes treatments patient wishes to receive or not receive in certain circumstances

Agent designated to make decisions if they lose capacity

May also specify decisions in certain situations

Can be revoked at any time (even if not competent)

34

## Order of surrogacy? When are they need?

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Lose capacity and no advanc directive

spouse, adult children, parents, adult siblings, other relatives

35

## Waht are some exceptions to confidentiality? Examples?

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Potential physical harm to others is serious or imminent

Likelihood of harm to self is great

No alternative means exists to warn others

Physicians can take steps to prevent harm

reportable diseases

Tarasoff decision=protect potential victim from harm

child and/or elder abuse

impaired auto drivers (epileptics)

Suicidal/homicidal patients

36

## What is the apgar score based on? Timing? Score/interpretation?

### Appearance, pulse, grimace, activity, respiration (>=7 is good, 4-6-assist and stimulate, <4 at a later time, incr. risk of long term neuro damage

37

## What is defined as low birth weight? Cause? Associations? Problems? complications?

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<2500 g

Prematurity or IUGR\

Incr. risk of SIDS and overal mortality

Impaired thermoregulation, immune function

hypoglycemia

polycythemia

impaired neurocogn/emotional development

Infections, NRDS, NEC, IVH, Persistent fetal circulation

38

## What are some sexual changes that occur in the elderly men and women? How do sleep patterns change? What other changes occur? What does not change? What is presbycusis? Explain it.

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Men-slower erection/ejaculation, longer refractory period

women-vaginal shortening, thinning, and dryness

Decr. REM and slow wave sleep; incr. sleep onset latency and incr. early awakenings

Incr. suicide rate

Decr. visin, hearing, immune response, bladder control

Decr. renal, pulm, and GI function

Decr. muscle mass

Incr. fat

Sexual interest does not decr.

Intelligence does not decr.

presbycusis=sensorineural hearing loss (often higher frequencies) due to destruction of hair cells at base.

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