Epidemiology and ethics

Question 1

Sensitivity

Answer 1

TP/(TP+FN)
True positve rate, all negatives are TN
To screen disease, if negative, SNOUT

Question 2

Specificity

Answer 2

TN/(TN+FP)
True negative rate, all positive are TP
To confirm disease, if positive, SPIN

Question 3

Case-control study

Answer 3

Observation, retrospective
“What happened?”
Uses ODD RATIO (OR)

Question 4

Cohort study

Answer 4

Observation, either prospective or retrospective
Who will develop disease, or who developed disease?
Uses RELATIVE RISKS (RR)

Question 5

Cross-section study

Answer 5

Observation
“What’s happening”
Determines disease prevalence (DP)
***association but not necessarily causation

Question 6

Clinical trials

Answer 6

1: few healthy volunteers: safety, toxicity, PK
2: few diseased pts: efficacy, optimal dosing, adverse effect
3: large number of pts: new tx vs current standard of care
4: postmarketing surveillance: detects rare, long term effect

Question 7

PPV and NPV

Answer 7

PPV: high pretest prob => high PPV
NPV: high pretest prob => low NPV

Question 8

Incidence vs. prevalence

Answer 8

Incidence rate: # new cases in a time/ pop at risk during the same time period
Prevalence: # exisiting cases/ pop at risk

Prevalence ~ incidence rate x average disease duration
Prevalence > incidence for chornic dz

Question 9

Odds ratio (OR)

Answer 9

Used in case controlled (obs/retro)

dz expos/dz unexpo)/(healthy expo/healthy unexpo

Question 10

Relative risk (RR)

Answer 10

Used in cohort (obs/retro or pros)
(dz/all exposed)/(dz/all unexposed)
If prevalence low, RR~OR

Question 11

Attributable risk

Answer 11

Diff in risk btwn exposed and unexposed
If lung cancer risk 21% in exposed, 1% in unexposed,
then 20% is ATTRIBUTABLE RISK to smoking

*1/AR= number needed to be exposed (for 1 pt to be harmed)

Question 12

Absolute risk reduction (ARR)

Answer 12

Absolute reduction in risk due to tx compared to control
8% of placebo vs. 2% vaccinated develop flu = 6%

*1/ARR= number needed to treat (for 1 pt to benefit)

Question 13

Precision vs. accuracy

Answer 13

Precision: consistent and reproducible/reliable, absence f random variation in the test
High precision=> low SD

Accuracy: trueness of test measure, validity, absences of systematic erros or bias in a test

Question 14

Biases…

Answer 14

Selection: non random assignment (loss to f/u)

Recall: knowledge of presence of disorder alters recall by subjects; common in RETROSPECTIVES.

Sampling: subjects not generalizable to population

Late-look bias: info gathered at an inappropriate time (using a survey to study fatal dz, but only those alive will be able to answer the survey)

Procedure bias: subjects not treated the same; more attention given to tx group, so better adherence)

Confounding bias: occurs when factor is related to both exposure and outcome, distorting the effect of exposure

Lead-time bias: early detection confused with increased survival, seen with improved screening, but natural hx of dx is not changed, but early detection makes it seem AS THOUGH survival has increased

Observer-expectancy effect: researcher’s belief in the efficacy of a tx changes the outcome of the tx

Hawthorne effect: the group being studying changes its behavior due to the knowledge of being studied. Dr. Hawthorne is watching you.

Question 15

Normal distribution

Answer 15

Gaussian, aka bell-shaped
Mean=median=mode

Mode is least affected by outliers

Positive skew: means>median>mode, longer tail on right
Negative skew: mean<mode, longer tail on left

Question 16

SD and SEM

Answer 16

N= sample size, SD
SEM= SD/square rt(n)
SEM decreases as n increases

Question 17

Statistical errors types

Answer 17

Type 1 error (alpha): mistakenly stating the existence of difference. (false positive) alpha is the probability of making a type I error.
If P

Power (1 - beta): the likelihood of finding a difference if one in fact exists. It increases with HIGH sample size, HIGH expected effect sized, HIGH precision of measurement.

Question 18

Meta analysis

Answer 18

Pools data and integrates results from several similar studies to reach an overall conclusion, increases statistical power.

Limitation: quality of individual studies or bias in study selection.

Question 19

Confidence interval

Answer 19

Range of values in which a specified prob of the means of repeated samples would be expecteed to fall
Cl= range from (mean+/-Z(SEM))

For 95% CI, Z =1.96
For 99% CI, Z=2.58

Null hypothesis not rejected if:

• 95% CI for a mean difference between two variables include 0.
• 95% CI for OR or RR includes 1

If the CIs between two groups do NOT overlap, significant difference exists. If DO overlap, no difference.

Question 20

T test vs. ANOVA vs. X2

Answer 20

T test: diff btw the MEANS of 2 groups = Mr T is MEAN

ANOVA: diff btw the MEANS of 3 groups or more
ANalysis Of VAriance of 3 or more group

Chi Square: test checks difference between 2 or more % or proportions of categorical outcomes (not mean values)

Question 21

Pearson’s correlation coefficient (r)

Answer 21

r is always between -1 and +1, the closer the absolute value of r is to 1, the stronger the linear correlation between the two variables.
Coefficient of determination = R^2, value that is usually reported.

Question 22

Dz prevention

Answer 22

1’ prevent disease occurrence, HPV vaccination
2’ early detection, PAP smear
3’ reduce disability from dz, chemo

PDR: prevent, detect, reduce disability

Question 23

Medicare and Medicaid

Answer 23

MedicarE is for elderly, >= 65 yrs, =<65 with cercetain disability, or those with ESRD

MedicaiD for Destitute

Both are federal programs, originated from amendments to the social security act.

MedicaiD is joint federal AND state health assistance for people with very low income.

Question 24

Core ethical principles

Answer 24

1) Pt autonomy: obligation to respect pts as individuals and to honor their preferences in medical care
2) Beneficence: physicians have a special ethical duty to act in the pts’ best interest. May conflict with autonomy. If the pt CAN make an informed decision, ultimately, the pt has the right.
3) Nonmaleficence: do no harm. However, if the benefit of an intervention outweigh the risks, a pt may make an informed decision to proceed (most surgeries and medications fall into this categories).
4) Justice: to treat persons fairly.

Question 25

Informed consent

Answer 25

Legally requires discussion of pertinent info, pts’ voluntary agreement to the plan of care, freedom from coercion.

Exceptions when pts lacking decision making capacity or is legally incompetent, implied consent in an emergency, therapeutic privilege (withholding info when disclosure would severely harm the pt or undermined informed decision making capacity), pts waiving the right of informed consent.

Pts must have an intelligent understanding of the risk, benefits, and alternatives including no intervention. Written consents can be revoked by the pts at any time, even orally.

Question 26

Consents for minors

Answer 26

A minor is generally any person <18 yrs of age.
Parental consent law vary from state to state.

Generally, consent must be obtained unless minor is emancipated (e.g. married, self-supporting, has children, or in military).

Parental consent NOT required in (1) emergencies, (2) prescribing contraceptives, (3) treating STDs, (4) medical care of pregnancy, and (5) treatment of drug addiction

Question 27

Decision making capacity

Answer 27

Physicians must determine whether psychologically and legally capable of making a decision.

Components: decision must be consistent with pts values and goals, not clouded by a mood disorder, delusion, hallucination.

The pts family cannot require doctors to withhold info from the pt if pt demonstrates decision making capacity.

Question 28

Advanced directives

Answer 28

Oral advance directives: problems arise from variance in interpretation.

Living will (written advance directive): describes treatment the pt wishes to receive or not receive if incapacitated.

Medical power of attorney: pts designates an agent to make medical decision in the event that he/she loses decision-making capacity. Pt may also specify decision in clinical situation. Pt can revoke anytime pt wishes. More flexible than a living will.

Priority of surrogates: spouse, adult children, parents, adult sibling, other relatives.

Question 29

Confidentiality

Answer 29

Respect pt privacy and autonomy. If pts incapacitated, disclosing information to fam and friends guided by professional judgment of pts’ best interest.

Exceptions: potential to harm others, self-harm so great, no alternative means to warn or protect those at risk, physicians can take steps to prevent harm.

Examples of exceptions: reportable diseases (STD, TB, hepatitis, food poisoning), the Tarasoff decision (CA Supreme Court requiring physicians to inform potential victims from harm), child and/or elder abuse, impaired automobile drivers, and SI/HI pts.

Question 30

Ethical situations

Answer 30

A child wanting to know about his/her condition: ask what the parents have told. The parents decide what info can be relayed about the illness.

17 yo girl pregnant and requests an abortion: many states require parental notification or conset for minors for abortion. Unless at medical risk, do not advice an abortion regardless of her age of the condition of the fetus.

15 yo girl pregnant and wants to keep the child, but parents want adoption: the pt retains the right to make decisions regarding her child, even if parents disagree. Provide info about practical issues of caring for a baby.

No physician assisted suicide, but may prescribe medically appropriate analgesics that coincidentally shorten the pt’s life.