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sensitivity =

=TP/(TP + FN)
*sensitivity rules OUT


specificity =

=TN/(TN + FP)
*specificity rules IN


Positive Predictive Value = PPV =

= TP/(TP + FP)

*PPV = proportion of test results that are true positive
*if increased prevalence, then increased PPV


Negative Predictive Value = NPV =

= TN/(TN+FN)

*proportion of negative test results that are truly negative
*increased prevalence, decreased NPV


Point prevalence =

=total cases in population at a given time/total population at a given time


Prevalence =

=incidence X disease duration


Incidence =

=new cases in popl over a given period of time/total popl at risk during that time period


Odds Ratio = OR =

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

*use OR for case-control studies


Relative Risk = RR=

= [a/(a+b)]/[c/(c+d)]

*use RR for cohort studies


Attributable Risk =

= [a/(a+b)] - [c/(c+d)]

*AR is the proportion of disease occurences attributable to exposure to a risk factor


Absolute Risk Reduction

the reduction in risk associated with a treatment as compared to a placebo


Number needed to treat = NNT =

= 1/absolute risk reduction

= 1/[a/(a+b)]


Number needed to harm = NNH =

= 1/attributable risk


Precision, Accuracy, Reliability, Validity, Random error, Systemic error

Precision = Reliability
Accuracy = Validity

Random error - reduces precision in a test
Systemic error - reduces accuracy in a test


Standard error of the mean = SEM =

=σ/sqrt of n

used in Normal/Guassian/Bell-Shaped curves (where mean = mode = median)

σ = standard deviation
sqrt of n = square root of sample size

*note: SEM decreases as n (sample size) increases


In a normal/gaussian/bell-curve (where mean=median=mode), what percent of the population is 1 σ (standard deviation) to either side of mean? 2σ to either side of mean? 3σ on either side of mean?

What percent of the population correlates wtih a σ = 1.645 on either side of the mean?

1σ on either side of mean = 68% of popl
2σ = 95%
3σ = 100% (99.7%)
1.645σ = 90% of popl


relationship of mean, median,mode in a positively-skewed statistical distribution?

positive skew: asymmetry with tail on the right
mean > median > mode


relationship of mean, median,mode in a negatively skewed statistical distribution

negative skew - asymmetry with tail on left

mean < median < mode


Null hypothesis = H0 =

hypothesis of no difference; there's no association between disease and the risk factor in the population


Alternative hypothesis = H1

hypothesis that there is some difference; there is some association between the disease and the risk factor in the population


type 1/alpha error = false positive error

stating there is an effect or difference when none exists; accepting H1 (rejecting H0) when H0 is really true

*ie convicting an innocent man


p value

p = probablity of making a type 1 (alpha) error
ps not actually there)


Type 2/Beta error = False negative error

stating there is not an effect or difference when one exists; not rejecting H0 when it actually is false (so choosing H0 when H1 is true)

*ie setting a guilty man free



probability of making a type 2 (beta) error


Power =

= 1 - Beta

probability of rejecting H0 when it is in fact false or likelihood of finding a difference when one in fact exists

if increase sample size, then increase power (power in #s!)


Meta analysis

pools data/results from several similar studies to reach an overall conclusion; increases power


Confidence Interval = CI =

Range from [mean - Z(SEM)] to [mean + Z(SEM)]

*example, for a 95% CI:
= mean +/- 1.96 X SEM
= mean +/- 1.96 X (σ/sqrt n)

*if 95% CI for a mean difference between 2 variable includes 0, then there's no significan different and H0 is not rejected
*if 95% CI for odds ratio or relative risk includes 1, H0 is not rejected


CI 90%, Z = ?
CI 95%, Z = ?
CI 99%, Z = ?

CI 90%, Z = 1.645
CI 95%, Z = 1.96
CI 99%, Z = 2.58

*95% CI, corresponds to p=0.05


t-test vs ANOVA vs chi^2

t-test --> checks difference between means of 2 groups

ANOVA --> checks difference between means of 3 or more groups

chi-square test --> checks the difference between 2 or more percentages or proportions of categorical outcomes (not of mean values)


correlation coefficient = r:

r is always between -1 and 1; the closer the absolute value of r is to 1, the stronger the correlation between the 2 variables

*usually report r^2 = coefficient of determination


Medicare vs Medicaid:

Medicare: pts > 65 years old ( e for elderly), <65 with certain disabilities, and pts with ESRD

Medicaid: federal and state healt assistance for people with very low income (d for destitute)


core ethical principles: autonomy, beneficence, nonmaleficence, justice

autonomy - must respect patients as individuals and honor their preferences in medical care

beneficence - physicians must act in patients' best interest; may conflict with autonomy. if pt can make an informed decision, then pt ultimatley has right to decide

nonmaleficence - "do no harm"; but, if benefits of an intervention outweigh risks, pt may make informed decision to proceed (ie with surgeries, meds...)

justice - treat persons fairly


Exceptions to informed consent:

1) Pt lacks decision-making capacity or is legally incompetent (ie minors)
2) Implied consent in an emergency
3) Therapeutic privilege - withholding information when disclosure would severely harm pt or undermind informed decision-making capacity
4) Waiver - pt waives right of informed consent


Minors: Exceptions for when parental consent is NOT required:

-pt is married, self-supporting, has kids, is in military
-emergency situations
-treatment involving STDs, medical care during pregnancy, managing drug addiction


Advance directives:
-Living will
-Durable power of attorney

*oral advance directive - use incapacitated pt's prior oral statements as a guide; more valide if pt was informed, directive was specific, pt made a choice; decision was repeated over time to multiple people

*living will = written advance directive - written by pt ahead of time, in case he/she become incapacitated and cannot communicate

*durable power of attorney - pt designates a surrogate to make medical decisions in case he/she loses decision-making capacity; surrogate retains power unless revoked by a patient; more flexible than a living will


Can a pt's family require a doctor to withhold information from the pt?



Priority of surrogates, if a patient becomes incompetent, but did not prepare an advance directive:

spouse > adult children > parents > siblings > other relatives


Exceptions to confidentiality:

-potential harm to others is serious
-likelihood of harm to self is great
-no alternative means exist to warn or to protect those at risk
-physicians can take steps to prevent harm:

1) reportable disease - physicians my have to warn public officials and identifiable people at risk
2) Tarasoff decision - law requiring physician to directly inform and protect potential victrim from harm; may involve breach of confidentiality
3) child and/or elder abuse (obligated to report SUSPICION)
4) impaired automobile drivers
5) suicidal/homicidal pts


What are considered "reportable diseases" (which may be exceptions to confidentiality)

1) STDs: AIDS, gonorrhea, syphilis (sometimes chlamydia, depends on state)
2) Hepatitis
3) Child immunization infections: MMR and chickenpox
4) Food poisoning: shigella, salmonella
5) TB


What do you do if a 17 year old girl is pregnant and requests an abortion?

many states require parental notification or consent for minors for an abortion; UNLESS SHE IS AT MEDICAL RISK, do not advise a patient to have an abortion regardless of her age or the condition of the fetus


what to do if a patient is suicidal?

assess the seriousness of the threat; if serious, suggest that the patient voluntarily remain in the hospital; a patient can be hospitalized involuntarily if he/she refuses.


Apgar score

= assessment of newborn health via a 10-point scale; evaluated at 1 minute and 5 minutes post-birth
*based on:


*> or = to 7 - good
*4-6 - assist and stimulate
*<4 at later time points, then risk that child will develop long-term neuro damage


Definition of low birth weight?

<2500 g

*associated with increased physical and emotional problems
*caused by prematurity or intrauterine growth retardation
*complications: infections, RDS, necrotizing enterocolitis (if feed neonate with formula too soon), intraventricular hemorrhage, and persistent fetal circulation (PDA, PFO...)


Berkson's bias

a type of selection bias; studies on hospitalized patients


selection bias

nonrandom assignment to study group (ie berkson's bias; loss to follow-up)


recall bias

knowledge of presence of disorder alters recall by subjects


sampling bias

subjects are not representative relative to general population; so, results are not generalizable


late-look bias

information gathered at an inappropriate time; a type of recall bias
-ie using a suvery to study a fatal disease (b/c only pts still alive can answer the survey...)


procedure bias

subjects in different groups are not treated the same - ie pay more attention to treatment group, stimulating greater compliance


confoundibg bias

occurs with 2 closely associated factors; the effect of 1 factor distorts or confuses the effect of the other


lead-time bias

early detection confused with increased survival; seen with imporved screening (the natural history of the disease is not changed; but, early detection makes it seem as though survival has increased)


Pygmalion effect

when a researcher's belief in the efficacy of a treatment changes the outcome of that treatment


Hawthorne effect

when a group being studied changes its behavior owing to the knowledge being studied


How to reduce bias:

1) Blind studies
2) Placebos
3) Crossover studies (ie each subject is at some point on placebo and some point on drug; so each subject acts as own control to limit confounding bias)
4) Randomizaton to limit selection bias and confounding bias


At what age does the moro reflex disappear?

between birth and 3 mos


when does a child begin to have stranger anxiety?
separation anxiety?

stranger anxiety: 7-9 mos
separation anxiety: 12-15 mos


when does a child begin to climb stairs?

12-24 months


block stacking milestones in child development?

-stacks 3 blocks at 1 year
-stacks 6 blocks at 2 years


when can a child begin feeding self with a fork and spoon?

24-26 months


when may a child kick a ball?

24-36 months


toilet training age?

24-36 months (pee at three!)


tricycle riding age?

3 years (3-cycle at 3!)


gender identity development age?

24-36 months


buttons and zippers, brushes teeth, hops on 1 foot, makes stick figure drawings?

4 years old


imaginary friends age?

4 years old


copies line or circle drawings - development age?

3 years old


Changes in the elderly: (sex, sleep, suicide, vision, hearing, immune, bladder, renal, pulmonary, GI, muscle mass, fat)

1) Sex: (note: sex interest does not change)
-Men--> slower erection/ejaculation, longer refractory period
-Women --> vaginal shortening,thinning, dryness
2) Sleep:
-decreased REM, slow-wave sleep (stages 3 and 4)
-increased latency and awakenings (takes longer to reach REM sleep)
3) increased suicide rate (males 65-74 yo have highest suicide rate in US)
4) decreased vision, hearing, immune response, bladder control
5) decreased renal, pulmonary, GI function
6) decreased muscle mass, increased fat

*Note: 5 and 6 affect drug dosage and metabolism; for this reason, start SLOW and LOW when giving drugs to elderly!


Normal bereavement vs Pathologic grief

Normal bereavement: shock, denial, guilt, somatic symptoms; can last up to 2 months; may experience illusions

Pathologic grief: excessively intense grief, grief that lasts >2 months; or grief that is delayed, inhibited or denied. May have depressive symptoms, delusions, hallucinations.


Physiologic effects of stress:

stress induces production of:
-free fatty acids
-17-OH corticosteroids (increased corticosteroids --> immunosuppression)
-also, affects: water absorption (have decreased water absorption), muscular tonicity, gastrocolic reflex, and mucosal circulation


How to calculate BMI?
What BMI range = overweight?

BMI = weight in kg/(height in meters)^2

Overweight: 25.0-29.9
Obese: >30
morbidly obese: >40


Drugs, Diseases, and Psychological issues that may lead to sexual dysfunction:

Drugs: antihypertensives, esp Beta-blockers; neuroleptics; SSRIs; ethanol
Dieases: depression, diabetes, atherosclerosis (because decreased blood flow to area), hyperprolactinemia, low testosterone
Psychological: Performance anxiety


only serotonin-releasing neurons in CNS?

Raphe nucleus


Which stage of sleep do we spend most of the time in?

Stage 2


EEG waveform patterns during each sleep stage:

"at night, BATS Drink Blood"
*awake (eyes open) --> Beta waves (highest frequency, lowest amplitude)
*awake (eyes closed) --> Alpha waves
*stage 1 --> Theta waves
*stage 2 --> Sleep spindles and K complexes
*stage 3 --> Delta waves (lowest frequency, highest amplitude)
*REM --> Beta waves


During which sleep stage does one have sleep spindles and K complexes on EEG?

Stage 2 sleep


What is the key to initiating sleep?

Serotonergic predominance of the raphe nucleus


What drug can be used to treat enuresis (bed-wetting) and why?

Imipramine, because it decreases stage 3 sleep (when bed-wetting occurs)


During what sleep stage does teeth grinding (bruxism) occur?

Stage 2 (deeper sleep, when have sleep spindles and K complexes on EEG)


During what sleep stages may one experience sleepwalking, night terrors, or bed-wetting?

Stage 3 sleep (deepest, non-REM sleep; slow-wave sleep; have delta waves on EEG)


During what sleep stage does one experience: dreaming, loss of motor tone, memory processing, erections, increased brain oxygen use?

REM sleep; Beta waves on EEG


Alcohol, Benzos, and Barbiturates do what to sleep stages?

Reduced REM and delta (stage 3) sleep


What drug may be useful to treat night terrors and sleepwalking and why?

Benzos; because decrease stage 3 sleep, during which sleepwalking and night-terrors occur


What is the principal neurotransmitter in REM sleep?



How does NE affect REM sleep?

NE reduces REM sleep


How often does REM sleep occur?

Every 90 minutes; increased duration as go through the night


Pulse, BP, eye activity, and penile/clitoral tumescence (swollen-ness) during REM sleep:

-increased and variable pulse and BP
-extraocular movements during REM sleep d/t PPRF activity (REM = Rapid eye movements; mediated by PPRF)
-Penile/Clitoral tumescence

"REM sleep is like sex: increased pulse, penile/clitoral tumescence, decreases with age)


Why is REM sleep also called "paradoxical sleep" or "desynchronized sleep"?

Because it has the same EEG pattern as wakefulness (Beta waves)


What mediates the rapid eye movements of REM sleep?

PPRF (paramedian pontine reticular formation/conjugate gaze center)


How do sleep patterns change in depressed patients?

-decreased slow-wave sleep (stage 3)
-decreased REM latency (so, get to REM quicker!)
-increased REM early in sleep cycle
-increased total REM sleep
-repeated nighttime awakenings
-early-morning awakenings


Hypnagogic vs Hypnopompic hallucinations?

Hypnagogoic = just before sleep
Hypnopompic = just before awakening

*pts wtih narcolepsy may have these hallucinations


-what is it?
-main presentation?

-disordered regulation of sleep-wake cycles
-pts are very tired during day
-may have hypnogogic or hynopompic hallucinations
-nocturnal and narcoleptic sleep episodes start off with REM sleep
-Cataplexy in some pts
-Genetic component
-Treat with stimulants (amphetamines, modafinil) and sodium oxygbate



-loss of all muscle tone following a strong emotional stimulus, ie laughter
-seen in some pts with narcolepsy


What controls the circadian rhythm?

SCN (suprachiasmatic nucleus) of the hypothalamus drives the circadian rhythm; controls ACTH, prolactin, melatonin, nocturnal NE release

*Retina stimulates SCN --> NE release --> Pineal gland --> Melatonin

*So, SCN is regulated by the environment (light); so retina stimulates SCN


Kubler-Ross Grief Stages

(may not occur in this order)
1) Denial
2) Anger
3) Bargaining
4) Grieving
5) Acceptance