Cross-sectional study (observational) design
collects data from a group of people to assess frequency of disease at a particular point in time
(asks what is happening)
Measures of a cross-sectional study
- disease prevalence
- can show risk factor association with disease, but does not establish causality
Case-control study (observational/retrospective) design
compares a group of people with disease to a group without disease; looks for prior exposure or risk factor
(asks what happened)
Measures of a case-control study
Cohort study (observational/prospective or retrospective) design
compares a group with a given exporsure or risk factor to a group without such exposure; looks to see if exposure increases the likelihood of disease
(prospective - asks who will develop disease)
(retrospective - asks who has developed the disease)
Meausres of a cohort study
Twin concordance study design
compares the frequency with which both monozygotic twins or both dizygotic twins develop the same disease
Meausres of a twin concordance study
heritability and influence of environmental factors
Adoption study design
compares siblings raised by biological vs adoptive parents
Measures of an adoption study
heritability and influence of environmental factors
A clinical trial is an experimental study involving humans that compares…
the therapeutic benefits of 2 or more treatments, or of treatment and placebo.
Study quality of a clinical trial is improved when the study is…
randomized, controlled and double-blinded.
Triple-blind refers to the…
additional blinding ofo the researchers analyzing the data.
Phase I Trial
- small number of healthy volunteers
- “Is it safe?”
- Assesses safety, toxicity and pharmacokinetics
Phase II Trial
- small number of patients with disease of interest
- “does it work?”
- Assesses treatment efficacy, optimal dosing, and adverse effects.
Phase III Trial
- large number of pts randomly assigned either to the treatment under investigationor to the best available treatment/placebo
- asks “is it as good or better?”
- compares new treatment to current standard of care
Phase IV Trial
- posmarketing surveillance trial of pts after approval
- “can it stay?”
- detects rare or long term effects
Sensitivity is the…
proportion of all people with a disease who test positive or the probability that a test detects disease when it is present. (true-positive rate)
A sensitivity value approaching 100% is desirable for…
ruling out disease and indicates a low-false negative rate.
High sensitivity tests should be used for screening in diseases with..
Specificity is the…
proportion of all people without disease who test negative or the probability that a test indicates non-disease when disease is absent. (true-negative rate)
Specificity value approaching 100% is desirable for…
ruling in disease and indicates a low false-positive rate.
High specificity tests should be used for…
confirmation after a positive screening test.
TN/(TN + FP)
Positive Predictive Value (PPV) is the…
proportion of positive test results that are true positive. The probability that a person actually has the disease given a positive test result.
TP/(TP + FP)
directly with prevalence or pretest probability. A high pretest probability leads to a high PPV.
Negative Predictive Value (NPV) is the…
proportion of negative test results that are true negative. The probability that a person is actually disease free given a negative test result.
TN/(FN + TN)
inversely with prevalence or pretest probability. A high pretest probability give a low NPV.
(number of new cases in a specified time period)/(population at risk during the same time period)
(number of existing cases)/(population at risk)
Prevalence is about equal to…
the incidence rate x avg disease duration.
Prevalence is greater than incidence for…
The odds ratio is the…
odds that the group with the disease was exposed to a risk factor (a/c) divided by the odds that the group without disease was exposed (b/d).
Odds Ratio (OR) =
Relative risk is the risk of…
developing disease in the exposed group divided by the risk in the unexposed group.
If prevalence is low, the RR is about equal to…
Relative Risk (RR) =
Relative risk reduction is the…
proportion of risk reduction attributable ot the intervention as compared to a control. RRR = 1 - RR
Attributable risk is the…
difference in risk between exposed and unexposed groups or the proportion of disease occurences that are attributable to the exposure.
Attributable risk =
[a/(a+b)] - [c/(c+d)]
Absolute risk reduction (ARR) is the…
difference in risk attributable to the intervention as compared to a control.
The number needed to treat is the…
number of pts who need to be treated for 1 pt to benefit. Calculated as 1/ARR.
Number needed to harm is the…
number of pts who need to be exposed to a risk factor for 1 pt to be harmed. Calculated as 1/AR.
Precision is the…
consistency and reproducibility of a test (reliability). The absence of random variation.
Increased precision decreases…
the standard deviation.
Accuracy is the…
trueness of test measurements (validity). The absence of systematic error or bias.
Selection bias is…
nonrandom assignment to participat in a sudy group. Most commonly a sampling bias.
Examples of Selection bias include:
- Berson bias (a study looking only at inpatients)
- Loss to follow-up (studying a disease with early mortality)
- Healthy worker and volunteer bias (study populations are healthier than the general population)
Strategies to reduce selection bias
- ensure the choice of the rigth comparison group
Recall bias is…
awareness of disorder alters recall by subjects; common in retrospective studyies.
(ex. pts with disease recall exposure after learning of similar cases)
Strategy to decrease recall bias
decrease time from exposure to follow-up
Measurement bias is…
information is gathered in a way that distorts it.
Ex. Hawthorne effect - groups who know they’re being studied behave differently than they would otherwise
Strategy to decrease measurement bias
use of placebo control groups with blinding to reduce influence of participants and researchers on experimental procedures and interpretation of outcomes
Procedure bias is when…
subjects in different groups are not treated the same.
Ex. pts in treatment group spend more time in highly specialized hospital units
researcher’s belief in the efficacy of a treatment changes the outcome of that treatment
(ex. if an observer expects the treatment group to show signs of recovery, then he is more likely to document positive outcomes)
Confounding bias is when…
a factor is related to both the exposure and outcome but not on the causal pathway and this leads to the factor distorting or confusin gthe effect of exposure on outcome.
Ex. of Confounding bias
Pulmonary disease is more common in coal workers than the general population; however, people who work in coal mines also smoke more frequently than the general population.
Strategies to reduce confounding bias
- multiple/repeated studies
- crossover studies (subjects act as their own control)-matching (pts with similar characteristics in both treatment and control groups)
Lead-time bias is when…
early detection is confused with increased survival; seen with improved screeing techniques
Ex. early detection makes it seem as though survival has increased, but the natural history of the disease has not changed.
Strategies to reduce lead-time bias
-measure “back-end” survival (adjust survival according to the serverity of the disease at the time of diagnosis)
(sum of values)/(total number of values)
middle value of a list of data sorted from least to greatest
most common value
Standard deviation =
how much variability exists from the mean in a set of values
Standard error of the mean =
an estimation of how much variability exists between the sample mean and the true population
SEM = standard deviation/(square root of the sample size)
mean = median = mode
Bimodal distribution suggests…
2 different populations (ex. metabolic polymorphism such as fast vs. slow acetylators; suicide rate by age)
- typically mean > median > mode
- asymmetry with longer tail on the right
- typicall, mean < median < mode
- asymmetry with longer tail on the left
Null hypothesis is a…
hypothesis of no difference.
ex. there is no association between teh disease and risk factor in the population
Alternative hypothesis is a…
hypothesis of some difference.
Ex. there is some association between the diseae and the risk factor in the population
- Stating that there is a difference/effect when one exists (null hypothesis is rejected in favor of the alternative hypothesis)
- stating that ther is not an effect/difference when none exists (null hypothesis not rejected)
Type I error (alpha)
stating that there is an effect or difference when non exists (null hypothesis incorrectly rejected); aka false-positive
Alpha is the probability of…
making a type I error. If p < .05, then there is less than a 5% chance that the data will show something that is not really there.
Type II erro (beta)
stating thatthere is not an effect or difference when one exists (null hypothesis is not rejected when it is false); false-negative error
Beta is the probability of…
making a type II error. It is related to statistical power (1-beta), which is the probability of rejecting the null hypothesis when it is false.
Power is increased and beta is decreased by:
- increased sample size
- increased expected effect size
- increased precision of measurement
pools data and integrates results from several similar studies to reach an overall conclusion. It increases statistical power.
Meta-analysis is limited by…
quality of individual studies or bias in study selection.
Confidence interval is…
the range of values in which a specified probability of the means of repeated samples would be expected to fall.
Confidence Interval =
from [mean - Z(SEM)] to [mean + Z(SEM)]
For the 95% CI, Z=
If the 95% CI for a mean difference between 2 variables includes 0, then there is…
no significant difference and null hypothesis is not rejected.
If the 95% CI for odds ratio or relative risk includes 1, then…
null hypothesis is not rejected.
If the CIs between 2 groups do not overlap, then…
a significant differnece exists.
A t-test checks…
the differences between means of 2 groups.
Ex. comparing the mean bp between men and women
differences between means of 3 or more groups.
Ex. comparing the mean blood pressure between members of 3 different ethnic groups
Chi-square test checks…
differenc between 2 or more percentages or proportions of categorical outcomes
Ex. comparing the percentage of members of 3 different ethnic groups who have essential HTN
r is the pearson correlation coefficient which is always between…
-1 and +1. The closer the absolute value of r is to 1, the stronger the linear correlation between the 2 variables.
A positive r means a…
positive correlation and a negative r value means a negative correlation.
r^2 is the…
coefficient of determination.
prevents disease occurrence (ex. HPV vaccination)
screening early for disease (ex. PAP smear)
treatment to reduce disability from disease (ex. chemo)
identifying pts at risk of unnecessary treatment, protecting from the harm of new interventions
Medicare is available to…
patients 65 and older and some with certain disabilities less than 65 and those with ESRD.
joint federal and state health assistance for people with very low income.
Respecting pt autonomy is the obligation to…
respect pts as individuals (leading to truth telling and confidentiality), to create conditions necessary for autonomous choice (informed consent), and to honor their preferene in accepting or not accepting medical care.
Physicians have a special ehtical duty to act in the patient’s best interest. This may conflic with autonomy or what is best for society.
“Do no harm.” - must be balanced against beneficence; if the benefits outweight the risks, a pt may make an inforemed decision to proceed
Justice is to…
treat persons fairly and equitably. This does not always imply equally (ex. triage).
Informed consent is a process that legally requires…
disclosure, understanding, mental capacity and voluntariness.
the ability to comprehend whereas mental capcity is a legal determination.
Exceptions to informed consent (4):
- pt lacks decision making-capcaity or is legally incompetent
- implied consent in an emergency
- therapeutic privelage (withholding information when disclosure would severely harm the pt or undermine informed decision making capacity)
- waiver (pt explicitly waives the right of informed consent)
In general parental consent should be obtained for minors (<18) unless the minor is…
legally emancipated (ex. married, self-supporting, or in the military).
Situations in which parental consent is usually not required:
Sex (contraception, STDs, pregnancy)
Rock and Roll (emergency, trauma)
Decision-making capacity components (6)
- patient is 18 or older (or legally emancipated)
- pt makes and communicates a choice
- pt is informed (knows and understands)
- decision remains stable over time
- decision is consistent w/ pts values and goals, not clouded by a mood disorder
- decision is not a result of delusions or hallucinations
A medical power of attorney may be revoked….
anytime the pt wishes (regardless of their competence).
more flexible than a living will
Priority of surrogates:
spouse, adult children, parents, adult siblings, other relatives
General principles to exceptions to confidentiality:
- potential physical harm to others is serious and imminent
- likelihood of harm to self is great
- no alternative means exist to warn or protect those at risk
- physician can take steps to prevent the harm
Examples of exceptions to pt confidentiality
- reportable diseases (STDs, TB, heptitis, food poisoning)
- Tarasoff decision (California supreme court decision requiring physician to directly inform and protect potential victim from harm)
- child and/or elder abuse
- impaired automobile drives (epileptics)
- suicidal/homicidal pts
Response to a patient who is not adherent
Attempt to identify the reason for nonadherence and determine his/her willingness to change; do not coerce the pt into adhering or refer him/her to another physician.
Response to a patient who desires an unnecessary procedure:
Attempt to understand why the pt wants the procedure and address underlying concerns; do not refuse to see the pt or refer him to another physician; avoid performing unnecessary procedures
Response to a patient who has difficulty taking meds
Provide written instructions; attempt to simplify treatment regimens; use teach-back method to ensure pt comprehension
Response to family members who ask for info about pt prognosis
avoid discussing issues w/ relatives w/o pt permission
Response to a pt’s family member who asks you not to disclose the results of a test if the prognosis is poor bc the pt will be “unable to handle it”
Attempt to identify why the family member believes this and explain that as long ast the pt has decision-making capacity and does not indicate otherwise, communication of info concerning his/her care will not be withheld
Response to a child who wishes to know more about their illness
ask what the parents have told the child about the illness; parents of a child decide what info can be relayed
Response to a 17 yr old pregnant girl who 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 pt to have an abortion regardless of her age or the condition of the fetus.
Response to a 15 yr old girl who is pregnant and wants to keep the child; the parent want you to tell her to give it up for adoption
the pt retains the right to make decisions regarding her child, even if her parents disagree; provide info to the teenager about the practical issues of caring for a baby; discuss the options, if requested. Encourage discussion between the teenager and her parents to reach the best decision
Response to a terminally ill pt who requests physician assistance in ending own life
in the overwhelming majority of states, refuse involement in any form of physician-assisted suicide. Physicians may, however, prescribe medically appropriate analgeiscs that coincidentally shorten the pts life.
Response to a suicidal pt
assess the seriousness of the threat; if it is serious, suggest that the pt remain in the hospital voluntarily; if they refuse, involuntarily hospitalize them
Response to a pt who finds you attractive
ask direct, closed-ended questions and use a chaperone if necessary; romantic relationships are never appropriate; Never say “there can be no relationship while you are a pt” because this implies that a relationshhip may be possible if the individual is no longer a pt
A woman who had a mastectomy says she now feels “ugly:. Response:
find out why the pt feels this way; do not offer falsely reassuring statements (“you still look good”)
Patient is angry about the amount of time he/she spent waiting in the waiting room. Response:
Acknowledge the pt’s anger but do not take a pt’s anger personally. Apologize for any inconvenience. Stay away from efforts to explain the delay.
Patient is upset witht he way he/she was treated by another doctor. Response:
suggest that the patient speak directly to that physician regarding his/her concerns. If the problem is with a member of the office staff, tell the pt you will speak to that person.
A drug company offers a “referral fee” for every pt a physician enrolls in a study. Response:
Eligible pts who may benfit from the study may be enrolled but it is never acceptable for a physician to receive compensation from a drug company. Pts must be told about the existence of a referral fee.
A physician orders an invasive test for the wrong pt. Response:
No matter how serious or trivial a medical error, a physician is ethically obligated to inform a pt that a mistake has been made.
A pt requires a treatment not covered by his/her insurance. Response:
Never limit or deny care because of the expense in time or money. Discuss all treatment options with pts, even if some are not covered by their insurance.
APGAR is assessed at..
1 minute and 5 minutes.
APGAR is based on:
Appearance Pulse Grimace Activity Respiration
(7 or more is good, 4-6 assist and stimulate, less than 4 resuscitate)
Low birth weight is defined as…
< 2500 grams.
Low birth weight is caused by…
prematurity or intrauterine growth retardation (IUGR).
Low birth weight is associated with increased risk of…
SIDS and overall increased mortality.
Other problems of low birth weight include…
imparied thermoregulation, immune fxn, hypoglycemia, polycythemia, impaired neurological/emotional development.
Complications of low birth weight include…
infxns, RDS, necrotizing enterocolitis, intraventricular hemorrhage, and persistent fetal circulation.
Motor 0-12 months
- Primitive reflexes disappear
- Picks (passes toys hand to hand at 6 mo and pincer grasp by 10 mo)
- points to objects by 12 months
Moro reflex disappears by…
3 months (startle reflex)
Rooting disappears by…
4 months (cheek stroke)
Palmar reflex disappers by…
Babinski reflex disappears by…
Lifts head up prone by…
Rolls and sits by…
Social milestones of the infant (0-12 months)
- social smile (by 2 months)
- stranger anxiety (by 6 months)
- separation anxiety (by 9 months)
Verbal/Cognitive Milestones of the Infant
- orients (to voice by 4 months and to name/gestures by 9 months)
- object pemanence (by 9 months)
- oratory (says mama and dada by 10 months)
Motor milestones of the toddler (`12-36 months)
- climbs stairs (18 mo)
- cubes stacked (3 by 3 yrs)
- cultured (feeds self with fork and spoon by 20 mo)
- kicks ball (by 24 mo)
Social milestones of the toddler
- recreation (parallel play by 12 mo)
- rapprochement (moves away and returns to mother by 24 mo)
- realization (core gender identity by 36 mo)
Verbal/cognitive milestones of the toddler
200 words by age 2
2 word sentences
Motor milestones of the preschool child (3-5)
- rides tricycle
- copies line or circle
- stick figure by 4 yrs
- hops on one foot by 4
- uses button or zippers, grooms self (by 5)
Social milestones of the preschool child
- comfortably spends part of the day away from the mother (by 3)
- cooperative play, has imaginary friends (by 4)
Verbal/cognitive milestones of the preschool child
- 1000 words by age 3
- uses complete sentences and prepositions by 4
- tells detailed stories by 4
Sexual changes in older men
- slower erection/ejaculation
- longer refractory period
Sexual changes in older women
-vaginal shortening, thinning and dryness
Sleep changes in the elderly
- decreased REM and slow-wave sleep (stages 3/4)
- increased sleep onset latency
- increased early awakenings
Other changes in the elderly
- increased suicide rate (esp. white men older than 85)
- decreased vision, hearing, immune response, bladder control
- decreased renal, pulmonary, GI fxn
- decreased muscle mass, increased fat
high-frequency hearing loss due to destruction of hair cells at the cochlear base (preserved low-frequency hearing at the apex)