Who does a case control study compare?
A group of people with disease to a group without
What does a case control study look for?
Prior exposure or risk factor
What basic question does a case control study attempt to answer?
Which equation does a case control study use?
What is the equation for odds ratio?
Who does a cohort study compare?
A group with a given exposure or risk factor to a group without
What does a cohort study try to find out?
Exposure increases the likelihood of disease
Which equation is used in cohort studies?
What is the equation for relative risk?
(a/a+b) / (c/c+d)
What basic question does a cohort study attempt to answer?
"What will happen?"
What does a cross-sectional study consist of?
Data from a group of people to assess frequency of disease (and related risk factors) at a particular point in time
Which basic question does a cross-sectional study attempt to answer?
"What is happening?"
Disease prevalence can show _____ but cannot establish _____?
Risk factor association with disease, causality
What does a twin concordance study compare?
The frequency with which both monozygotic twins or both dizygotic twins develop a disease
What does a twin concordance study measure?
Who are the groups compared in an adoption study?
Siblings raised by biologic vs. adoptive parents
What does an adoption study measure?
Heritability and influence of environmental factors
What does a clinical trial attempt to assess?
Therapeutic benefits of 2 or more treatments, or of treatment and placebo
What three things are necessary for the highest quality of clinical trial?
3. Double blinded
Who is included in the study sample of a Phase I clinical trial?
Small number of patients, usually healthy volunteers
What three variables does a Phase I clinical trial assess?
Who is included in the study sample of a Phase II clinical trial?
Small number of patients with disease of interest
What three variables does a Phase II clinical trial assess?
1. Treatment efficacy
2. Optimal dosing
3. Adverse affects
Who is included in the study sample of a Phase III clinical trial?
Large number of patients randomly assigned either to treatment under investigation or to the best available treatment (or placebo)
What does a Phase III clinical trial compare?
The new treatment to the current standard of care
What does a phase IV clinical trial consist of?
Postmarketing surveillance trial of patients after approval
What does a Phase IV clinical trial detect?
Rare or long-term side effects
What does a meta-analysis consist of?
Pooled data from several studies to come to an overall conclusion
What does a meta-analysis achieve, statistically?
Greater statistical power
What two things may limit the validity of a meta-analysis study?
1. Quality of individual studies
2. Bias in study selection
What is the definition of sensitivity?
Proportion of all people with disease who test positive, or the ability of a test to detect a disease when it is present
What is the equation for sensitivity?
1. TP / (TP + FN)
Does sensitivity rule a disease in or out?
**SNOUT = SeNsitivity rules OUT**
For what situation is a sensitivity value approaching 1 desirable?
Ruling OUT disease
A test with a high sensitivity has a _______?
Low false negative rate
What kinds of diseases are tests with high sensitivity used for screening?
Diseases with low prevalence
What is the definition of specificity?
The proportion of all people without disease who test negative, or the ability of a test to indicate non-disease when disease is not present
What is the equation for specificity?
Does specificity rule a disease in or out?
**SPIN = SPecificity rules IN**
For what situation is a specificity value approaching 1 desirable?
Ruling IN disease
A test with a high specificity has a _______?
Low false-positive rate
What is a test with a high specificity used as?
Confirmatory test after a positive screening test
ELISA has high ________?
Western blot has high ________?
What is the definition of positive predictive value?
The proportion of positive test results that are truly positive, or the probability that a person actually has the disease given a positive test result
What is the equation for positive predictive value?
What is the relationship between disease prevalence and predictive value?
If the prevalence of a disease in a population is low, even tests with high specificity or sensitivity will have low positive predictive values
What is the definition of negative predictive value?
The proportion of negative test results that are truly negative, or the probability that a person is actually free of the disease given a negative test result
What is the equation for negative predictive value?
What is the equation for disease point prevalence?
PP = total cases in population at a given time / total population at a given time
What is the equation for disease incidence?
Incidence = new cases in a population over a given time period / total population AT RISK during that time period
What is prevalence roughly equal to?
Incidence x disease duration
Which kind of diseases have a prevalence > incidence?
Which kind of diseases have a prevalence = incidence?
What should you not forget to account for when calculating incidence?
People currently with disease, or those previously positive for it, are not considered at risk
What is the definition of the odds ratio in case control studies?
The odds of having disease in an exposed group divided by the odds of having disease in unexposed group
Odds ratio approximates ______ if prevalence is not too ______?
Relative risk, high
What is the definition of relative risk in cohort studies?
The relative probability of getting a disease in the exposed group compared to the unexposed group
How is relative risk calculated in terms of percentages?
Percent with disease in exposed group divided by percent with disease in unexposed group
What is the definition and equation for attributable risk?
The difference in risk between exposed and unexposed groups, or the proportion of disease occurrences that are attributable to the exposure (e.g., smoking causes one-third of cases of pneumonia); a/(a+b) - c/(c+d)
What is the definition of absolute risk reduction?
The reduction in risk associated with a treatment as compared to a placebo
What is the equation for number needed to treat?
1/absolute risk reduction
What is the equation for number needed to harm?
What are two definitions of precision?
1. The consistency and reproducibility of a test (reliability)
2. The absence of random variation in a test
What is the definition of accuracy?
The trueness of test measurements (validity)
Random error results in reduced _________?
Precision in a test
Systematic error results in reduced _________?
Accuracy in a test
What is the cause of selection bias?
Nonrandom assigment to study group
What is the cause of recall bias?
Knowledge of presence of disorder alters recall by subjects
What is the cause of sampling bias?
Subjects are not representative relative to general population; therefore, results are not generalizable
What is the cause of late-look bias?
Information gathered at an inappropriate time--e.g., using a survey to study a fatal disease (only those patients still alive will be able to answer the survey)
What is the cause of procedure bias?
Subjects in different groups are not treated the same--e.g., more attention is paid to treatment group, stimulating greater compliance
What is the cause of confounding bias?
Occurs with 2 closely associated factors; the effect of 1 factor distorts or confuses the effect of the other
What is the cause of lead-time bias?
Early detection confused with increased survival; seen with improved screening (natural history of disease is not changed, but early detection makes it seem as though survival has increased)
What is the cause of the Pygmalion effect?
Occurs when a researcher's belief in the efficacy of a treatment changes the outcome of that treatment
What is the cause of the Hawthorne effect?
Occurs when the group being studied changes its behavior owing to the knowledge of being studied
What are four ways that bias in studies can be reduced?
1. Blind studies
2. Placebo responses
3. Crossover studies
In a Gaussian distribution, the mean ? median ? mode?
What does a bimodal distribution consists of?
Two modal peaks
What does a positively skewed distribution have?
Mean>median>mode; asymmetry with tail on right
What does a negatively skewed distribution have?
Mean<median<mode; asymmetry with tail on left
Which variable is least affected by outliers in the sample?
What is the definition of the null hypothesis?
The hypothesis of no difference (e.g., there is no association between the disease and the risk factor in the population)
What is the definition of the alternative hypothesis?
The hypothesis that there is some difference (e.g., there is some association between the disease and the risk factor in the population)
What does a type I (alpha) error is state?
There IS an effect or difference when none exists (to mistakenly accept the experimental hypothesis and reject the null hypothesis)
p = ?
The probability of making a type I error, judged against a preset level of significance (usually <.05); "false positive error"
What does a p value of < .05 state?
There is less than a 5% chance that the data will show you something that is not really there
What does a type II (Beta) error state?
There is NOT an effect or difference when one exists (to fail to reject the null hypothesis when in fact H0 is false)
Beta = ?
The probability of making a type II error; "false negative error"
What is the definition and equation for statistical power?
The probability of rejecting the null hypothesis when it is in fact false, or the likelihood of finding a difference if one in fact exists; 1-Beta
What three variables can affect the power of a study?
1. Total number of endpoints experienced by a population
2. Difference in compliance between treatment groups (differences in the mean values between groups)
3. Size of expected effect
How can one best increase the power of a study?
Increase the sample size
**there is Power in Numbers**
What is the equation for Standard Error of the Mean?
SD/(square root of n)
What percentage of values may be found within 1 standard deviation of the mean?
What percentage of values may be found within 2 standard deviations of the mean?
What percentage of values may be found within 3 standard deviations of the mean?
What is the definition of the confidence interval?
The range of values in which a specified probability of the means of repeated samples would be expected to fall
What is the equation for confidence interval?
mean +/- Z(SEM)
What is the Z score used to calculate the 95% confidence interval?
What does it mean if the 95% confidence interval for a mean difference between 2 variable includes 0?
There is no significant difference and the null hypothesis is NOT rejected
If the 95% confidence interval for odds ratio or relative risk includes 1, then?
There is no significant difference and the null hypothesis is NOT rejected
What does it mean if the confidence interval between two groups overlaps?
These groups are not significantly different
A T-test checks the difference between ______?
The means of 2 groups
**Mr. T is mean**
An ANOVA test checks the difference between ______?
The means of 3 or more groups)
**ANOVA = ANalysis Of VAriance of 3 or more variables**
A X2 (chi-square) test checks the difference between ______?
2 or more percentages or proportions of categorical outcomes (NOT mean values)
**X2 = compare percentages or proportions**
Between which values does the correlation coefficient (r) is always lie?
-1 and +1
The closer the absolute value of r (correlation coefficient) is to 1, the _______ the correlation between 2 variables?
What is the coefficient of determination?
R2 (value that is usually reported)
What does primary prevention attempt to cause?
Prevention of disease occurrence (e.g., HPV vaccination)
What does secondary prevention attempt to cause?
Early detection of disease (e.g., PAP smear)
What does tertiary prevention attempt to cause?
Reduced disability from disease (e.g., chemotherapy)
What is the mnemonic for disease prevention?
Which diseases are reportable in most states?
**Hep, Hep, Hep, Hooray, the SSSMMART Chick is Gone**
Which two reportable diseases are not required to be reported in all 50 states?
1. Hep C
What are the three leading causes of death in the US in infants?
1. Congenital anomalies
What are the three leading causes of death in the US in ages 1-14?
3. Congenital anomalies
What are the three leading causes of death in the US in ages 15-24?
What are the three leading causes of death in the US in ages 25-63?
2. Heart disease
What are the three leading causes of death in the US in ages 65+?
1. Heart disease
What are Medicare and Medicaid?
Federal programs that originated from amendments to the Social Security Act
**MedicarE is for Elderly, MedicaiD is for Destitute**
What three groups is Medicare available to?
1. Patients > 65 years of age
2. Patients < 65 with certain disabilities
3. Patients with end stage renal disease (ESRD)
What are three things are covered by Medicare Part A?
1. Inpatient care in hospitals
2. Skilled nursing hospice
3. Home health care
What are three things covered by Medicare Part B
1. Outpatient care
2. Doctors' services
3. Physical therapy/occupational therapy
What is Medicare Part C?
Stand-alone prescription drug coverage
What is Medicaid?
Federal and state health insurance for people with very low income.
**MedicaiD is for Destitute**