Biostatistics and Preventive Medicine Flashcards
(112 cards)
1
Q
Bias (Recruiting participants)
A
Selection bias
2
Q
Colon Cancer Screening
A
Screening is by colonoscopy after the age of 50 every 10 years
3
Q
What happens to incidence and prevalence if additional Federal research dollars are targeted to a specific condition
A
- I = no change
- P = no change
4
Q
Diagnostic Odds Ratio [DOR]
A
= LR+ / LR-
5
Q
Late-look bias
Definition, association(s), solution(s)
A
- Severely diseased individuals are not uncovered
- Early mortality
- Stratify by severity
6
Q
Dependent Probability
A
P = P(A) * P(B I A)
7
Q
Number needed to treat (NNT)
A
= 1 / ARR
8
Q
Sensitivity (Recall, True Positive Rate [TPR])
A
= TP / (TP + FN)
= 1 - False Negative Rate [FNR]
- SNOUT
9
Q
Incorrect results of statistical hypothesis
A
- Type I error (alpha): stating that there is an effect or difference when none exists (null hypothesis incorrectly rejected in favor of alternative hypothesis). (H0,H1)
- Type II error (beta): stating that there is not an effect or difference when one exists (null hypothesis is not rejected when in fact it is false). (H1,H0)
10
Q
Proportionate Mortality Rate (PMR)
A
Deaths from cause / All deaths
11
Q
Selection bias
Definition, association(s), solution(s)
A
- Sample is not representative
- Berkson bias (population selected from hospital), healthy worker effect (study population is healthier than general population), Non-response bias (people included in a study are different from those who are not)
- Randomization and independent sample
12
Q
Crude Rate
A
Actual measured rate for the whole population
13
Q
Correct results of statistical hypothesis
A
- Stating that there is an effect or difference when one exists (null hypothesis [H0] is rejected in favor of alternative hypothesis [H1]). (H1,H1) which equals power (1-beta)
- Stating that there is not an effect or difference when none exists (null hypothesis not rejected). (H0,H0) which equals a correct result
14
Q
Binomials
A
- Every term expanded is nCr x^n-r * y^r
- We can find a term that contains the factor x^r in an expansion of (x+y)^n by using nCn-r * x^r * y^n-r
15
Q
What happens to incidence and prevalence if behavioral risk factors are reduced in the population at large
A
- I = decrease
- P = decrease
16
Q
t-test
A
- 1 interval and 1 nominal
- 2 groups only
17
Q
Randomized Controlled Trials (RCTs)
Definition, Advantages, Disadvantages
A
- Experimental, prospective study in which subjects are randomly assigned to a treatment or control group. Could be single or double blinded study
- Ad:
- Minimize bias
- Potential to demonstrate relationships because exposure is assigned randomly, which minimize confounding
- Dis:
- Costly and time consuming
- Some interventions (like surgery) are not amenable to masking
18
Q
Absolute Risk Reduction (ARR)
A
= [c/(c+d)] - [a/(a+b)]
19
Q
What happens to incidence and prevalence if number of persons dying from the condition increases
A
- I = no change
- P = decrease
20
Q
Odds Ratio (OR)
A
= (ad) / (bc)
21
Q
What happens to incidence and prevalence if new effective vaccine gains wide spread use
A
- I = decrease
- P = decrease
22
Q
Outcomes (definitions)
A
Results of each trial
23
Q
Positive Predictive Value [PPV] (Precision)
A
= TP / (TP + FP)
- Varies directly with prevalence
24
Q
False Discovery Rate [FDR]
A
= FP / (FP + TP)
25
Type II error (beta)
- Also known as false-negative error
- It is related to statistical power (1-beta), which is the probability of rejecting the null hypothesis when it is false.
- To increase power and reduce beta error:
* Increase sample size
* Increase expected effect size
* Increase precision of measurement
26
Randomized Clinical Trials (RCTs) phases
- Phase I: small # of healthy volunteers to assess safety, toxicity, pharmacokinetics and pharmacodynamics
- Phase II: small # of patients with disease of interest to assess treatment efficacy, optimal dosing, adverse effects
- Phase III: large # of patients randomly assigned either to treatment under investigation or the best available treatment (or placebo) to compare the new treatment to the current standard of care
- Phase IV: post-marketing surveillance of patients after treatment is approved to detect rare or long term adverse effects. can result in treatment being withdrawn from market
27
Probability of mutually non-exclusive events
P(A union B)= P(A) + P(B) - P(A intersection B)
28
Repeated measures ANOVA
- 1 interval and 1 nominal
| - More than 2 groups, linked data
29
Cross-Sectional Study
| Definition, Advantages, Disadvantages
- People in the population are examined the presence of a disease of interest at a given point in time (prevalence study)
- Ad:
* Provide an efficient means of examining a population
* Can be used as a basis for diagnostic testing
* Can be used to plan which health services to offer and where
- Dis:
* Cannot determine causal relationships
* Risk or Incidence cannot be directly measured
30
Confidence Interval (CI)
- Range of values within which the true mean of the population is expected to fall, with a specified probability
- CI = mean +/- Z * (SEM)
- For the 95% CI, Z= 1.96 (95% CI corresponds to p=0.05)
- For the 99% CI, Z= 2.58
31
Osteoporosis Screening
- Every women should be screened with bone densitometry at the age of 65 by DEXA scan
- Prophylaxis with bisphosphonates to increase bone density
32
One-way ANOVA
- 1 interval and 1 nominal
| - 2 or more groups
33
Diabetes Mellitus Screening
- Screening with fasting blood glucose (2 measurements over 125) or HbA1c < 6.5% for patients that have hypertension and/or hyperlipidemia
- No clear recommendation for age to start screening in general population
34
Disease Rate
of actual cases / # of potential cases
35
Number needed to harm (NNH)
= 1 / AR
36
Tertiary Disease Prevention
Aims to reduce the disability or morbidity resulting from disease like some treatments and surgeries
37
Prevalence types
- Point prevalence
| - Period prevalence
38
Probability of an event
P(A) = n(A) / n(S)
39
Permutations
- Order is important
- When all objects are taken n!
- When number of objects taken at a time from n nPr = n! / (n-r)!
40
F-Score
- Harmonic mean of precision (PPV) and recall (Sensitivity)
| - = 2 * [(precision * recall) / (precision + recall)]
41
Indications of Pneumococcal vaccination
- Everyone above age of 65
- Cochlear implant
- CSF leak
- Alcoholics
- One vaccine above 65 only
- Single revaccination after 5 years if the patient is immunocompromised or the first injection was prior to age 65
42
Sample points (definition)
Elements of the sample space
43
Relative Risk (RR)
= a/(a+b) / c/(c+d)
44
Trial (definition)
A repetition of experiment
45
Relative Risk Reduction (RRR)
= 1 - RR
46
Specific Rate
Actual measured rate for subgroup of population
47
Cohort Study
| Assess what, Method(s) for data analysis
- Single risk factor affecting many diseases
| - Relative risk to estimate risk
48
Independent Probability
P = P(A) * P(B)
49
Abdominal Aortic Aneurysm Screening
- All men above age of 65 with a history of smoking should be screened with an ultrasound
- Aneurysm should be repaired if it is wider than 5 cm
- Also screen 65-75 with a +ve family history
50
What happens to incidence and prevalence if long-term survival rates for the disease are increasing
- I = no change
| - P = increase
51
Probability of mutually exclusive events
P(A union B)= P(A) + P(B)
52
Combinations
- Order is not important
- nCr = n! / r! (n-r)!
- nC0= 1
- nCn= 1
53
Observer-expectancy bias
| Definition, association(s), solution(s)
- Researcher's beliefs affect outcome
- Pygamlion effect (experimenter expectations inadvertently communicated to subjects, who then produce the desired effects
- Double blinded design
54
False Positive Rate [FPR] (Fall out)
= FP / (FP + TN)
| - Type I error
55
Primary Disease Prevention
A method used to stop the disease before it starts like immunization and behavioral counseling
56
Experiment (definition)
An activity with an observable result
57
Normal Distribution
- Mean = Median = Mode
- 1 SD = 34% (68% on both sides)
- 2 SD = 47.5% (95% on both sides)
- 3 SD = 49.9% (99.7% on both sides)
58
Case-fatality rate
Deaths from cause / # of persons with the disease or cause
59
Positive Likelihood Ratio [LR+]
= TPR / FPR
60
Standardized Rate (Adjusted Rate)
Adjusted rate to make groups equal on some factor
61
Positive Skew Distribution
- Mean > Median > Mode
| - Asymmetry with longer tail on right
62
What happens to incidence and prevalence if recovery from the disease is more rapid than it was 1 year ago
- I = no change
| - P = decrease
63
Breast Cancer Screening
- Mammography between (40-50). Age of maximum benefit is > 50 is clear in decreasing mortality
- Screening is done every 2 years and can be stopped at age of 75
- Selective estrogen receptor modulators (SERMs) like tamoxifen and raloxifene used as a prophylaxis in patients who are free of disease but with multiple first degree relatives with breast cancer (at least 2) results in a 50% to 60 % reduction in breast cancer
- BRCA comes +ve, management remains undetermined
64
Hypertension Screening
For all above age of 18 every 2 years
65
Procedure (design) bias
| Definition, association(s), solution(s)
- Parts of study do not fit together
- Non-comparable control group
- Random assignment
66
Case-Control Study
| Definition, Advantages, Disadvantages
- A series of cases are identified and a set of controls are sampled from the underlying population to estimate the frequency of exposure in the population at risk of the outcome
- Ad:
* Use smaller groups than cohort, thereby reducing cost
* Can be used to study rare diseases and easily examine multiple risk factors
- Dis:
* Cannot calculate incidence or prevalence, but an odds ratio can be used to estimate a measure of relative risk
* Retrospective data may be inaccurate owing to recall or survivorship biases
67
Bias (Performing study)
- Recall bias
- Measurement bias
- Procedure bias
- Observer-expectancy bias
68
Precision and Errors
- Increased precision leads to increased statistical power (1-beta) and decreased standard deviation
- Random error decreases precision
69
Confidence Interval (CI) interpretation
- If the 95% CI for a mean difference between 2 variables includes 0, then there is no significant difference and H0 is not rejected
- If the 95% CI for odds ratio or relative risk includes 1, H0 is not rejected
- If the CIs between 2 groups do not overlap, that means statistically significant difference exists
- If the CIs between 2 groups overlap, that means no significant difference exists
70
Probability of complement of an event
P(A')= 1 - P(A)
71
Negative Predictive Value [NPV]
= TN / (TN + FN)
| - Varies inversely with prevalence
72
Prevalence
- # of existing cases / Total # of people in a population
| - = Incidence * Duration of disease
73
Conditional Probability
P(B I A) = P(A intersection B) / P(A)
74
Variance
= (SD)^2
75
Incidence
of new cases / # of people at risk
76
Sample space (definition)
Set of all possible outcomes
77
False Omission Rate [FOR]
= FN / (FN +TN)
78
Cohort-Study
| Definition, Advantages, Disadvantages
- A group of people is assembled, none of whom has the outcome of interest, but all of whom could potentially experience the outcome. Incidence of outcome events is compared in the 2 exposure groups
- Ad:
* The only way to directly determine incidence
* Can be used to assess the relationship of a given exposure to many diseases
* In prospective studies, exposure is elicited without bias from a known outcome
- Dis:
* Time consuming and expensive
* Assess only the relationship of disease to a few exposure factors
* Require many subjects, which makes it difficult to study rare diseases
79
Measurement bias
| Definition, association(s), solution(s)
- Gathering info distorts it
- Hawthorne effect (subject's behavior is altered because they are being studied)
- Control group/placebo group and using objective, standardized, and previously tested methods of data collection that are planned ahead of time
80
Negative Likelihood Ratio [LR-]
= FNR / TNR
81
What happens to incidence and prevalence if contacts between infected persons and non-infected persons are reduced for airborne infectious disease
- I = decrease
| - P = decrease
82
Accuracy and Errors
Systematic error decreases accuracy
83
Receiver Operating Characteristic (ROC) Curve
- Plotting sensitivity (y axis) against 1 - specificity (x axis)
- The more the area under curve is the more better the test
- More sharp plot on the y axis more better the test isC
84
Attack Rate
Same as incidence but during an epidemic
85
Chi-square
- 2 nominal
| - Any # of groups
86
Recall bias
| Definition, association(s), solution(s)
- Subjects cannot remember accurately
- Retrospective studies
- Multiple sources to confirm info and decrease time from exposure to follow-up
87
Specificity (True Negative Rate [TNR])
= TN / (TN + FP)
= 1 - False Positive Rate [FPR]
- SPIN
88
Trade off between sensitivity and specificity
- Possible cutoff values are ( A: 100% sensitivity, B: practical compromise between sensitivity and specificity, C: 100% specificity)
- Lowering the cutoff value (from B to A) will increase FP and decrease FN thereby increases sensitivity and NPV while decreases specificity and PPV
- Raising the cutoff value (from B to C) will increase the FN and decrease the FP thereby increases specificity and PPV while deceases sensitivity and NPV
89
Negative Skew Distribution
- Mean < Median < Mode
| - Asymmetry with longer tail on left
90
Case-Control Study
| Assess what, Method(s) for data analysis
- Many risk factors for a single disease
| - Odds ratio to estimate risk
91
What happens to incidence and prevalence if contacts between infected persons and non-infected persons are reduced for non-infectious disease
- I = no change
| - P = no change
92
Events (definition)
Subset of the sample space
93
Matched pairs t-test
- 1 interval and 1 nominal
| - 2 groups, linked data pairs, before and after
94
Cross-Sectional Study
| Assess what, Method(s) for data analysis
- Association of a risk factor and a disease
| - Chi-square to assess association
95
Accuracy [ACC]
= (TP + TN) / Total population
96
Lipid Screening
- Cholesterol and LDL measurement is recommended for healthy individuals when:
* Men are above age 35
* women are above age 45
- It is recommended for all patients with diabetes, hypertension, coronary artery disease or equivalent like carotid, aortic or peripheral artery disease
97
Standard error of th mean (SEM)
= SD / square root of n
98
Crude Mortality Rate
Deaths / population
99
Measures of dispersion
- Standard deviation
| - Standard Error of the Mean (SEM): it is decreases as sample size (n) increases
100
What happens to incidence and prevalence if new effective treatment is initiated
- I = no change
| - P = decrease
101
Pearson Correlation
- 2 interval
- Is there a linear relationship?
- r is always between -1 and +1. The closer the absolute value of r to 1, the stronger the linear correlation between the 2 variables
- Positive r value means positive correlation (variables are directly related)
- Negative r value means negative correlation (variables are inversely related
- Coefficient of determination = r^2 (value that is usually reported)
102
Prostate Cancer Screening
- 25% of patients with prostate cancer have normal PSA levels
- 25% of those with elevated PSA levels have no prostate cancer
- No benefit of PSA on mortality
- Do it if the patient asks for it
103
Type I error (alpha)
- Also known as false-positive error
- It is judged by p value. if p < 0.05, then there is less than a 5% chance that the data will show something that is not really there
104
Cause-specific mortality rate
Deaths from cause / population
105
Bias (Interpreting results)
- Confounding bias
- Lead-time bias
- Late-look bias
106
Attributable Risk (AR)
= [a/(a+b)] - [c/(c+d)]
107
Secondary Disease Prevention
The detection of the disease early in its course to reduce the associated morbidity and mortality like screening tests
108
Cervical Cancer Screening
- Pap smear is done from 21 to 65 years of age every 3 years
- Adding HPV testing to pap smear increases interval to 5 years
- HPV vaccine is routine for all women between ages of 11 and 26
- Chlamydia screen for women 15-25 years old
109
Indications of Influenza vaccine
- Everyone yearly
- Healthcare workers
- Pregnant women
110
False Negative Rate [FNR] (Miss Rate)
= FN / (FN + TP)
| - Type II error
111
Confounding bias
| Definition, association(s), solution(s)
- Unanticipated factors obscure results
- Hidden factors affect results
- Multiple/repeated studies, Cross-over studies (subjects act as their own controls), Matching (patients with similar characteristics in both treatment and control groups), Restriction and Randomization
112
Lead-time bias
| Definition, association(s), solution(s)
- Early detection confused with increased survival
- Benefits of screening
- Measure "back-end" survival (adjust survival according to the severity of disease at the time of diagnosis)
