Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

Epidemiology > Evaluating the Role of Random Error > Flashcards

Evaluating the Role of Random Error Flashcards

1
Q

If the observed result is false, what could be the 3 alternate explanations?

A
  • Bias
  • Confounding
    • Random Error
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Random Error

A
  • aka chance
  • arises from:
    • measurement errors
    • sampling variability
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are some ways to reduce random error?

A
  • increase sample size
  • repeat a measurement or entire study
  • use an efficient study design
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Hypothesis Testing

A
  • determines if random error/chance causes association
  • P value
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Null Hypothesis

A
  • no association b/w exposure and outcome
  • RR=1, OR=1, RD=0
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Alternate Hypothesis

A
  • is an association b/w exposure and outcome
  • RR≠1, OR≠1, RD≠0
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Define P Value:

A
  • given that H0 is true, the p-value=probability of observed and extreme results by chance only
  • Range: 0-1
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

If p ≤ .05…

A
  • significant
  • reject H0, Accept HA
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

If p>0.05

A
  • not significant
  • do no reject H0
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Problems with use of P-value in research

A
  • Does not:
    • imply medical, biological, or public health significance
    • rule out bias or confounding explanations
    • mean H0 is true
  • P≤0.05 is arbitrary→ judgement errors
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What does the confidence interval tell you

A
  • range of hypotheses that are comparable to the data
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What does a wide confidence interval indicate?

A
  • smaller population size
    • large amount of random error
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what does a narrow confidence interval indicate?

A
  • large sample size
    • small amount of random error
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

If null hypothesis is within confidence interval range, the what would the p-value be?

A
  • P-value> 0.05
  • not significant
    • H0 not rejected
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Confounding

A
  • mixing of effect b/w exposure, outcome, and confounder (3rd variable)
  • exaggerates or minimizes true association
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Criteria to be a confounder?

A
  • Must be associated with:
    • exposure
    • outcome
      • independent of exposure
  • not intermediate step in cause pathway b/w exposure and disease
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What are the effects of confounding?

A
  • account for all or part of association
  • cause overestimate or underestimate of association
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What variables can be potential confounders?

A
  • risk factors for disease
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What are the different ways to control for confounding?

A
  • Design Stage:
    • Randomization (RCT)
    • Restriction
    • Matching
  • Analysis Stage:
    • Stratification
    • Multivariat analysis
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Randomization

A
  • with sufficient sample size
    • control for known and unknown confounders
  • not guaranteed
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Restriction

A
  • restrict admission criteria for study
  • limits individuals in specific category of confounder
  • ex: Race limited by age or height
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is the goal for controlling confounding in design phase

A
  • eliminate or reduce variation in confounding factor b/w compared groups
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Restriction: Advantages and disadvantages

A
  • advantages
    • straight forward
    • convenient
    • inexpensive
  • disadvantages
    • limits generalization
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Matching

A
  • select subject so potential confounders are distributed in identical manner among:
    • exposed and unexposed
      • cohort study
    • case and controls
      • case control study
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Stratification
* evaluate association within homogenous categories (strata) of confounding variable
26
Bias
* systematic error * results in and incorrect measure of association: * creates association when there is not one * bias away from null * Mask association when there Is one * bias towards the null * arise in all study types: * experimental * cohort * retrospective=mostsusceptible * case-control * evaluated but not fixed in analysis design
27
What are the 2 main type of bias?
* selection * observation
28
What type of studies are Selection Bias most likely to occur in? Why?
* most likely to occur in: * case control * retrospective * bc Exposure and outcome occurred at time of study selection
29
What is the solution to selection bias?
* nothing can be done
30
Observation Bias
* error in the info on exposure or outcome from subjects * affects groups unequally * occurs after subject have entered the study * results in incorrect classification of subjects: * exposed vs unexposed * diseased or not
31
What are the different types of observation bias?
* Recall * Interviewer * misclassification
32
recall bias
* remember or report exposures differently * more or less accurate than those w/o disease
33
Interviewer bias
* difference in soliciting, recording or interpreting info
34
misclassification bias
* subjects exposure or disease status is classified wrong * incorrectly reported or recorded
35
Loss of subjects to f/u
* Problem in cohort studies when related to exposure and disease
36
What diseases are appropriate for screening?
* serious disease w/severe consequences * progressive disease & tx is more effective at earlier stage * High Prevalence in DPCP * Detectable pre-clinical phase
37
What are some characteristics of good screening test?
* economical * convenient * free of risk and discomfort * acceptable to large population * highly valid and reliable
38
test validity
* does it accurately identify those with and without preclinical disease * sensitivity * specificity
39
Test reliability
* same result each time
40
2x2 table for screening test outcomes:
41
Define Sensitivity
* probability that people with the disease will test positive * True Positive
42
How do you calculate sensitivity?
a/(a+c)
43
Define Specificity
* probability that people without the disease have a negative test * true negative
44
t
45
How do you calculate specificity?
d/(b+d)
46
define Positive Predictive value
* the likelihood that a positive test result indicates the existence of the disease * how worried should the patient be?
47
How do you calculate positive predictive value?
a/(a+b)
48
define negative predictive value
* likelihood that a negative test result indicates the absence of the disease * how reassured should they be?
49
How do you calculate negative predictive value?
d/(c+d)
50
What do predictive values depend on?
* sensitivity * specificity * prevalence
51
Randomized control Trials
* gold standard for study designs * bc of greater internal validity
52
Steps to conduct RCT
* enroll subject * allocate to tx groups (Tx vs placebo) * randomization * blinding * F/u for relevant period * study groups monitored for outcome * compare rates of outcome in different groups
53
RCT Step 2: Allocate Tx or placebo by randomization. What are the benefits? Overall Goal?
* Benefits: * unbiased assignment * known and unknown confounders are balance * leads to comparability * minimizes selection bias and confounding * Goal: * Groups are identical-all determinants except tx * any difference due to tx
54
RCT: What groups are subjects randomized into?
* Tx Group * New tx * other doses of same tx * Other: Combo therapy * Comparison group * Placebo * Other: usual care (current tx in use)
55
What is the primary objective for using a placebo?
* minimize bias
56
Uses of placebo?
* makes group as comparable as possible * depends on subjectivity of outcome * cannot be done in some situations * pills vs surgery * Allows study to be blinded
57
What is the primary objective of blinding in RCT?
* Prevent bias from affecting results
58
What are the different types of blinding?
* Single-Blind * subjects unaware of treatment group * Double-Blind * Both subjects & investigators unaware of tx groups * cannot be done in some situations (pills vs surgery) * Triple Blind: * Subjects, investigators admin tx, investigators eval outcomes all unaware
59
How to establish cause
* Valid Association * even if valid, not all associations are causal * eliminated alternative explanations
60
Hill's Criteria
* Causality is strengthened by: * temporal sequence * risk factor first * strong association * dose-response relationship * consistent findings * biologic credibility * results of experiment
61
Temporal sequence
* a factor must come before outcome to cause it
62
What types of studies provide the best evidence that causes precedes the effect?
Prospective Cohort Studies Randomized Clinical trials
63
Strength of Association
* Large RR supports cause relationship * by itself, can't conclude cause * bias or confounding * Small RR also possible
64
Presence of Dose-Response relationship
more exposure means greater risk

Epidemiology (6 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions