Lecture 4 (Sep 27)

Question 1

Misclassify

Answer 1

Very common error in health research

Question 2

Information (measurement) error leads to

Answer 2

misclassification

Question 3

Non-differential classification (the same in all study groups)

Answer 3

Usually weakens associations – i.e. brings effect estimates (RR, OR, AR) closer to the null value
But not always…
May have misclassified 1.4 % of them but the vast majority was not misclassified

Question 4

Differential (different in different study groups)

Answer 4

Effect estimates may change in any direction, depending on the particular error
Misclassified to much of the data to a point of having no idea whether you should
Ex. Low Birthweight mothers a biased to assume that it is their fault that and the over represent the amount of pesticides they were around

Question 5

Causal Inference

Answer 5

The process of determining whether a cause-and-effect relationship exists between two variables. It aims to answer questions like, “Does X cause Y?” For example, in medicine, researchers might ask, “Does a new drug cause better health outcomes?”
Building Blocks:
Measures of Disease Frequency, Various Study Designs
Results of Research:
Measures of Association

Question 6

Once you have calculated a measure of association, you need to determine if the observed association is

Answer 6

valid and if it is causal

Question 7

Research Evidence Strong evidence is

Answer 7

Strong evidence is

1. Of the lowest possible random sampling error (a statistically significant exposure/outcome association)
2. Based on a good design
   Free of selection and information biases
   Under minimal influence of confounding (next session)

Question 8

Internal validity

Answer 8

refers to the extent to which a study or experiment accurately establishes a causal relationship between the treatment (or independent variable) and the observed outcome (or dependent variable), without being affected by other confounding variables or biases. In simpler terms, it addresses whether the effects observed in a study can be confidently attributed to the intervention or treatment itself, rather than to external factors or flaws in the research design.

Question 9

Generalizability

Answer 9

also known as external validity, refers to the extent to which the findings of a study can be applied or generalized beyond the specific conditions of the research. In other words, it addresses whether the results of a study hold true across different populations, settings, time periods, or variations in the treatment. Requires internal validity.

Question 10

If a study lacks internal validity, external validity

Answer 10

is irrelevant

Question 11

We do not compromise internal validity in an effort to

Answer 11

achieve external validity (generalizability)

Question 12

Internal validity is when

Answer 12

when the effect estimated from the analytic sample is equal to the true causal effect in the study sample

Question 13

External validity is when

Answer 13

the true causal effect in the study sample is equal to the true causal effect in the target population.

Question 14

Four Hallmarks of Health Studies

Answer 14

1. A research question/plausible theory
2. A well thought design to address the research question
3. Measurement of exposure and outcome
4. Analysis to compare groups (measured association)

Question 15

Validity is…

Answer 15

Having fewer errors

Error=Measured value-True value

Question 16

Sources of error (CBC):

Answer 16

Chance (random sampling error)
Bias Systematic error in selection of participants and/or measurement
Confounding (next week)

Question 17

Threats to Validity

Answer 17

Chance (random sampling error)
Bias Systematic error in selection of participants and/or measurement
Confounding (next week)

Question 18

Random Sampling Error is not to be confused with

Answer 18

1) Random error in measurement
Information bias (previous session)
2) Randomization (a process in experimental studies)
Nov 8, 2024

Question 19

Type I error:

Answer 19

jumping the gun
Concluding that there is a treatment effect, or an exposure/outcome association (in the population from which you sampled), when there is NOT

Question 20

Type II error:

Answer 20

missing the boat
Failing to detect a REAL treatment effect or an exposure/outcome association (in the population from which you sampled)

Question 21

Bias

Answer 21

Bias refers to a systematic error in the design or conduct of a study
When bias occurs in a study the observed association between the exposure and outcome will be different from the true association

Most biases relate to the study design and procedures and can be classified into two categories:

Selection bias
Information bias (due to measurement error, last week)

Question 22

Information Bias vs Selection Bias:

Answer 22

Information bias occurs when there is a systematic error in the way data on the variables (e.g., exposure or outcome) is measured, collected, or classified in a study. This can lead to incorrect or misleading information being used in the analysis, potentially affecting the results.
Selection Bias: Selection bias occurs when the participants included in a study (or excluded from it) are not representative of the target population. This can happen during the selection or retention of participants and leads to systematic differences between those who are studied and those who are not.

Question 23

Why does Selection Bias Happen?

Answer 23

NOT an Error Associated with Sampling, recall week 2

Question 24

Types of Selection Bias

Answer 24

Inappropriate Control Selection (Control-Selection Bias) > Case control

Differential Participation > Case control, cohort

Differential Loss to Follow Up > Cohort Experimental

Question 25

Examples of Selection Bias

Answer 25

Volunteer bias
Non-response bias
Membership bias
Loss to follow-up bias

Question 26

Volunteer bias

Answer 26

Volunteers are more health-conscious or from a different socio-economic group
Differential exposure
Effect of interventions for enhancing physical activity in older adults

Question 27

Non-response bias

Answer 27

Those suffering from a disease with a particular belief
Differential outcome

Question 28

Membership bias

Answer 28

Healthy worker effect
Service in Vietnam reduced mortality rates (Crane et al, 1997)

Question 29

Loss to follow-up bias

Answer 29

In clinical trials or longitudinal studies the sickest usually leave the study early

Question 30

Examples of Selection Bias

Answer 30

Berkson’s bias

Question 31

Berkson’s bias

Answer 31

When cases and controls for a study are recruited from hospitals and therefore are more likely than the general population to have comorbid conditions
For example, assume that two diseases, sickle cell anemia (exposure) and asbestosis (outcome), are not associated in the source population. However, individuals with both diseases are more likely to be hospitalized.

Question 32

2 year long randomized controlled trial of medication use and weight loss in adults with obesity. Three treatment (exposure) groups: Metformin, Orlistat, or Placebo

Answer 32

Participants enrolled in this study with the intention and hope of losing weight

During the 2 year intervention, 10% of the Metformin group dropped out, 25% of the Orlistat group dropped out, and 35% of the Placebo group dropped out

The loss to follow-up also differed by weight loss (outcome) and side effects of the drugs (related to exposure)

Question 33

Oral Contraceptive Pills (OCP) and Deep Vein Thrombosis (DVP)