module 1 lesson 4 Flashcards Preview

Biostatistics > module 1 lesson 4 > Flashcards

Flashcards in module 1 lesson 4 Deck (36):

Ecological study design

data representing entire population used to evaluate an entire population


Why is study design important

The purpose of a study design is to organize the collection of relevant information to provide strong evidence for a causal relationship between a factor of interest and the development of a health outcome.


Counterfactual outcomes

the ideal experiment:
people are subject to exposure and followed for a period of time and calculate the incidence proportion (risk for exposure - Re)
Now turn back time so the same people are in the original state at the same time prior to exposure. Follow for the same period of time and caculate incidence proportion (risk for unexposed - Ru)
A causal effect of exposure is defined as Re-Ru


Four major reasons study result does not represent a true effect:

-lack of temproality
-lack of validity due to confounding
-lack of validity due to bias
-lack of validity due to chance


How can statistical analysis assist in establishing association versus effect

- stat analysis can est association, but not necessarily true effect
-can help removing confounding effects and dealing with chance
NOT helpful in dealing with biases and lack of temporality


Categories of study design

Observational: prospective, retrospective
Experimental: randomized parallel, randomized crossover, cluster randomized parallel, quasi-experimental
Case control- cumulative, density, case-cohort
cross sectional



Natural experiments - investigator does not control exposure
study groups often not comparable
**research on harmful factors must use this approach


Prospective study

study starts in real time and entire study cohort is at risk at the start of the study



study starts after the health outcome has occurred; entire study cohort is "at risk"some time in the past


Strengths of observational study

- good evidence is needed for a risk factor
- exposure is rare
-desire accurate measure of exposure
- little known about exposure


Limitations of observational study

relatively expensive
- lengthy
- difficult to recruit
-loss to follow up


Experimental cohort

investigator manipulates exposure
usually subjects randomly assigned to groups
used only when tx is beneficial
BEST results


Types of experimental study designs

- Randomized Parallel
- Randomized cross over
- Cluster randomized parallell
- Quasi experimental trial


Randomized parallel

individuals are randomized to experimental groups
All groups followed in parallel over time
Most effective


Randomized cross over

individuals randomly experience all group treatments in sequence
efficient for some treatment effect combinations
requires tx and effect short lived


Cluster randomized parallell

collections of individuals randomized to experimental groups
Allows trials to be conducted in restricted settings


Quasi experimental trial

non-random assignment of individuals or colldections of individuals


Basic sequence of data collection in case control study

-identification of individual with health outcome
- individual without health outcome are identified
- presence of factor of interest determined for cases and controls at an appropriate time in past


Strengths of case control

-desirable if health outcome is rare
-more efficient, less expensive, shorter in duration
- desirable if little is known about risk factors for the outcome
-preferred if follow up is difficult


Limitations of case control

can't directly estimate risk - only risk ratio
exposure based on recall or past record (bias)
est temporality


Cross sectional study design

Assess prevalence of population characteristics at a "point in time"
Major limitations: lacks temporal relationship
odds ratio used as measure of association
often based on survey data
inexpensive and quick


Sampling in cross sectional studies

probability or representative sample -sampling scheme that provides accurate measures for the target population
-simple random
-stratified random
systematic random

Nonpropability or convenience sample - only representative of sampled population


Ecological study design

data representing entire population
exposure status and outcomes status are single values applied to entire population


Ecological fallacy

when based on aggregate data, may not represent association that exists on individual basis. Other factors may be responsible.


Which of the following is a limitation of a cross sectional study resulting from lack of follow up:
a. high cost
b. lack of generalizability
c. ecological fallacy
d. lack of temorality

d. Lack of temporality


which of the following is a limitation of an ecological study that results from the use of aggregate data:
1. lack of generalizability
2. low cost
3. lack of temporality
4. ecological fallacy

4. Ecological fallacy


Which of the following would not be a good reason for a case control study design?
1. when little is known about health effects of rare exposure
2. when the disease of interest has a long induction and latent period
3. when exposure data are expensive to obtain
4. when the disease of interest is rare

3. when exposure data are expensive to obtain


You are interested in finding out whether middle aged men who have premature heartbeats are at greater risk of developing an MI. Baseline EKG are obtained on men 35 yr and older working in law enforcement in SD. the baseline EKG are classified as irregular or regular. over the next five years, new cases of MI are counted and used to compare those with and without irregularities. Which of the following describes this type of study?
1. ecological
2. retrospective cohort
3. cross sectional
4. case control study
5. Prospective cohort study

5. Prospective cohort study


The United Mine workers union is concerned about risk of lung cancer in uranium miners. The union has funded a retrospective cohort study to determine the risk. Which of the following statements fits this study design.
1. 10 yr post start of study, miners examined for lung cancer
2. information about past exposure was obtained from company records
3. information about exposure was obtained by direct measurement at the start of the study
4. data on current exposure was obtained for miners in different states

2.information about past exposure was obtained from company records


Which of the following is an example of the influence of randomization in an experimental study (assume the study is large so randomization is effective?
1. None of the choices
2. The mean age of participants is the same for all groups being compared
3. The participants do not know their assignment
4. There is no loss to follow up

2. The mean age of participants is the same for all groups being compared


An intervention study to evaluate the efficacy of a nutrition education program randomly assigned 20 schools to either the nutrition education program or a placebo program. This is an example of which type of study?
1.cluster-randomized parallel
2. randomized crossover
3.randomized parallel
4. case control
5. Prospective cohort

1. cluster randomized parallell


Which of the following best describes when randomization occurs in an experimental study?
1. After recruitment of participants and before the start of follow up
2. After the start of follow up and before the development of the health outcome of interest
3. After the development of the health outcome of interest
4. before recruitment of participants

1. After recruitment of participants and before the start of follow up


In a study to assess the possible association between alcohol consumption and ischemic heart disease mortality the age adjusted death rate from ischemic heart disease and the per capita consumption of alcohol was determined for various countries around the world. Which type of study is this?
1. ecological
2. Prospective
cross sectional
3. none of these
4. case control

1. ecological


A study is performed to assess wheter there is an association between exposure to second hand smoke in infancy and developmental delay. 50 children with developmental delay and 50 children with normal development are selected for investigation. Parents are asked questions to assess smoke exposure in infancy.
1. cross sectional
2. ecological
3. prospective cohort
4. case control
5. none

4. case control


A study design to evaluate impact of a daily MTV on academic performance. 160 students randomly assigned to MTV or placebo for 20 days then given standardized test

Randomized parallel trial


30 subjects randomly assigned to dietary supplement or placebo for 14 days then bp taken after 1 week the subjects receive placebo

randomized cross over