Week 2 Flashcards
What are the two overarching types of study designs?
Descriptive and analytic study designs
What is the purpose of a descriptive study design?
To simply examine (describes) exposures (IV) and outcomes (DV).
Doesn’t establish any relationship between exposures and outcomes.
What is the purpose of an analytical study design?
To establish a link between the exposure and outcome.
How is causation established?
Correlation is established, then association, then eventually with enough research, causation.
Name four types of descriptive study designs.
- Case study
- Case report
- Case series
- Cross-sectional
Name the two types of analytical study designs.
- Observational designs
- Intervention/experimental designs
Name three observation study designs.
- Cross-sectional
- Ecological/correlational
- Cohort
What are two types of intervention/experimental study designs?
- Randomised design (Randomised Controlled Trials [RCT])
- Non-Randomised design (Quasi-experimental design)
How to write a research question for an intervention/experimental design?
PICO
Population (of interest)
Intervention
Control group (Comparison)
Outcome (variable measured to see if intervention worked)
How to write a research question for an observational design?
PECO
Population (of interest)
Exposure (determinant; risk factor; beneficial factor)
Comparison group (people without exposure)
Outcome (variable with visible link to exposure)
Name three common measures of morbidity.
- Prevalence
- Cumulative incidence
- Incidence rate
Describe prevalence.
The number of existing cases in a population at a point in time or during a period of time.
What is the formula for prevalence?
number of cases in population / total population at that time
(calculate as percentage with 2 decimal points)
Describe cumulative incidence rate.
Number of new cases over a specified period of time divided by total number of people in the population at risk in the beginning.
What is the formula for cumulative incidence?
New cases during time period / At risk or disease-free population at the beginning of the time period
Describe incidence rate.
Number of new cases during a specific period of time divided by the total disease free person time in a population at risk.
What is disease-free time?
Collective time when people are at risk. It can be measured in person-years, person-months, person-days etc.
What is the formula for incidence rate?
New cases during a specified time period / total disease-free time
Define a sample.
A subset of a population of interest.
What is sampling?
The process of how we choose a subset of a population.
What is one important characteristic of a sample?
Representativeness: a sample must be representative of the population
What are probability samples?
Samples usually obtained using random chance selection where everyone has equal chance to be in the sample.
What are two advantages of probability samples?
- Representative of the population
- Meets the requirement for statistical tests and statistical inference
What is sampling error?
The difference between sample results and the true value for the population.
What is another term for sampling error?
Chance
What is chance?
The likelihood a result from a sample is produced by random factors.
How to ensure results are real and not due to chance factors?
Using statistical tests:
P value high (>5%) = higher likelihood of results due to chance
P value low (<5%) = lower likelihood of results due to chance
What are the two categories of sampling?
- Probability sampling
- Non-Probability sampling
What is random sampling?
Probability sampling
What is non-random sampling?
Non-probability sampling
What three factors affect the choice of sampling method?
- Research question
- Method of which data is collected
- Availability of a good sampling frame
Name the four types of probability sampling methods.
- Simple random sample
- Systematic random sample
- Stratified random sample
- Cluster sample
What is simple random sampling?
Every subject has an equal opportunity / probability to be in the sample
What is systematic random sampling?
Selection of specific items in a series according to some predetermined sequence. Origin of the sequence should be controlled by chance.
What is stratified random sampling?
When the population is subdivided into smaller homogenous groups (strata) to get a more accurate representation.
What are the two steps to performing stratified random sampling?
- Breaking the population into non-overlapping groups (strata)
- Simple random sample extracted from each stratum
What is a cluster sample?
Sampling of naturally occurring “clusters” (e.g., schools, households, suburbs etc.)
What are the four types of non-probability samples?
- Convenience sample
- Quota sample
- Purposive sample
- Snow ball sample
What is a Convenience Sample?
Selecting anyone who agrees to take part when recruited easily and quickly with minimal effort.
What is a Quota Sample?
Similar to stratified sample.
Researcher decides which strata are relevant and how many should be in each quota. Researcher selects them for best fit non-randomly.
What is a Purposive Sample?
Researcher selects respondents who best meet the purpose of the study. Good for experienced researchers with prior knowledge and skill.
What is a Snow Ball Sample?
A person fitting the criteria is interviewed and asked if they know others fitting the same criteria.
What are the two types of validity?
- Internal validity
- External validity
What is Internal Validity?
The results are true or closer to the truth for those who took part in the study.
What is External Validity?
The extent to which the results can be generalised to those outside of the study.
What two things affect reliability?
Random error and systematic error
What are three types of bias?
- Selection bias
- Information bias
- Confounding bias
