Interpreting results Flashcards
Define descriptive statistics
Used to organise or summarise data collected from a sample population
Define inferential statistics
Uses data collected from a sample population to make generalisations about the target population
Define independent variable
An entity that is manipulated in the study
- Also known as experimental variable
Define dependent variable
An entity that is affected by the change in the value of the independent variable
- Also known as outcome variable
How do you calculate incidence?
Incidence = Number of new cases / population size
- Measure of the risk of a disease
How do you calculate point prevalence?
Point prevalence = Number of people with disease at a given time / size of population at the same time
Define intention to treat analysis
All participants are included in the analysis regardless of whether they completed the study
- Pragmatic approach
- Mirrors real life scenario
Define last observation carried forward
Last recorded results of individual who drop out are incorporated into the results
- Used in intention to treat analysis
Define worst case scenario analysis
Subjects who drop out are recorded as non responders with worst possible outcomes
- Used in intention to treat analysis
Define imputation
Missing data is substituted with plausible values to allow data analysis to proceed
- Used in intention to treat analysis
Define sensitivity anaylsis
Assumptions are made when the missing values are put in
Define risk
The probability of something happening
- Expressed as p (number between 0-1) or percentage
- Number of times event occurs / total number of possible events
Define odds
Way of expressing chance
- Expressed as ratio or fraction
- Odds is the ratio of the number of times an event is likely to occur / number of times it is likely not to occur
What is a contingency table?
2x2 table comparing risk and odds across 2 groups
- Rows consist of exposure
- Columns consist of outcome event status
Define control event rate (CER)
Outcome event rate in control group
- outcome event in controls / outcome event in controls + no outcome event in controls
Define experimental event rate (EER)
Outcome event rate in experimental group
- outcome event in experimental subjects / outcome event in experimental subjects / no outcome event in experimental subjects
Define absolute risk reduction (ARR)
Control event rate - experimental event rate
- Also known as absolute benefit increase
- If negative number, then called absolute risk increase
Define relative risk (RR)
Experimental event rate / control event rate
Define relative risk reduction (RRR)
Control event rate - experimental event rate / control event rate
- Also known as relative benefit increase
- If negative number, then called relative risk increase
Define number needed to treat (NNT)
1 / absolute risk reduction
ARR = CER - EER
- Number of subjects who must be treated with intervention compared with control for one additional subject to experience the beneficial outcome
- If negative number, then can be expressed as NNH
Define odds ratio
odds of outcome in exposed group / odds of outcome in control group
What does it mean if the relative risk is equal to 1?
No risk difference between the two groups
What does it mean if the relative risk is >1?
Increased risk of the outcome in the experimental group
What does it mean if the relative risk is <1?
Reduced risk of the outcome in the experimental group