EAB - study design and summarising data Flashcards
What is an RCT?
- Intervention study
- Choice of treatment/intervention allocated randomly
- Typically randomised to new vs current or placebo treatment
Why do we need to randomise in RCTs?
- Ensures patients’ characteristics don’t affect which treatment they receive
- Unbiased
- Treatment groups balanced
- Any differences in outcome can be attributed to treatment
- Fair test of efficacy
- Usually use computer-generated random list
what is the gold standard for research studies
RCT
What are 2 limitations of RCTs?
- Can be expensive and difficult to organise
- Some interventions are impossible or unethical to randomise to
- ## e.g. impact of lead on children’s intelligence
What are cohort studies?
- Observational study - no intervention
- Subjects observed in natural state (real world)
- Investigates causes or factors associated with disease (or condition)
- Selects group of healthy individuals
- Follow-up to monitor disease state and possible risk factors over time
- Disease state (e.g. yes/no) according to risk factor status (e.g.
smoking yes/no) - Usually prospective (but retrospective designs may be used)
What are the advantages of cohort studies?
- Data is collected prospectively, so estimates are less likely to be biased than those from a case-control
- RCTs can only investigate potential benefits for ethical reasons
- Imbalance between exposed and unexposed can be corrected
- Cohort studies can look at exposure to treatment and harm
eg impact of lead on children’s intelligence
What are case control studies?
- Observational study - no intervention
- Subjects observed in natural state (real world)
- Investigates causes or factors associated with disease (or condition)
- Selects group with disease: ‘cases’
- Choose comparator group without disease: ‘controls’
- Compare cases and controls with respect to possible risk factors
- Usually retrospective
What are the limitations of a case-control study?
x Choice of control group affects comparison
x Data reported by subjects or from records - usually retrospective so may be incomplete, inaccurate or biased
what are advantages of case control studies
✓ BUT often quick to do and inexpensive!
✓ Evidence from case-control studies may be used in planning further research
What are cross-sectional studies?
- Observational study
- Subjects observed in natural state (real world)
- Collect data for each subject at one point in time only
- Similar to a cohort study, but without follow-up
What are the limitations of cross-sectional studies?
- Useful for:
*measuring prevalence of a disease/condition- e.g. % in population with asthma - surveys of attitudes/views/behaviours -e.g. patient satisfaction, alcohol drinking
- Not useful for looking at cause & effect
out of RCT, case control, cohort, and cross sectional, which one is intervention and which one is observational?
RCT = intervention
CROSS SECTION, COHORT, CASE CONTROL = observational
What are 2 types of quantitative data?
- Continuous: lies on continuum – any value valid between range e.g. weight, height
-
Discrete: data can only take certain values – usually integers,
often counts e.g. number of children in a family
What is categorical data?
Individuals fall into one of a number of separate categories, Can be 2, 3 or more categories:
what kind of data is made up of 2 categories
2 categories: dichotomous or binary data
what kind of data is made up of MORE THAN 2 categories
can be ordered or unordered
what is the difference between ordered and unordered?
Ordered data has a specific sequence or arrangement, like a list of numbers sorted from smallest to largest. Unordered data doesn’t have a defined sequence, like a set of items in a bag without any particular order.
what are 2 types of ‘centre of data’
- Mean (arithmetic average)
- Median (middle value when data ranked)
what are 4 types of ‘spread of data’
- Range (min, max; useful as descriptor)
- Standard deviation (‘SD’; shows spread of data; same units as data)
- Variance = SD2
- Interquartile range (IQR; middle 50% of ordered data when data split into
How do you calculate standard deviation?
- find d2 by:
find mean
minus each value from mean
square this value^ - d2/ n-1 (where n is the number of data point)
- then square root it to get SD
what kind of summary should you use for continuous data?
SD
what kind of summary should you use for continuous data with skew?
consider IQR as well
What is a histogram used to show?
distribution of continuous data
What is a box plot used to show?
Box plot for continuous data
- median = horizontal line in box
- upper quartile = top edge of the box
- lower quartile = lower edge of box
- Whisker length up to 1.5 times width of box
- Outliers shown as dots
Describe shapes of distribution.
What are the features of normal distribution?
- About 95% data lies within mean ± 2SD
- About 68% data lies within mean ± 1SD
- Used for ‘Normal ranges’, t-tests, 51 regression etc.
What are bar charts used to show?
- Shows frequency or percentage in each category
- May be quicker to absorb than a table
What are pie charts used to show?
Size of slice, defined by angle, proportional to frequency in category
how to find centre of distribution
positive skew/ negative skew = median
symmetrical = mean
out of RCT, case, cohort and cross sectional, which is interventional and which is observational?
RCT IS THE ONLY INTERVENTIONAL ONE, the rest is observational
