Quantitative Flashcards
Define an observational study.
A study that does not include an intervention or experiment, only observation of natural relationships between factors and outcomes.
What are some types of observational studies?
cross-sectional, longitudinal, case-control, cohort and survey studies.
Describe a cross-sectional study.
A study that looks at a cohort at a single point in time.
Describe a longitudinal study.
A study that uses repeated measures over a long period of time.
Describe a case-control study.
A study that looks at the relationship of an outcome (case) versus no outcome (controls) and compares this to previous exposures. Also known as a ‘retrospective study’.
Describe a cohort study.
Almost the opposite to a case-control study. A study that follows a population with exposure to identify whether an outcome is developed or not.
Describe a survey study.
A study that uses surveys to collect data from participants. Particularly useful for collecting data from a geographically widespread population.
Define an interventional study.
A study that employs manipulation of a variable to define the outcome of this intervention on a specific population. Also known as experimental studies.
What are some types of interventional studies?
randomised control trials, pre-post studies, and non-randomised control trials.
Describe a randomised control trial.
A trial where subjects are randomly assigned to one of two (or more) groups- either the experimental or the control group. The outcomes of both groups are then compared.
What are some features of a well-designed RCT?
a large enough sample to allow generalisation of results
concealed randomisation of the subjects to each group
both groups are treated identically by researchers
analysis is focused on the research question
Describe a pre-post study.
A study that measures the occurrence of an outcome before and again after a particular intervention is implemented.
Why is a pre-post study not as strong as an RCT?
They suffer poor internal validity because they cannot accurately control for every variable that may be responsible for the outcome of an intervention like an RCT can.
Describe a non-randomised trial.
Similar to an RCT where there is an intervention and control group however there is no randomisation of participants into these groups.
Why is a non-randomised trial not considered a strong study design?
They can suffer from bias.
What is a variable?
an attribute that varies or changes between individuals, objects, qualities, and properties.
What are some different types of variables?
numeric (discrete or continuous), categorical (nominal or ordinal).
What is a numeric variable?
a variable that has a measurable value described by a number
What is the difference between a discrete and continuous variable?
a discrete variable uses only whole numbers (i.e. 1 child) whereas continuous can use values between units (i.e. 55.4kg).
What is a categorical variable?
A variable that may be divided into groups (i.e. race, sex, age group).
What is the difference between a nominal and an ordinal variable?
nominal variables have no natural order (i.e. gender), whereas ordinal variables are able to be ordered (i.e. satisfaction of treatment is 1=not satisfied, 2= slightly satisfied 3= moderately satisfied & 4= very satisified).
What is the difference between an interval scale and a ratio scale?
A ratio scale uses a true-zero point (i.e. weight, height) whereas an interval scale uses an arbitory zero point (i.e. temperature).
When might we see a bimodal distribution of data on a histogram?
When there are two distributions mixed together, i.e. heights of males and females on the same histogram.
When the distribution of data on a histogram is skewed, which direction do we name this for?
towards the tail, so a distribution with a tail to the right will be skewed to the right or positively skewed
When would we use a denisty plot over a histogram to visualise data?
When we need a better understanding of the data density. Histograms can vary in their picture depending on how many ‘bins’ are chosen.
It is also possible to overlay density plots making comparing of two data groups possible.
When might histograms be chosen over density plots?
If visualisation of data must be done by hand, density plots are difficult to draw and need software to be produced.
What is the difference between mean and median?
The mean is the average of a data set whereas the median is the middle figure in the data set.
What is the median also known as?
the 50th percentile or the 0.5 quantile