Statistical tests and comparing variables

Decision on which statistical test to use for hypothesis testing depends on:Type of data (continuous or categorical)Whether the groups are independent or pairedWhether the data is normally distributed or notNumber of groups CONTINUOUS OUTCOMES Paired groups:Repeated data on the same groups of patients e.g. before & after intervention CATEGORICAL OUTCOMES E.g. percentages or proportionsWill usually … Continue reading Statistical tests and comparing variables

Statistics in Clinical Trials/Metanalysis

Sample size calculations Sample size calculations need to be done before data collectionSample size calculations are done in a statistics packageFactors that influence sample size calculation:Expected effect size - if expected effect size is ↑, can have ↓ sample size to detect differenceExpected variability (SD) of data - look at previous trials for approximationSignificance level … Continue reading Statistics in Clinical Trials/Metanalysis

Observational Studies/Epidemiology

Observational studies include: cohort; case-control; and cross sectional studiesThey are non-randomised & non-experimental Cohort studyProspective Used to determine aetiology & natural history of diseaseDefine cohort --> assess risk factors to follow --> follow forward in timeUsed to calculate risk ratioRisk ratio indicates increased/decreased risk of disease associated with factor of interest AdvantagesDisadvantagesTime sequence can be reviewedCostly Provides … Continue reading Observational Studies/Epidemiology

Clinical Trials/Ethics

Clinical Trials Interventional/experimental trialsUsually include randomisationThey are prospective (individuals are followed forward from some point in time)Causal analysis – test causal relationship between exposure of interest & outcome Phases of clinical trials Translational pathway of clinical trials:  Pre-clinical trials:Before testing in humansHelps decide whether the drug is ready for clinical trials (from ‘bench to bedside’)Look … Continue reading Clinical Trials/Ethics

Types of Data and summarising Data

Types of Data Types of data include:Non-numerical/qualitative/categoricalWhen a variable/observation can only belong to a distinct categoryIncludes nominal & ordinal NominalUnordered & mutually exclusive categories. Not possible to rank Examples – alive/dead, blood groupOrdinalOrdered  & mutually exclusive categories. Can be ranked. Difference or ‘gap’ between values can be ill-defined, Examples – mild/moderate/severe Numerical/quantitativeWhen a variable/observation takes … Continue reading Types of Data and summarising Data

Normal and non-normal distributions

Normal/gaussian distributionsThe mean is the peak of curve – it is symmetrical around its meanThe standard deviation determines width of curve (the larger the SD, the wider the curve)Normal distribution tends towards infinity (i.e. the line never reaches the axis)Reference range for a sample = mean +/- 2 standard deviation Non-normal distribution/skewness: NEGATIVE SKEW or … Continue reading Normal and non-normal distributions