is the inner logic of an analytical study design. A study follows a forward directionality when first the exposure groups are defined based on the study factor and then the participants are followed-up to detect the outcome. Studies of “backward” directionality first define groups based on the outcome and then look backwards to exposure status of p [..]

are biological, physical, or chemical factors that contribute to the occurrence of a disease. Biological agents such as viruses and bacteria are often necessary causes for (infectious) diseases. Chemical agents such as poisons or allergens, or physical agents such as radiation, noise, or heat, are all non-biological agents that are frequently not n [..]

is one of the two types of potential errors when conducting a statistical hypothesis test. An alpha error can only occur when the statistical test result is ‘significant’ (i.e. p<0.05). In this case, there is still a small chance (below 5%) that the observed difference (or the observed amount of association) is attributable to chance alone and d [..]

is a quantitative, comparative study investigating the relationship between a study factor and an outcome. Analytical studies often assess the effect of potential causes of disease, pathogenic mechanisms, risk factors, prognostic factors, or remedial therapies. The crucial features of analytical research are the inclusion of a control group (agains [..]

is a measure of association in cohort studies and experimental studies. The attributable risk is a difference measure and calculated as the difference between the incidence of the outcome in the exposed group (or intervention) and the incidence of the outcome in the unexposed group (or control). Bar Chart (univariate) -is usually a graphical displa [..]

is also used as a name for type of bivariate graphical display where one categorical and one numerical variable are involved. In a bivariate barchart, usually the means (sometimes also other measures of central tendencies) of the numerical variable within the different categories of the categorical variable are displayed as disjointed rectangles or [..]

is the average number of people directly infected by an infectious case during its infectious period, when the case enters a completely susceptible population. The basic reproductive rate is the theoretical potential of an infection to spread in an entirely susceptible population. Beta error (Type II error) – is one of the two types of potential er [..]

an adjective used in statistics to describe situations or procedures where two different variables are considered or involved.

is a design feature of experimental studies. An experiment is called (single) blind, if either the participants or the investigator who administers the intervention or the investigator who assesses the outcome (if applicable) do not know whether the individual patient has been allocated to the intervention group or the control group. An experiment [..]

is a bivariate graphical display of the values of a numerical variable in the categories of a categorical variable. For each category, the numerical values are displayed using five values: the minimum, the 25% quantile, the median (50% quantile), the 75% quantile and the maximum. Often the interquartile range is depicted as a box with the median ma [..]