The correct answer is b). A bar chart is a very simple graph to construct which allows you to display the frequency counts or the percentages of a categorical variable. It is the most effective way to compare frequency counts or percentages graphically. In a bar chart, the horizontal axis represents the levels or categories of the variable of interest (categorical), while the vertical axis represents the frequency counts or the percentages. The special feature of this graph is that there is always a gap between the bars

 The correct answer is d). The most common form of a histogram is obtained by splitting the range of the data into equal-sized intervals or bins (i.e. classes). In a histogram, the horizontal axis represents the bins of the variable of interest (continuous), while the vertical axis represents the frequency (i.e. counts for each bin). The number of bins used is important; generally between 5 and 15 classes should be used. This graph is a very useful tool for spotting outliers or potential errors in a dataset and visualising the distribution of the variable of interest. The special feature of this graph is that there is no gap between the bars

 The correct answer is c). Alongside a histogram, a dot plot is an alternative way to display the distribution of a continuous variable. It can also be used to compare a continuous variable between groups. It plots one point for every observation, with similar values placed next to each other. It is also good at shows outliers or extreme values. This type of plot is impractical when there are too many observations as the points will be stuck to each other. The special feature of this graph is that it is constructed with dots, allowing you to identify each individual observation.

 The correct answer is a). A pie chart is built up from a number of wedges that are each used to illustrate the percentage of observations in one category. The size of the angle for each wedge at the centre of the pie indicates the proportion of subjects within the corresponding category with respect to the whole sample size. The bigger the angle of the wedge, the larger the proportion of subjects in the category. The special feature of this graph is very obvious; it looks like a round cake or pizza. If there are too many categories it can be difficult to understand data in the chart.

 The correct answers are b), d) and f). Age, Height and LDL are continuous variables and a histogram is an effective graph to illustrate the distribution of the variables.

 The correct answers are c), e), g), h), i) and j). They are categorical variables, and a bar chart is an effective graph to illustrate either the frequency or percentage (or proportion) of each category for this type of variable.

 The correct answer is k). This chart is generated when the individual values of a continuous variable are plotted as bars. It is not a histogram but could be considered as a bar chart if you had a categorical variable with numerous categories. If you ticked Gender, Blood group, Feeling happy, Number of child, Smoke and Social Class then this is acceptable.

 The correct answers are b), d) and f). Age, Height and LDL are continuous variables and a box plot is an effective graph to illustrate the distribution of each of these variables, though a histogram may reveal more information.

 The correct answers are c), e), g), h), i) and j). Gender, Blood group, Feeling happy, Number of child, Smoke or Social Class are categorical variables, a pie chart may be used to illustrate either percentage (or proportion) of each category for this type of variable, though a bar chart is often preferred. Pie charts are rarely found in journal publications, but appear in presentations or posters.

 The correct answers are b), d) and f). Age, Height and LDL are continuous variables and a dot plot may be used to illustrate the distribution of each of these variables, though a histogram is more frequently encountered.