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Example 6 - Bar chart

Study the bar chart below and answer the questions that follow. Once you have entered your thoughts in the box provided click on the 'Check your answer' button to see a suggested answer.

Figure 6: Effect of DMSO concentration on cell viability in 2 plant cell lines, wheat (Triticum monococcum L.) and maize (Zea mays L.). Both cell lines were treated with 0% or 5% DMSO for 24 hours and then harvested. Cell viability was measured by staining with BRDU and then analysed by flow cytometry. Results are presented as the average of triplicate experiments.

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Questions:

1. Are appropriate numerical scales used for the X and Y axis?
2. Are all the axes sufficiently labelled?
3. Are error bars necessary?
4. Does the figure legend contain sufficient detail to make the figure "stand-alone"?
5. Is this the best format in which to present the data?

Appropriate numerical scales are used and the X and Y axes are sufficiently labelled. However, the bar chart does not include a key and therefore it is impossible to know which bars represent the wheat cell line and which bar represents the maize cell line. Furthermore, the Y-axis label is aligned horizontal to the axis. Y-labels are usually written vertically along the axis.

Error bars are necessary and should be included as the data presented is the average of triplicate experiments.

The legend includes a number, title, and a brief description of how the data were collected and analysed. This is a good legend which contains sufficient details of methodology and is concisely written without superfluous text. However, the concentration of BRDU used is omitted. It is important that quantitative aspects of the method are included and therefore this information should be added to the legend.

The format of the bar chart is very poor. The bars are in 3D and background colour and grid lines are used. Remember, each figure should be presented simply and clearly so that the data can be interpreted efficiently. This is clearly not the case for this particular bar chart.

The figure could be re-designed and presented as below. If you study the improved figure, you will note that the bars are now presented in 1D and the background and grid lines have been removed. This makes data interpretation much easier. In addition, a key has been added in the body of the figure and error bars have been added to each data bar.

Figure 6: Effect of DMSO concentration on cell viability in 2 plant cell lines, wheat (Triticum monococcum L.) and maize (Zea mays L.). Both cell lines were treated with 0% or 5% DMSO for 24 hours and then harvested. Cell viability was measured by staining with BRDU (30μM) and then analysing by flow cytometry. Results are presented as the average of triplicate experiments (± SEM).

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