Scatter graphs.
Line graphs may be used at a later stage when there is a better idea of the general shape of the line - whether it is a straight line, a quadratic curve, a logarithmic or exponential curve etc, or one of the standard probability distributions.
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Only if they are badly presented graphs or if the person viewing them is not a visual person.
Tables and graphs are used to present data in an easier to view and analyze format.
Many people find it easier to take in information when it is presented in visual form. Graphs and charts are often not much use for the actual analyses but may help suggest the sort of analyses that should be carried out.
In a graph
There is no one way of presenting data. There are good ways and there are bad ways. You must consider the nature of the data to decide the best way of presenting it. Consider that the famous nurse Florence Nightingale is credited with the first use of "pie charts" to illustrate medical data to non-medical persons. Human beings are very "visual" in nature, so choose the way of presenting data that gives the best impression of the principle you are trying to convey. Pie charts are best for presenting percentages, while line graphs are best for presenting trends, while raw numerical data may be best presented in a table with one quantity ascending/descending in value in the leftmost column. If using computer software such as Excel to present data, you will find a number of choices available in the Chart Wizard which allow you to provide the best visualization.