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Practical Skills and Data Analysis

Tables, graphs and presenting results

  • 3 things to know
  • Units AS 3 and A2 3

Overview

Recall questions on laying out raw and processed values in a table, which variable goes on each axis, choosing a scale and when a false origin is allowed, drawing a best-fit line, finding a gradient and its units, what an intercept means, the significance of an area under a curve, and how to treat an anomalous point.

What you need to know

Answer each one before you reveal it.

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Key term

Which variable is plotted on each axis of a graph of experimental results?

Key term

What makes a good choice of scale for a graph?

Key term

When is a false origin acceptable on a graph, and when must the axes start at zero?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    How should raw readings and processed values be arranged in a results table?

    Model answer

    Raw readings occupy the first columns exactly as they were taken, and each quantity calculated from them, such as a mean, a square or a reciprocal, is given a further column of its own with its own heading and unit.

  2. 2

    Which variable is plotted on each axis of a graph of experimental results?

    Model answer

    The independent variable, the one deliberately changed by the experimenter, goes on the horizontal axis and the dependent variable, the one measured in response, goes on the vertical axis.

  3. 3

    What makes a good choice of scale for a graph?

    Model answer

    The plotted points should occupy at least half of the grid in each direction, and each large square should represent a value such as 1, 2 or 5 units so that intermediate points can be plotted and read without awkward arithmetic.

  4. 4

    When is a false origin acceptable on a graph, and when must the axes start at zero?

    Model answer

    A false origin is acceptable, and often necessary, when the readings are clustered far from zero and the scale would otherwise be cramped, but the axes must start at zero whenever the intercept has to be read from the graph or whenever proportionality is being tested.

  5. 5

    How is a best-fit line drawn through a set of plotted points?

    Model answer

    It is drawn so that the points are distributed evenly above and below it along its whole length, with the line following the trend of the data rather than being forced through the origin or through any particular point.

  6. 6

    How should the gradient of a straight-line graph be determined?

    Model answer

    Choose two widely separated points that lie on the drawn line, not necessarily plotted data points, so that the triangle spans most of the line, and divide the change in the vertical quantity by the corresponding change in the horizontal quantity.

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