How do you analyse results with a graph and evaluate an investigation?
Analysing results: plotting and interpreting graphs, drawing a conclusion, and evaluating the reliability and validity of an investigation.
A concise overview of the analysis and evaluation skills for the WJEC GCSE Science Double Award practical assessment (Unit 7), covering plotting and interpreting graphs, drawing a conclusion, and evaluating reliability, accuracy and how to improve a method.
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What this dot point is asking
The WJEC Double Award practical assessment (Unit 7) and practical questions want you to analyse results with a graph, draw a conclusion, and evaluate the investigation.
Plotting a graph
Interpreting the graph and concluding
Read the graph to describe the relationship: for example "as the temperature increased, the rate increased", or note that the variables are proportional if the line is straight through the origin. Use the graph to find values, such as reading off the dependent variable for a given independent value.
Evaluating reliability and accuracy
Suggesting improvements
A good evaluation suggests how to improve the method, for example: take more repeats to make the mean more reliable, use a wider range of the independent variable, use more precise equipment, or control a variable more carefully. Improvements should be specific to the investigation, not just "be more careful".
Choosing the right type of graph
The type of graph depends on the data. A line graph is used when both variables are continuous (numbers that can take any value, such as temperature and rate). A bar chart is used when the independent variable is in categories (such as different metals or different materials). Choosing the correct type, and plotting it well, is part of analysing results. For continuous data, the line of best fit lets you see the trend and read off values; for categories, the bars let you compare. Picking the right graph for the data is a common skill tested in the assessment.
Conclusions and scientific knowledge
A strong conclusion does more than state the pattern: it explains the result using scientific knowledge. For example, "the rate increased with temperature because the particles moved faster and collided more often with enough energy (collision theory)". Linking the conclusion back to the relevant science shows understanding and gains extra marks. The conclusion should also say clearly whether the hypothesis was supported by the evidence, which closes the loop with the planning stage.
Try this
Q1. Which variable goes on the x-axis of a graph? [1 mark]
- Cue. The independent variable (the one you changed).
Q2. Give one way to make the mean of your results more reliable. [1 mark]
- Cue. Take more repeat readings (and ignore anomalies).
Exam-style practice questions
Practice questions written in the style of WJEC exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
WJEC style4 marksDescribe how to draw a good line graph of results, and how to use it to describe the relationship between two variables.Show worked answer →
A Unit 7 graph question worth 4 marks. Reward: choose sensible scales that use most of the grid, and label both axes with the quantity and unit (1); plot the points accurately and draw a line (or curve) of best fit (1); the independent variable goes on the x-axis and the dependent on the y-axis (1); describe the relationship by reading the graph, for example "as x increases, y increases" or that they are proportional if it is a straight line through the origin (1). Markers credit scales and labels, line of best fit, correct axes, and reading the relationship. A common error is to join the points dot-to-dot instead of a best-fit line.
WJEC style4 marksExplain how you would evaluate an investigation, referring to reliability, anomalies and improvements.Show worked answer →
A Unit 7 evaluate question worth 4 marks. Reward: comment on reliability - whether repeats agreed closely (1); identify any anomalous results and suggest why they happened (1); judge whether the method was valid (a fair test that answered the question) (1); and suggest improvements to the method, such as more repeats, a wider range, or more precise equipment (1). Markers credit reliability from repeats, anomalies, validity and improvements. A common error is to only say "it went well" without specific evaluation.
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