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Scientific Enquiry - Evaluating Evidence

Grade 6Cambridge (IGCSE)

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Evaluating evidence involves checking the reliability of data. Data is considered reliable if repeating the experiment yields similar results.

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An anomalous result (or outlier) is a data point that does not fit the overall pattern or trend. These are often caused by human error or equipment malfunction and should be identified before calculating a mean.

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A trend or pattern describes the relationship between variables. For example, 'As the temperature increases to 50∘C50 ^\circ C, the rate of reaction also increases.'

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To ensure a fair test, only the independent variable is changed. If other variables are not controlled, the evidence is not valid and cannot be used to draw a firm conclusion.

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Comparing a prediction to the actual evidence: If the data matches the prediction, the hypothesis is supported. If not, the hypothesis may need to be modified or rejected.

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The mean (average) is used to reduce the effect of random errors. The formula used is xˉ=∑xn\bar{x} = \frac{\sum x}{n}, where ∑x\sum x is the sum of values and nn is the count.

📐Formulae

Mean=Sum of all valuesNumber of values\text{Mean} = \frac{\text{Sum of all values}}{\text{Number of values}}

Range=Maximum value−Minimum value\text{Range} = \text{Maximum value} - \text{Minimum value}

💡Examples

Problem 1:

A student measures the distance a toy car travels in 33 trials: 1.2 m1.2\text{ m}, 1.3 m1.3\text{ m}, and 2.9 m2.9\text{ m}. Identify the anomalous result and calculate the mean of the reliable evidence.

Solution:

Anomalous result: 2.9 m2.9\text{ m}. \nMean = 1.2 m+1.3 m2=1.25 m\frac{1.2\text{ m} + 1.3\text{ m}}{2} = 1.25\text{ m}.

Explanation:

The value 2.9 m2.9\text{ m} is significantly different from the other two results, suggesting an error occurred during that trial. It is excluded from the mean calculation to ensure the final evidence is more accurate.

Problem 2:

In an experiment testing how H2OH_2O temperature affects salt solubility, a student predicts: 'Higher temperatures will allow more salt to dissolve.' Their results show: 20∘C=35 g20 ^\circ C = 35\text{ g}, 40∘C=37 g40 ^\circ C = 37\text{ g}, 60∘C=40 g60 ^\circ C = 40\text{ g}. Does the evidence support the prediction?

Solution:

Yes, the evidence supports the prediction.

Explanation:

The data shows a clear positive trend. As the temperature increases from 20∘C20 ^\circ C to 60∘C60 ^\circ C, the mass of dissolved salt increases from 35 g35\text{ g} to 40 g40\text{ g}, which matches the student's prediction.