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NZAMT NZQA NZ Grapher NZ Maths Census at School Study It

Population Inference

1.11 Bivariate Home | Assessment Criteria | Ask a Question | Make a Plan | Collecting Data | Cleaning Data | Making Scatterplots | Describing Scatterplots | Outliers | Line of Best Fit | Population Inference | Conclusion | Revision


Making a population inference - Conclusion

From the sample analysis we can make an inference about the population

Sample statistics may be of use: Mean Median, Mode, Minimum, Maximum

Making a conclusion based on the scatter plot and equation.

Answering our research question, with evidence. "I notice that..."

Population Inference Class notes, Blank notes

Writing a Conclusion Class notes, Blank notes

pg292, pg368

pg294 Ex18.02, pg370 Ex26.02



We use the sample statistics and graphs to make statements about the population.

We need to be aware that the sample will vary from the population

If the sample shows that there is a relationship between the two variables AND the sample size is reasonable (at least 30) then we can say there probably is a relationship in the population as well.

Remember the relationship can be…
Linear or Non Linear,             Positive or Negative,
Strong or Weak,                     with Constant Scatter or Non-Constant Scatter.

To ensure that a sample represents a population we need a sample size of at least 30


Calculating ‘Sample Statistics’ may be useful as well.

Use Excel to calculate the mean, median, mode, maximum, and minimum for the data.

You will have to calculate the sample statistics for EACH of the variables.

 =Average(click and drag over the data cells)
 =Median(click and drag over the data cells)
 =Mode(click and drag over the data cells)
 =Maximum(click and drag over the data cells)
 =Minimum(click and drag over the data cells)

=Range(click and drag over the data cells)
=Quartile(click and drag over the data cells,2)
=Quartile(click and drag over the data cells,4)

Inter quartile Range


In your conclusion you MUST refer back to your research question
To answer the research question use…
“I notice that…. “

Talk about :
The relationship (State the obvious “as height of students increases, arm span also increases) and Strong/Weak/Linear/Non-Linear/Constant Scatter /Non-Constant

The trend line (slope and equation) what it means and how well it represents the data (for all or part of the data range)

How the trend line can be used to make predictions and how appropriate these predictions are.

Any outliers or groups and what may have caused this.

The sample statistics referring to central tendency and spread

How well (or not) the sample represents the population.




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