Cambridge International Mathematics

For randomly scatteredpoints with no upward or

downward trend, we say there isno correlation.

Step 2: Look at the spread of points to make a judgement about thestrengthof the correlation. For

positive relationshipswe would classify the following scatter diagrams as:

We classify the strengths fornegative relationshipsin the same way:

Step 3: Look at the pattern of points to see if the relationship islinear.

The relationship is approximately linear. The relationship is not linear.

In the scatter diagram for theOpening Problemdata, there appears to be a moderate positive correlation

between the footballers’ heights and weights. The relationship appears to be linear.

EXERCISE 22A

1 For each of the scatter diagrams below state:

i whether there is positive, negative, or no association between the variables

ii whether the relationship between the variables appears to be linear

iii the strength of the association (zero, weak, moderate or strong).

abc

strong moderate weak

strong moderate weak

y

x

y

x

y

x

Two variable analysis (Chapter 22) 457

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Y:\HAESE\IGCSE01\IG01_22\457IGCSE01_22.CDR Monday, 27 October 2008 2:14:38 PM PETER