Evaluating Data

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Evaluating Data
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Is my data reliable?

• Mrs Sharpe likes a nice piece of cod from the
  fish shop.
• Two fishmongers Fish R Us and Something Fishy
  have signs outside. They both say
• Cod average length 30cm 2.50
• Mrs Sharpe buys one cod fillet each week and
  measures them.

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Fish R Us

• Length of cod fillet in cm
• Week 1 29cm Week 2 30cm Week 3 31cm
  Average length 30cm

• Is the advert for cod fillets 30cm true?

Yes the average length of a cod fillet is 30cm

• How reliable are Fish R Us? Are the fish all
  about 30cm long?

Quite reliable the average is 30cm and the spread
is only 1cm. 1 in 30 is quite small.
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Something Fishy

• Length of cod fillet in cm
• Week 1 30cm Week 2 20cm Week 3 40cm
  Average length 30cm

• Is the advert for cod fillets 30cm true?

Yes the average length of a cod fillet is 30cm

• How reliable are Something Fishy? Are the fish
  all about 30cm long?

Not very reliable the average is 30cm but the
spread is 10cm. 10 in 30 is a lot.
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For Example
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Three pieces of data read50 52 48
Work out the average and the spread.
How reliable do you think the data is?
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Average 50 Spread 2

• The data is fairly reliable as 2 in 50 is quite
  small.

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Another example
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Three pieces of data read100 105 95
Work out the average and the spread.
How reliable do you think the data is?
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Average 100 Spread 5

• The data is fairly reliable as 5 in 100 is quite
  small.

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Another example
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Three pieces of data read85 40 85
Work out the average and the spread.
How reliable do you think the data is?
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Average 70 Spread 22.5

• The data is unreliable as 22.5 in 70 is a lot.