Evaluating DataEvaluating Data

Is my data reliable?Is my data reliable?

Mrs Sharpe likes a nice piece of cod Mrs Sharpe likes a nice piece of cod from the fish shop.from the fish shop.

Two fishmongers ‘Fish R Us’ and Two fishmongers ‘Fish R Us’ and ‘Something Fishy’ have signs outside. ‘Something Fishy’ have signs outside. They both say; They both say;

Cod average length 30cm £2.50Cod average length 30cm £2.50 Mrs Sharpe buys one cod fillet each Mrs Sharpe buys one cod fillet each

week and measures them.week and measures them.

Fish R UsFish 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?

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

Yes the average length of a cod fillet is 30cm

Quite reliable the average is 30cm and the spread is only 1cm.

1 in 30 is quite small.

Something FishySomething 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?

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

Yes the average length of a cod fillet is 30cm

Not very reliable the average is 30cm but the spread is 10cm.

10 in 30 is a lot.

For Example:For Example:

Three pieces of data readThree pieces of data read5050 5252 4848

Work out the average and the spread.

How reliable do you think the data is?

Average =50 Spread = 2Average =50 Spread = 2

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

Another example:Another example:

Three pieces of data readThree pieces of data read100100 105105 9595

Work out the average and the spread.

How reliable do you think the data is?

Average =100 Spread = 5Average =100 Spread = 5

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

Another example:Another example:

Three pieces of data readThree pieces of data read8585 4040 8585

Work out the average and the spread.

How reliable do you think the data is?

Average =70 Spread = 22.5Average =70 Spread = 22.5

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