Using Tables and Graphs to Evaluate Data

8/11/2019 Using Tables and Graphs to Evaluate Data

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Is it valid?

Datais only valid for use in coming to a conclusion ifthe measurements taken are affected by a

single independent variable only

A guide to writing up experiments


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Biotic indicators

A biotic indicator is a species used to monitorthe health of an environment or ecosystem.

Cress is grown

on cotton woolsoaked in liquidsof different pH.

After so manydays, itsheight is

measured


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Prediction What factors do you think affect the

growth of cress seedlings?

How do you think pH will affect theheight of the plants after 5 days?


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pH

Measurement of cress seeds (cm)

1 2 3 4 5 6 7 8 9 10 Mean

4 1 0 0 0 0 0 0 0 0 0 0.1

5 2 1 2 1.5 1.5 1 4 0 0 0 1.2

6 0.8 1.6 1.1 1.1 0 0 0 0 0 0 0.46

7 5 2.5 4 1 0 0 0 0 0 0 1.25

8 0.5 0.4 0.2 0 0 0 0 0 0 0 0.11

9 0 0 0 0 0 0 0 0 0 0 0

Cress seeds are grown on cotton wool soaked in liquids of different pH

What is wrong with this table?What sort of graph should we plot?Was height the best thing to measure?

Were the seeds left for long enough?


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The Students Graph

pH of liquid used to moisten cress seeds

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 1 2 3 4 5 6 7 8 9 10

pH

cm

Why is there a big drop at pH 6?Is it a large drop?What does the graph not show?

What is good about this graph?

What is bad about this graph?


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The Students Analysis:

Up to 6, the pH helps the cress plantsto grow

How much informationdoes this analysisgive?

In your pairs, come upwith a better one

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 1 2 3 4 5 6 7 8 9 10

cms

pH

pH of liquid used to moisten cress seeds


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The Students Evaluation:

My experiment went well, I got the results Iexpected

How much information does this Evaluation give?

In your pairs, come up with a better one


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wwwI did lots of repeats to make sure that I couldignore any anomalous results

The experiment was valid because there was only one

independent variable, the pH and everything else, likethe light and temperature was controlled.

I used the same number of seeds and volume of solutionin each test so that it was fair.

Ebi: I only looked at the height of the cress seedlings. Icould have measured the width and colour of the leavesas well.

The heights were all very small, so if I measured them

over a period of several weeks, I could see if the pHaffected the growth over a period of time.I could also have seen if pH slowed down germination,rather than stopped it.

I could have made it more accurate by using verniercalipers to measure the height of the seedlings.

Comment onreliability

Comment onValidityand fairtesting

Improvementfor getting moredata

Improvementfor getting

better data

Improvementfor greateraccuracy


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Measuring Heights in a Class The teacher asked her

pupils to measure their

heights and show thedistribution of heights in theclass in a table and a graph.

What prediction can youmake?


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Students results table

Number of pupils Height in cm2 160

4 165

7 1706 175

4 180

1 185

There is a basic error in this table. What is it?How could the results be made clearer?


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Students results table

Height range/cm Number of studentsin that range

160-164 2

165-169 4170-174 7

175-179 6

180-184 4

185-189 1

ebi percentages shown


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The Students graph

Is this the best way to display the results?How can we make the graph clearer?

Heights are continuous, so why is a line graph inappropriate here?


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Analysis and EvaluationThe greater the number of pupils the

more the height changes

Write a better analysis!

Try writing an evaluation with wwwand ebi.


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Measuring current in wires of

different lengths The teacher asked her

pupils to measure the

relationship between currentand the length of a wire.

What were the controlvariables?

What would you predict?


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Measuring current in wires of different lengths

Length of

wire (cm)

Current (amps)

1 2 Average

5 3.55 3.54 3.545

10 3.50 3.49 3.495

15 3.09 3.07 3.08

20 2.65 2.63 2.64

25 1.76 1.73 1.745

30 1.57 1.59 1.58

Are the results consistent?Are the results reliable?How can we ensure the results are reliable?


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Current and length of wire

0

0.5

1

1.5

2

2.5

3

3.5

4

0 5 10 15 20 25 30 35

length in cms

amp

What sloppy mistakes have been made?Is it sufficient to use the average?Why isnt the relationship a straight line?


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Conclusion

The longer the wire the less of thevalue of the current




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Measuring ground coverage in a lawn

The teacher asked herpupils to work out the

ground coverage of variousplants in a lawn.

What were the controlvariables?


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Estimating ground coverage of lawn by science block

Plant Group 1 Group 2 Group 3 Group 4 Average %

Clovers % 25 0 0 0 6.25

Grasses % 50 15 10 50 31.25

Leaves % 25 50 50 20 36.25

Barleygrass %

0 25 5 5 8.75

Thistles % 0 1 0 0 0.25

Thorns % 0 0 5 0 1.25

Weeds % 0 0 0 10 2.5

Soil % 0 9 30 9 12

Is this evidence valid?Is it accurate?

Is the average meaningful?


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Distribution of plant coverage of the school grounds

05

1015

2025303540

Clovers Leaves Grass Barley

grass

Thistles Thorns Weeds Soil

Plants on grassy area by science block

%

Is this the best way of showing this information?

Is this valid for the whole school grounds?

Is the independent variable continuous or discontinuous?


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Conclusion

The plants with the biggest leaf areascovered the most ground



R lli d d i d


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Rolling a car down a ramp and measuring speedat a fixed point.

Height of ramp (cm) Speed (m/s)

5 1.2

10 1.5

15 0.7

20 2.125 2.4

30 2.7

35 3.0

40 3.3

How can the data be made more reliable?

Are there any anomalies?What variables need to be controlled?


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Speeds reached

0

0.5

1

1.5

2

2.5

3

3.5

5 cm

10cm

15cm

20cm

25cm

30cm

35cm

40cm

How can the results be showed more clearly?What other improvements are needed?


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Conclusion

The speed of the car always increasesif the ramp is made higher



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Using Tables and Graphs to Evaluate Data