Restraints

The Burning Question

Fixed or Random?

Facilities

Types of data.

Collection.

Measure or visual assess.

Time availability

Graduate students.

Short term grant.

Funding.

Never enough!

Factors and Factor Levels

Number of Factors

How many factors to include?

Often it is the more simple experiments that yield “best” results.

Two-way interactions can be difficult to interpret.

Generally include no more than 3 factors.

Number of Factor Levels

Explain the effect of increasing or decreasing levels.

• Usually only a few.

Predict values not included in actual study.

• Regression.

• Usually many factor levels.

Test different treatments to find “best”.

• Different insecticides, herbicides, etc.

• Determined by how many are available.

Fixed or Random?

Number of Factor Levels

Number of Replicates

The variation that is likely between factors and factor levels.

Degree of variability or heterogeneity over the experimental area.

Degree of precision required.

Precision

Number of

Replicates

Standard error of the

treatment mean

1 1.00

2 0.71

3 0.58

4 0.50

5 0.45

se[x] = /n

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1 3 5 7 9 11

13

15

17

19

21

23

se[m

ean

]

Number of Replicates

Precision

What is the magnitude of

difference that needs detecting?

Variance of plot = 2

sed[x] = 22/n

Differences 3 x sed[x] will be

significant at 5% level 5 times out of 6

Precision

What is the magnitude of

difference that needs detecting?

Variance of plot = 252 , n = 4

sed[x] = 2[5/2]=2.236

Differences 3 x 2.236 = 6.7 will be

significant at 5% level 5 times out of 6

Precision

In an experiment is 10% of the mean

(i.e. =m/10)

sed[x] = 2(m/10)2/4 = 0.07m

3 x 0.07 = 0.21

A true difference of 21% of the mean value will

be significant at the 5% level 5 times out of 6.

sed[x] = (m2/200)/ = 0.07m

Precision

To detect a true difference of 15% how

many reps would be needed?

sed[x] = 2(m/10)2/n

3 x 2(m/10)2/n < 0.15m

18 x (m2/102) /n < 0.152m2

n > [18 x (1/10)2/0.152 = 8

Precision

Plot Size

Bigger plots and more

replicates are always best.

Usually a compromise has to

be reached to fit restraints.

Machinery availability.

Physical yields.

Plot Size

Layout se[x] se[x] se[plot]

1 x 100 r/1 r1.00 p0.10

2 x 50 r/2 r0.71 p0.14

4 x 25 r/4 r0.50 p0.20

5 x 20 r/5 r0.45 p0.22

10 x 10 r/10 r0.32 p0.32

Machinery Available

On-farm Testing

Guard Rows and

Discard Rows

Mechanical damage usually occurs around the edges.

Avoid “edge effect”.

Guard rows can be used to “buffer” treatment effects.

Guard rows do not have to be the same species as is in trial.

Discard Rows

?

Examples

Jeannie’s Oriental Mustard

Oriental mustard (Brassica juncea

L.) is a new crop to the PNW

Growers have little experience

growing the crop.

Design an experiment to determine

the optimum growing conditions to

maximize productivity.

Four cultivars.

◦ 2 oilseed and 2 condiment.

2 planting dates.

3 seeding rates.

5 nitrogen levels.

3 Replicates.

Jeannie’s Oriental Mustard

Jeannie’s Oriental Mustard

9&10

7&8

5&6

3&4

1-2

Late Planting Early Planting

Jeannie’s Oriental Mustard

9&10

7&8

5&6

3&4

1-2

Late Planting Early Planting

I II III I II III

Jeannie’s Oriental Mustard

9&10 75lb 25lb 75lb 50lb 0lb 25lb

7&8 0lb 0lb 25lb 70lb 50lb 100lb

5&6 25lb 50lb 100lb 25lb 75lb 75lb

3&4 50lb 75lb 50lb 0lb 100lb 0lb

1-2 100lb 100lb 0lb 100lb 25lb 50lb

Late Planting Early Planting

I II III I II III

Jeannie’s Oriental Mustard

9&10 75lb 25lb 75lb 50lb 0lb 25lb

7&8 0lb 0lb 25lb 70lb 50lb 100lb

5&6 25lb 50lb 100lb 25lb 75lb 75lb

3&4 50lb 75lb 50lb 0lb 100lb 0lb

1-2 100lb 100lb 0lb 100lb 25lb 50lb

Late Planting Early Planting

I II III I II III

Jeannie’s Oriental Mustard

1

2

Ari

d 3

g

Ari

d 4

g

Ari

d 5

g

Jeannie’s Oriental Mustard

1

2

Ari

d 3

g

Ari

d 4

g

Ari

d 5

g

Am

ula

t 4 g

Am

ula

t 5

g

Am

ula

t 3 g

P. G

old

5 g

P. G

old

3 g

P. G

old

4 g

Ko

dia

k 5

g

Ko

dia

k 3

gK

od

iak 4

g

Jeannie’s Oriental Mustard

1

2

Ari

d 3

g

Ari

d 5

g

Ari

d 4

g

Jeannie’s Oriental Mustard

1

2

Ari

d 3

g

Am

ula

t 4 g

P. G

old

5 g

Ko

dia

k 5

g

Ko

dia

k 3

g

Ko

dia

k 4

g

P. G

old

4 g

P. G

old

3 g

Am

ula

t 5 g

Am

ula

t 3 g

Ari

d 5

g

Ari

d 4

g

Jeannie’s Oriental Mustard

Revision of

Experimental Design

and More Examples