Experimental design

Experimental design and stats

1. Principles of Experimental Design Presented By : Rana Asif Abbas Presented to: Dr Fahid Wattoo Course: PBG-507

2. Presentation outline :

3. Definition of experimental design

4. Applications of experimental design The methods of experimental design are widely used in following fields

5. History of experimental design James Lind performed wee organize experiment in 1747 and developed a cure for scurvy. His experiment miss only randomization. Ronald fisher present methodology for designing experiment in his books His work fall under the first era(1918-1940) of design of experiment.

6. Why we need experimental design From a statisticians perspective experiment is performed to decide: Weather there is actual difference among treatments and it is not due to difference in experimental units. Secondly wot is the size of difference among treatments But there is not always such ideal conditions that there is no variation among experimental units. So due to difference among experimental units, variation between treatments is caused other than actual difference need to be tested.

7. In simple words We need experimental design to control variability caused by other factors. So that the treatment effect can be identified prominently and accurately. Technically experimental design are for reduction of experimental error (The difference among experimental plots treated alike is called experimental error If experimental error is more , it mean the basic variation among treatment is due to chance. If experimental error is less it mean there is differ

8. Example Suppose there are two experimental plots x&y. A rice breeder has to do experiment to check the yield of two new varieties(A & B) he made. He sow variety A in X plot while variety B in Y plot. The results he got from this simple experiment are sure not be accurate. This is because along with the variety difference(treatment difference) , there are many other differences in plots like soil condition, moisture, sunlight etc. Even if he plant same variety A in plot x & Y he will get different results(experimental error) Breeder will follow principles of experimental design and design a suitable experiment for proper evaluation.

9. Principles of experimental design

10. Replication Reptation of basic experiment is called replication. Helps in getting more accurate estimate of experiment error. More replication means more precision. Replication reduce standard error. Example: Rice breeder, planted his variety A and B in more than one experimental units. The more number of time he plant any variety in experimental unit the more replication it would be.   Variety A Variety B Replication 1 Plot 1 Plot 5 Replication 2 Plot 2 Plot 6 Replication 3 Plot 3 Plot 7 Replication 4 Plot 4 Plot 8 n=r= No of replications One Plots= one experimental unit

11. Randomization It is process of assigning the treatment to experimental units Each treatment has same probability to get a experimental unit. If treatments 3 (A,B,C) and replications 4 than no of experimental units = 12 . A C B C C B A B A C B A

12. Example   Treatment Treatment Replication 1 Plot 1(A) Plot 5(B) Replication 2 Plot 2(A) Plot 6(B) Replication 3 Plot 3(A) Plot 7(B) Replication 4 Plot 4(A) Plot 8(B) Rice breeder having two treatments(variety A & B). Number of replications =4 Number of experimental units(plots)=8 The non-random layout is: There is chance for fertility gradient or any other biasness from one direction to other. Breeder follows any randomization method and have following layout. B A A B A B B A

13. Methods to do randomization By Cards

14. By Random number table Random number Sequence Rank 204 1 3 279 2 4 711 3 6 100 4 1 197 5 2 619 6 5 889 7 8 787 8 7 Assign the plot number from 1 -8. Open random number table and move finger any where from left to right with eyes close. Stop any where and select a three-digit number and move vertically to took 8 numbers. Write sequence of random numbers and rank from smallest to largest. Plot no Variety Sequence 1 A 1 2 A 2 3 A 3 4 A 4 5 B 5 6 B 6 7 B 7 8 B 8

15. Now assign the 8 treatments to 8 plots by seeing sequence corresponding to rank. E.g: The treatment A with sequence 1 will assigned to plot 3 because its rank is 3 Plot 1(A) Plot 5(B) Plot 2(B) Plot 6(A) Plot 3 (A) Plot 7(B) Plot 4(A) Plot 8(B)

16. Local control Choose a design in such a manner that all extraneous sources of variation are brought under control

17. Blocking Arrangement of experimental units into blocks of similar entities is called as blocking. Blocking means that the like experimental units should be collected together to far relatively homogeneous groups. Observations collected under similar experimental conditions are grouped in the same block. Blocking reduces sources of deviations and thereby bringing more precision to the experimental design.

18. Balancing Balancing means that the treatment should be assigned to the experimental units in such a way that the result is a balanced arrangement of treatment.

19. Proper plot technique Plot with homogenous soil Equal slope Equal block size and shape Equal number of replications Removal of border plants Thinning Furrowing for row spacing Fertilizer application Labeling Pesticide application