1. Experimental design

2. #1 #2 Independent measures control 20 cows
Measure weight
Measure milk yield #2
control
I’m a farmer and I want to test two different types of cow supplement to see which one is best,
supplement #1 or supplement #2
I have 60 cows. I run the experiment for 2 weeks and then record the data

3. #1 #2 Independent measures control
20 cows
Measure weight
Measure milk yield #2
control
+15%
Each cow is only tested in one condition It’s quick easy and if the results are clear they can be easily seen. Can I be sure all three groups were equal at the start of the experiment? Was one group naturally stronger?
+5%
-2%

4. Repeated measures
Normal farm running
All cows
Measure weight
Measure milk yield #1
All cows for 2 weeks #2
Each cow is tested in all three conditions It’s takes longer but my data is less likely to be skewed by uneven groups. Can I be sure the order I performed the conditions hasn’t influenced the result? Would the results be the same if I reversed the conditions?
To get a baseline reading
+9%
+6%
and then