4.4 Designing Experiments to Reduce Variability
Reading Guide
Basics of a good experiment:
1.
__________________ assign one of _____________ treatments to each ____________________
2.
Handle them as __________ as possible except for _______________________.
If you can protect yourself against ________________ by randomizing, designing a good experiment becomes
mainly a matter of managing ________________________.
There are 2 types of variability in experiments:
1.
One type that you want because ______________________________________________
2.
One type that you don’t want because _______________________________________________
Differences Between Treatments Versus Variability Within Treatments
A Real Experiment: Kelly’s Hamsters
Average Enzyme Concentration for Long Days: _______
Average Enzyme Concentration for Short Days: _______
A Difference of: ____________
Variability within Short days (Range of Enzyme Concentration): _________
Variability with Long days (Range of Enzyme Concentration): ________
In order to conclude that the treatments make a difference, the difference __________ the treatments has to be
_____________ enough to overshadow the variation _______________ the treatment.
1
A Design for Every Purpose -- Activity 4.4a – Sit or Stand (will do in class) – fill in later
Part A – Completely Randomized Design -- Results
Side-by-Side Stemplots
Mean of Sitting Data: __________
Mean of Standing Data: ________
SD of Sitting Data: ________
SD of Standing Data: _________
Part B – Randomized Paired Comparison(Matched Pairs) -- Results
Difference = Standing-Sitting
Stemplot of Difference
Mean of Difference (Standing-Sitting): __________
SD of Difference: ________
Part C – Randomized Paired Comparison(Repeated Measures) -- Results
Difference = Standing-Sitting
Stemplot of Difference
Mean of Difference (Standing-Sitting): __________
SD of Difference: ________
2
Completely Randomized Design
In a completely randomized design, treatments are _____________________ to _______ without restriction. Use
a __________________________ to randomly assign a treatment to each experimental unit.
Steps in Creating a Completely Randomized Design (CRD)
1.
2.
The Randomized Paired Comparison Design
______________________ and ________________________ are examples of randomized paired comparison
designs.
Steps in Creating a Completely Randomized Paired Comparison (Matched Pairs) Design
1.
2.
In experiments of this type, the matched units or the individual units that receive all treatments in random order
are called __________________.
The Randomized Block Design
A randomized paired comparison design is a special type of _____________________________________. The
difference is that in a generalized block design more than _________________________________ may be in each
block.
Steps in Creating a Randomized Block Design
1.
2.
3
The effectiveness of blocking depends on _______________________________________ and how
___________________________________________________. The more _____________ the units within a block,
the ______________________ the blocking will be.
4