Suppose you believe that a specific type of plant will grow better in soil than in sand. You want to run an experiment to test your hypothesis.

Question

I could buy a sunflower seed packet from grocery outlet. I open the packet finding 10 sunflower seeds inside. I plant 4 sunflower seeds in 4 pots of soil and plant the other 2 sunflower seeds in 2 pots of sand. I also will water each plant every day and ensure each plant has the same amount of sunlight. Then I can measure the height of the sunflowers after one month.
What are the treatments in your experiment?
The treatment would be the soil or sand the plants grow in.

What is the response variable in your experiment?

The response variable in my experiment is the amount of plant growth

Where in your experiment would random selection occur?

Where in your experiment would random assignment occur?

Answer 1

In your experiment, random selection and random assignment are important concepts to ensure the validity of your results. Here’s how they apply to your scenario:

Random Selection:

In your current setup, you do not have a clear element of random selection because you are using all the seeds from a single packet. Random selection would typically involve choosing the seeds from a larger population in a manner that each seed has an equal chance of being selected. If you sourced your seeds from a larger batch or population of seeds or if you selected them randomly from a mix of seeds, that would be an example of random selection.

Random Assignment:

Random assignment involves assigning your selected individuals (in this case, the seeds) to different treatment groups in such a way that each seed has an equal chance of being placed in any group. In your experiment, you are planting 4 seeds in soil and 2 seeds in sand, which indicates a specific predetermined assignment rather than random assignment. To incorporate random assignment, you could randomly assign all 6 seeds to either the soil or sand pots (for example, using a method like flipping a coin or using random number generation) to eliminate any bias in the treatment assignment.

In summary:

• Random Selection: Not explicitly present in your current setup as you are using all seeds from a single packet. This could be incorporated if you sourced seeds from a larger population.
• Random Assignment: Currently not applied, as the assignment of seeds to treatment groups (soil vs. sand) is predetermined. You could enhance this by randomly assigning all seeds to either treatment group.