Your experimental design outlines a clear approach to testing your hypothesis about the growth of sunflowers in different types of substrates. Let me clarify the elements you've identified and provide some additional context:
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Treatments:
- The treatments in your experiment are indeed the two different growing conditions: soil and sand. This distinction allows you to compare how the same seeds perform in each environment.
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Response Variable:
- The response variable is correctly identified as the amount of plant growth, which you plan to measure using the height of the sunflowers after one month. This measurement will help you determine the effectiveness of each treatment.
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Random Selection:
- You mentioned that random selection occurs when the plants are chosen from the location you are getting your plants from. This is an important practice as it helps ensure that the seeds you are using are representative of the sunflower population. However, your description could be more explicit. Random selection typically refers to how you obtain your subjects; for example, if you randomly select seeds from a larger batch to minimize bias.
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Random Assignment:
- Your explanation of random assignment is good. It happens when you assign the selected seeds to either the soil or sand treatment. This could be accomplished, for instance, by randomly selecting which seeds go into which treatment group (e.g., using a random number generator or drawing lots). Random assignment helps to control for any potential biases and ensures that any differences in growth can be attributed to the type of substrate rather than inherent differences between the seeds.
In summary, your experiment is well-structured, and you've identified the key components correctly! To improve the rigor of your experiment, consider increasing the sample size if possible, as even a few more seeds could enhance the statistical validity of your findings.