Understanding Jellyblubber Sampling: Methods & Findings

Names:____________________________________________________________ 1. Look at the Jellyblubbers colony. Pick out 10 Jellyblubbers that you think are a good representation of the entire population. Using the extra sheet, record the lengths of each of the Jellyblubbers that you picked in the table below. Jellyblubber Number Length Jellyblubber Number Length 22 5 mm 44 15 mm 17 5 mm 88 27 mm 64 8 mm 89 30 mm 68 13 mm 41 41 mm 39 15 mm 28 49 mm 2. What is the average length of the 10 Jellyblubbers from your sample above? 20.8 mm 3. In a few sentences, explain how you chose your Jellyblubbers. Would you consider this a simple random sample? Why or why not? I chose the Jellybubbers to represent the population based on their size. I used an eye test to try to group the jelly blubbers from smallest to largest. I wouldn’t consider this to be a random sample because I influenced the decision of which jelly blubber was chosen. 4. If you are doing this remotely, please use the attached Excel document or Google Sheet to randomly select 10 Jellyblubbers. If you are in class, Prof H will explain how to do this step. Jellyblubber Number Length Jellyblubber Number Length 88 27 mm 10 10 mm 39 15 mm 23 32 mm 32 20 mm 3 9 mm 79 17 mm 8 40 mm 33 43 mm 93 10 mm 5. What is the average length of the 10 Jellyblubbers from your sample above? 22.3 mm 6. Would you consider this a simple random sample? Why or why not?

This is a random sample since it was created using a random number generator. 7. If you are doing this remotely, you may skip this step. Otherwise, bring your results up to Prof H. Specifically, I need your answers to #2 and #5. 8. Suppose I didn’t have a random number generator and I was given the sheet of Jellyblubbers. To randomly pick 10 Jellyblubbers I blindly placed my finger somewhere on the sheet. If I landed on a Jellyblubber I recorded the Jellyblubber number and length. If I did not land on a Jellyblubber I did not record anything. I repeat this process until my finger has successfully landed on a Jellyblubber 10 times. Would you consider this a simple random sample? Why or why not? This wouldn’t be a random sample because the larger jellyblubbers have a higher probability of a finger landing on them due to their large area compared to the smaller ones. This means that the smaller jellyblubbers would have a disproportionate disadvantage compared to the larger ones in being chosen. 9. Identify the following for this survey. Population:___100____________________ Individual: 88, 39, 32, 79, 33, 10, 23, 3, 8, 93 Sample:________10__________________ 10. Record the mean of all of the values on the board for both C.S. and R.S. C.S. stands for convenience sample, R.S. stands for random sample. __23.7________ ___19.1_______ 𝑥 𝐶? ( ) = 𝑥 ?? ( ) = 11. The true mean length of all Jellyblubbers is 19.4 mm. Which value above is closer? Should our estimates be exact? Why or why not? What could we do to get closer to the exact value? The random sample is closer to the true mean length. The estimates aren’t expected to be exact due to sampling variability.To get closer to the exact value we could increase the sample size. 12. Look at the distribution of values for each sample that is greater than (highlighted) and less than 19.4 (the population mean). What do you notice about the sample means for the convenience samples? Why do you suppose that is that way? This means that the sample means for the convenience samples is likely to be higher than 19.4. The large jellyblubbers are easier to notice than the smaller ones meaning they could be overlooked when choosing a random sample by hand. This could lead to a higher length chosen due to more large jellyblubbers being chosen.

The JellyBlubber Colony Blubber # Length Blubber # Length 1 9 51 35 2 5 52 37 3 9 53 9 4 33 54 25 5 22 55 5 6 5 56 10 7 10 57 9 8 40 58 45 9 20 59 40 10 10 60 8 11 12 61 20 12 5 62 25 13 8 63 10 14 41 64 8 15 5 65 37 16 32 66 8 17 5 67 20 18 10 68 13 19 21 69 34 20 20 70 42 21 34 71 40 22 5 72 40 23 32 73 40 24 5 74 30 25 9 75 20 26 40 76 7 27 5 77 5 28 49 78 25 29 9 79 17 30 41 80 8 31 5 81 8 32 20 82 5 33 43 83 13 34 7 84 42 35 20 85 10 36 10 86 5 37 5 87 10 38 14 88 27 39 15 89 30 40 10 90 10 41 41 91 42 42 5 92 6 43 17 93 10 44 15 94 25 45 40 95 7 46 5 96 40 47 30 97 8 48 8 98 5 49 5 99 40 50 40 100 20

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The JellyBlubber Colony

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