Needle Length in Conifers (1B)

 Questions:

1. In comparing your histogram to the description of a normal distribution, did you seem to get a fairly good fit to the bell-shaped curve, or did you notice a different pattern? Describe these differences: was the histogram bimodal? Skewed? Flattened or sharply peaked? If you performed statistical tests using these data, would you be comfortable using parametric statistics, or would you seek a non-parametric alternative? Do you think you made enough measurements to make a certain judgment on this question, or for you think more data may be needed?
   •  The histogram did not fit the bell-shaped curve very well; it was more skewed than anything, but still did not fit that description well. It was somewhat flat, with a very high peak at the 22.0-22.5 cm range, which is the middle point. I don't think I would be very comfortable using parametric statistics because most of the data falls to the right of the peak, with only 19 needles (less than 25%) shorter than 22.0 cm. I feel as though I made enough measurements, especially when comparing my data to information available about needle length for this species of tree.
2. The mean, median, and mode are three different statistical approaches to describe the “typical” individual in a population. Based on your data, does it matter very much which of these three statistics is used? Explain how this answer is related to your answer for the previous question.
   • Between mean (23.6 cm) and median (23.8 cm), it matters little which is used; they are only a fifth of an inch apart. However, the mode (26 cm) is significantly larger than both numbers. This relates to question one because it shows that the data does not fall in a bell shape.
3. What do the variance, S.E., or standard deviation estimates tell you about your population that the mean does not tell you? Why is it important to report some measure of variation, along with the sample size, whenever you report a calculated mean?
   • The standard deviation estimates tell us the range of the needles lengths, whereas the mean only tells us the average needle length. It is important to report variation and sample size because it gives the reader a general idea of the different needle lengths and can help them determine how accurate the data collected is.
4. How would you design experiments to determine the importance of this trait in determining survival and reproduction? How would you test the extent to which this trait is heritable?
   • The needles/leaves of trees are very important for survival because they aid in the creation of energy. I would test the importance of needle length on survival by measuring needle lengths from many trees of the same age and seeing if height and girth relate. I am assuming that the bigger a tree, the better fit it is. I would test its significance to reproduction by measuring the amount of seeds produced from trees of the same age compared to the length of the needles. I would be assuming that the trees I am experimenting on are at a reproductive age, and that the same percentage of seeds from each tree will be fertilized and will grow into a new tree. I would test how heritable the trait is by planting seeds from trees of the same age with different needle lengths and seeing how long the needles of the offspring grow to be.
   
   
   
    **Aidan Bailey and Lauren Ali worked with me.