KIWI Class Notes 2021
JUNIOR REPORT IN BOLD TYPE
Before you start your report using the formal PPDAC structure it is recommended you introduce your topic with some personal background reading . For example "I recently went on a fishing boat and saw sharks in the water. I am interested in seeing if male sharks are longer in length than female sharks. OR, "I was watching a David Attenborough documentary on NZ kiwi and I wondered if the male kiwi were larger than the female kiwi...etc"
Try and make the report your own here because the rest of it will read pretty much the same as everyone else in the class. Stand out!
PROBLEM
I wonder if the median weights of male kiwi tend to be greater than the median weights of female kiwi back in the population. From my own observations, the males of most species tend to be larger or heavier than the female so I expect this to occur with kiwi too.
PLAN
I will take my random sample from NZGrapher. The sample size is 364 female and 336 male kiwi. NZGrapher will generate a dot plot and a box and whisker graph with 5 number summaries so I can analyze and make a conclusion about which gender of kiwi is heavier.
Try and make the report your own here because the rest of it will read pretty much the same as everyone else in the class. Stand out!
PROBLEM
I wonder if the median weights of male kiwi tend to be greater than the median weights of female kiwi back in the population. From my own observations, the males of most species tend to be larger or heavier than the female so I expect this to occur with kiwi too.
PLAN
I will take my random sample from NZGrapher. The sample size is 364 female and 336 male kiwi. NZGrapher will generate a dot plot and a box and whisker graph with 5 number summaries so I can analyze and make a conclusion about which gender of kiwi is heavier.
DATA
ANALYSIS
General observations: My initial impression of these two samples is that there is a considerable difference in the median weights between female and male kiwi from the NZGrapher sample representing the population of kiwi in New Zealand. The dot plot for female kiwi has a much wider spread than the dot plot for male kiwi. However, both female and male kiwi graphs follow a normal distribution curve (unimodal or symmetrical). There are some small gaps in the dot plots of both female and male graphs.
class notes on graph shape
Central Tendency:
The median weight for female kiwi is greater at 2.90 kg and the median weight for male kiwi is 2.25 kg, a difference of 0.65 kg. This indicates that the average female kiwi could be heavier than average male kiwi back in the population (data base sample of NZGrapher).
Spread:
The IQR (middle 50%) for female kiwi weight is 0.57 kg whereas the IQR for male kiwi weight is 0.36 kg. This indicates that there is more variation in the weights of female kiwi. Overall visually the female kiwi seem to be more spread out than the male kiwi.
Middle 50% (Interquartile range or IQR): (Merit/Excellence)
Overlap:
The middle 50% (IQR) for female kiwi weights are between 2.622 kg and 3.192 kg, whereas the middle 50% (IQR) for male kiwi weights are between 2.069 kg and 2.429 kg. There is no overlap of the middle 50% (IQR's) for female and male kiwi.
Shift:
The lower quartile for female kiwi weights (2.622 kg) is higher than the upper quartile for the male kiwi weights (2.429 kg)
The IQR (middle 50%) for female kiwi weight is 0.57 kg whereas the IQR for male kiwi weight is 0.36 kg. This indicates that there is more variation in the weights of female kiwi. Overall visually the female kiwi seem to be more spread out than the male kiwi.
Middle 50% (Interquartile range or IQR): (Merit/Excellence)
Overlap:
The middle 50% (IQR) for female kiwi weights are between 2.622 kg and 3.192 kg, whereas the middle 50% (IQR) for male kiwi weights are between 2.069 kg and 2.429 kg. There is no overlap of the middle 50% (IQR's) for female and male kiwi.
Shift:
The lower quartile for female kiwi weights (2.622 kg) is higher than the upper quartile for the male kiwi weights (2.429 kg)
Shape:
The distribution of the weights of female and male kiwi are both relatively symmetrical with the with the LQ and UQ for female weights (2.622 kg and 3.192 kg, respectively) about 300 g from the median of 2.9 kg. Similarly, the LQ and UQ for male weights (2.069 kg and 2.429 kg respectively) about 180 g from the median of 2.246 kg.
I think the distributions of weights of female and male kiwi would also be symmetrical in the population of kiwi in New Zealand.
The distribution of the weights of female and male kiwi are both relatively symmetrical with the with the LQ and UQ for female weights (2.622 kg and 3.192 kg, respectively) about 300 g from the median of 2.9 kg. Similarly, the LQ and UQ for male weights (2.069 kg and 2.429 kg respectively) about 180 g from the median of 2.246 kg.
I think the distributions of weights of female and male kiwi would also be symmetrical in the population of kiwi in New Zealand.
Special features: (Excellence only)
Looking at the graphs I can see that the female kiwi have one sample that weighs more than all other kiwi. Referring to NZGrapher this particular bird is a great spotted kiwi weighing 4.143 kg. This bird could be an older one or carrying an egg which can account for up to 20% of a kiwi's body weight. https://www.kiwisforkiwi.org/about-kiwi/kiwi-facts-characteristics/enormous-egg/It could also have been kept in captivity and 'fattened up' before its release. This species of kiwi is generally larger than the other species like the North Island brown kiwi and the Southern Tokoeka. Age is another factor that might account for smaller birds of each gender as younger birds would be lighter than older birds, heavier.
Looking at the graphs I can see that the female kiwi have one sample that weighs more than all other kiwi. Referring to NZGrapher this particular bird is a great spotted kiwi weighing 4.143 kg. This bird could be an older one or carrying an egg which can account for up to 20% of a kiwi's body weight. https://www.kiwisforkiwi.org/about-kiwi/kiwi-facts-characteristics/enormous-egg/It could also have been kept in captivity and 'fattened up' before its release. This species of kiwi is generally larger than the other species like the North Island brown kiwi and the Southern Tokoeka. Age is another factor that might account for smaller birds of each gender as younger birds would be lighter than older birds, heavier.
Conclusion:
Based on looking at my sample I am reasonably confident that back in the population of all kiwi in New Zealand that the median weight of female kiwi tends to be greater than the median weight of male kiwi. The distance between the medians compared to the overall visible spread is greater than than one third. Female kiwi tend to be heavier on average than male kiwi back in the population of NZ kiwi. This surprised me as I expected the male birds to be on average heavier.
Based on looking at my sample I am reasonably confident that back in the population of all kiwi in New Zealand that the median weight of female kiwi tends to be greater than the median weight of male kiwi. The distance between the medians compared to the overall visible spread is greater than than one third. Female kiwi tend to be heavier on average than male kiwi back in the population of NZ kiwi. This surprised me as I expected the male birds to be on average heavier.
Because the sample sizes around 30 I have to use the DBM/OVS rule. The DBM is about 30 and the OVS is about 60. The ratio is 30/60 = 0.5 If the DBM/OVS is > 1/3 I can make the call that the median weights of female kiwi tend to be greater than the median weights of male kiwi.
I am reasonably confident about this call but I might get a different answer if I took another sample. Another sample would have different data points and would produce different graphs that could lead me to a different answer, although I think this is very unlikely. It is unlikely because of the big shift between the medians in my samples and the high value of the DBM/OVS ratio