Descriptive statistics

Question

We are given a table for the city of Detroit, Michigan USA for the period of 1961 to 1973 with the following information: a column with the number of full-time police per 100,000 citizens and a column with the number of homicides per 100,000 citizens.

Year	Police	Homicides
1961	260.35	8.6
1962	269.8	8.9
1963	272.04	8.52
1964	272.96	8.89
1965	272.51	13.07
1966	261.34	14.57
1967	268.89	21.36
1968	295.99	28.03
1969	319.87	31.49
1970	341.43	37.39
1971	356.59	46.26
1972	376.69	47.24
1973	390.19	52.33

1. On the same x-axis representing the year, construct the time series of the number of police and the number of homicides on the same graph.
2.  Identify the variable that demonstrated the higher percentage increase relative to its initial value (police or homicides), and share your conclusions on the matter.
3. Did the increase in police officers have an impact on the murder rate? Why?

As a part of your assignment:

1. Utilize the concepts introduced in this unit to solve the problem below.
2.  The submission must include a clear copy of the graph. A handwritten graph is acceptable if each data point is visible on the graph.

Answer 1

Hello Uapanda,

I cannot post a graph here due to character limits, but what you can do is put years on the x-axis, label 1961 to 1973. Then put both police and homicides on the y-axis. Label from 0 to 400. Range between values will vary based on size of your graph paper or software capability. I would label by 20--as in 0, 20, 40.... You could also label by 10--0, 10, 20.... if you have enough room on your graph paper.

Now, the variable that displayed the higher percentage increase:

Police officers increased from 260.35 to 390.19, a difference of about 130, so this is about a 50% increase. Homicides increased from 8.6 to 52.33, an increase of about 44, but 44 is more than five times initial value of eight, so about a 500% increase. Homicide had the greater increase based on initial value.

I must leave the third part to you, as the conclusion you choose to draw should be your own. There is a clear relationship between police officers and homicides (as one increased, the other increased) but is this a true impact or do you think there is a third variable (aka confounding variable) that influenced this? No wrong answer there. That conclusion is up to you.