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2.5.2 Collecting Data
Dad meets with Tere to discuss the data collection effort. Dad convinces Tere that
she should keep a detailed log of data regarding second semester expenditures, either
paid for with a credit card or cash. Although Tere is reluctant, Dad convinces her
that he will be fair in his analysis. They agree on a list of the most important issues
and concerns he wants to address regarding expenditures:
1. What types of purchases are being made?
2. Are there interesting patterns occurring during the week, month, and semester?
3. How are the payments of expenditures divided among the credit card and cash?
4. Can some of the expenditures be identiﬁed as unnecessary?
To answer these questions, Dad assumes that each time an expenditure occurs,
with either cash or credit card, an observation is generated. Next, he selects 6 data
ﬁelds to describe each observation: (1) the number of the week (1–15) for the
15 week semester in which the expenditure occurs, (2) the date, (3) the weekday
M, etc.) corresponding to the date, (4) the amount of
the expenditure in dollars, (5) whether cash (C) or credit card (R) was used for
payment, and ﬁnally, (6) one of three categories of expenditure types-food (F), per-
sonal (P), and school (S). Note that these data elements represent a wide variety
of data types, from ratio data related to Amount, to categorical data representing
food/personal/school, to ordinal data for the date. In Table 2.4 we see that the ﬁrst
observation in the ﬁrst week was made by credit card on Sunday, January 6th for
food in the amount $111.46. Thus, we have collected our data and now we can begin
to consider summarization.
2.5.3 Summarizing Data
Let’s begin the process of data analysis with some basic exploration; what is often
referred to as a ﬁshing expedition . It is called a ﬁshing expedition, because we sim-
ply want to perform a cursory examination of the expenditures with no particular
analytical direction in mind, other than becoming acquainted with the data. This
initial process should then lead to more explicit directions for the analysis; that is,
we will go where the ﬁshing expedition leads us. Summarization of the data will
be important to us at this stage. Exhibit 2.13 displays the data in a loose chrono-
logical order, but it does not provide a great deal of information for a number of
reasons. First, each successive observation does not correspond to a strict chrono-
logical order. For example, the ﬁrst seven observations in Exhibit 2.13 represent
Sunday, Monday, Tuesday, Thursday, Sunday, Monday, and Monday expenditures,
respectively. Thus, there are situations where several expenditures occur on the same
day and there are days where no expenditures occur. If Dad’s second question about
patterns of expenditures is to be answered, we will have to modify the data to include
all days of the week and impose strict chronological order; thus, our chart should