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Psy 315 Statistics practice problems Chapter2




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Statistics practice problems
Katherine Sainz
University of Phoenix

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Week 2 Individual Assignment
Chapter 1, Practice Problems: 12, 15, 19, 20, 21 and 22.
12. Explain and give an example for each of the following types of variables:
a) Equal-interval,
An equal-interval variable is a variable in which the numbers stand for approximately equal
amounts of what is being measured. For example, grade point average (GPA) is a roughly
equal-interval variable, since the difference between a GPA of 2.5 and 2.8 means about as
much as the difference between a GPA of 3.0 and 3.3 (each is a difference of 0.3 of a GPA).
Most psychologists also consider scales like the 0-to-10 stress ratings as roughly equal
interval. For example, temperature measured with Fahrenheit has equal intervals; that is, the
difference between temperatures of 30 and 31 degrees is 1 degree, and the difference between
100 and 101 degrees is 1 degree. No matter where on the scale that 1 degree is located, that 1
degree represents the same amount of heat.
b) Rank-order :
Psychologists use rank-order variables because they are the only information available. Also,
when people are being asked to rate something, it is sometimes easier and less subjective for
them to make rank-order ratings. A Rank Order scale gives the respondent a set of items and
asks them to put the items in some form of order. The measure of 'order' can include such as
preference importance, liking, effectiveness and so on. The order is often a simple ordinal
structure (A is higher than B). It can also be done by relative position (A scores 10 whilst B
scores 6).
C) Nominal: variable with values that are categories (that is, they are names rather than
numbers) also called categorical variable. Where the subject falls into a category, but one
category is not considered to be higher or lower than another
For example, if you buy a $900 bond and are paid $1,000 for it a year later, your rate of
return is 11.1%. This is the nominal rate of return; it is unadjusted and reflects the return on
your bond. However, to get a more accurate picture of the actual return, the rate needs to be
adjusted for inflation because the purchasing power of your money has likely changed over
the one-year period. Therefore, if inflation for that year is 5%, the real rate of return is only
6.1% (11.1%-5%).
D) Ratio scale
An equal-interval variable is measured on a ratio scale if it has an absolute zero point,
meaning that the value of zero on the variable indicates a complete absence of the variable.

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A rational zero is a location on an interval scale deliberately chosen for reasons other than the
current data. The distinctive feature of a ratio scale is that it has an origin defined by a
dominating theory. Maps usually contain ratios telling you how many inches on the map
relate to how many miles of the actual area covered by the map. For example, "1 inch = 1.5
E) Continuous: variable for which, in theory, there are an infinite number of values between
any two values. Data that consist of a large number of values, with no particular category
label attached to any particular data value. For example: A person's weight can be 150.3 lbs,
150.446 pounds and so on. Discrete variables, on the other hand can only assume a finite
number of values. For example, number of people in a movie theatre. There are no clear cut
or sharp breaks between possible values.
Following are the speeds of 40 cars clocked by radar on a particular road in a
35-mph zone on a particular afternoon:
30, 36, 42, 36, 30, 52, 36, 34, 36, 33, 30, 32, 35, 32, 37, 34, 36, 31, 35, 20,
24, 46, 23, 31, 32, 45, 34, 37, 28, 40, 34, 38, 40, 52, 31, 33, 15, 27, 36, 40
A) Make a frequency table
15 1
20 1
23 1
24 1
27 1
28 1
30 3

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