Transcript Quick Guide to Stats

Very Short Guide to Stats
for SGR
Basics of aggregate and statistical
data
Inferential v. Descriptive
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Descriptive statistics “describe” the data of a
sample or population. They are usually
aggregate data
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Average (Mean) GPA
Standard Deviation of SAT score
Inferential statistics “infer” (i.e. conclude)
relationships between a sample AND a
population, or “infer” past, present or future
results of a sample/population based on its data.
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Regression/correlation analysis of GPA and SAT
(relationship between SAT and GPA, and SAT can be
used to predict GPA)
Population v. Sample
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In inferential statistics, you would refer to the number of
participants in your survey as N. If it is a sample or part
of a whole, it is n (lowercase), and if it is a total
population, it is N (uppercase).
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In descriptive studies and descriptive statistics, it is
common to refer to participants as N, subgroups of those
participants as n
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Population: N = 4,432
Sample: n = 100
Of the total students surveyed (N = 100), only 10% (n = 10) were
male.
For the SGR, you would refer to then the participants as
N since this is a descriptive study.
Descriptive Stats 101
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Central Tendency measures common “middles”
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Mean is the arithmetic average of items or values
Mode is the most occurring item or value
Median is the item or value of which 50% are greater and 50% are less.
Sometimes GPA or time can be used as a measure, but another
measure is one of attitudes and beliefs using a Likert-type scale.
Standard Deviation is a measure of the spread of items or values in
a series. Understanding the variation can help you see how close a
particular item or value is to other numbers.
Distribution (Histogram) is a visual representation of the number of a
particular result in an array of numbers.
In this series (number of hours I played WoW over break):
8, 0, 0, 3, 2, 10, 0
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Mean = 3.29, Mode = 0, Median = 2, SD = 4.11
In this series (number of hours I worked this week):
8, 8, 8, 8, 6, 6, 5
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Mean = 7, Mode = 8, Median = 8, SD = 1.29
Using Excel to do your stats
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Mean { =average(range) }
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You can compute mode { =mode(range) } or median {=median(range) },
but they might not be as useful in this project.
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Standard Deviation { =stdev(range) }
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You can also count the number of instances of a value including
instances of text: { =countif(range,”value”) }
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The following example would count every instance of “male” in the
range:
=countif(A2:A7,”male”)
You can create frequency distribution histograms by using Tools ->
Data Analysis, then Historgram. Histograms count the number of
instances of a result in a given array.
You can also find these commands by using Insert -> Function. There are also far
more complex inferential statistics available in Excel
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You can do a complete Descriptive Stats Summary by selecting Tools > Data Analysis (If you
don’t see a Data Analysis, then (Excel 2003) Tools > Add-ins > Analysis ToolPak; (Excel 2007)
Excel Options > Add-ins > Manage Add-ins > Analysis ToolPak
Writing Stats in APA
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Standard Deviation = SD
Mean = M
Descriptive statistics are often written in parentheses
after an item that the statistic refers to, and symbols and
numbers should be separated by a space
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In a survey of DU students, participants (N = 100) responded
that money was more important (M = 4.2, SD = .9) than
experience (M = 3.5, SD = .76) in selecting a summer job.
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In a survey of computer game addicts, females (n = 15) were
more likely to be depressed during withdrawal (M = 5.2, SD =
.45) than males were (n = 78, M = 3.2, SD = .98)
If unsure about how to write a statistic in your SGR, you can consult the
APA Manual (in the library), ask me, or visit
http://www.docstyles.com/apa17.htm
Charts and Graphs
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Pie graphs – good for showing distributions of a total
population (you will have to compute aggregates first)
Line graphs – good for showing time-based, linear
progression
Column/Bar graphs – good for showing distribution of
individual responses (you will have to create aggregates
first)
Y-Axis (vertical) for variables, X-Axis (horizontal) for
participants.
Exercise
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Perform countif function on gender and major (you will
have to create an area for your results that lists the
gender/major options). This is just practice doing these
two functions and you don’t have to relate them to the
next steps.
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Pick two or more variables to compare and write a
paragraph in APA style using appropriate symbols (M,
SD, N, n ) about the data.
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Create a graph of some variable or detail of the data,
labeling the legend and series items.