Very Short Guide to Stats Very Short Guide to Stats for SGRfor SGR

Basics of aggregate and statistical Basics of aggregate and statistical datadata

Inferential v. DescriptiveInferential v. Descriptive Descriptive statistics “describe” the data of a Descriptive statistics “describe” the data of a

sample or population. They are usually sample or population. They are usually aggregate dataaggregate data Average (Mean) GPAAverage (Mean) GPA Standard Deviation of SAT scoreStandard Deviation of SAT score

Inferential statistics “infer” (i.e. conclude) Inferential statistics “infer” (i.e. conclude) relationships between a sample AND a relationships between a sample AND a population, or “infer” past, present or future population, or “infer” past, present or future results of a sample/population based on its data.results of a sample/population based on its data. Regression/correlation analysis of GPA and SAT Regression/correlation analysis of GPA and SAT

(relationship between SAT and GPA, and SAT can be (relationship between SAT and GPA, and SAT can be used to predict GPA)used to predict GPA)

Population v. SamplePopulation v. Sample In inferential statistics, you would refer to the number of In inferential statistics, you would refer to the number of

participants in your survey as N. If it is a sample or part participants in your survey as N. If it is a sample or part of a whole, it is of a whole, it is nn (lowercase), and if it is a total (lowercase), and if it is a total population, it is population, it is NN (uppercase). (uppercase). Population: Population: NN = 4,432 = 4,432 Sample: Sample: nn = 100 = 100

In descriptive studies and descriptive statistics, it is In descriptive studies and descriptive statistics, it is common to refer to participants as common to refer to participants as NN, subgroups of those , subgroups of those participants as participants as nn Of the total students surveyed (Of the total students surveyed (N N = 100), only 10% (= 100), only 10% (n n = 10) were = 10) were

male.male. For the SGR, you would refer to then the participants as For the SGR, you would refer to then the participants as

NN since this is a descriptive study. since this is a descriptive study.

Descriptive Stats 101Descriptive Stats 101 Central Tendency measures common “middles”Central Tendency measures common “middles”

Mean is the arithmetic average of items or values Mean is the arithmetic average of items or values Mode is the most occurring item or valueMode is the most occurring item or value Median is the item or value of which 50% are greater and 50% are less.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 Sometimes GPA or time can be used as a measure, but another measure is one of attitudes and beliefs using a Likert-type scale.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 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 series. Understanding the variation can help you see how close a particular item or value is to other numbers.particular item or value is to other numbers.

Distribution (Histogram) is a visual representation of the number of a Distribution (Histogram) is a visual representation of the number of a particular result in an array of numbers.particular result in an array of numbers.

In this series (number of hours I played WoW over break):In this series (number of hours I played WoW over break):8, 0, 0, 3, 2, 10, 08, 0, 0, 3, 2, 10, 0 Mean = 3.29, Mode = 0, Median = 2, Mean = 3.29, Mode = 0, Median = 2, SDSD = 4.11 = 4.11

In this series (number of hours I worked this week):In this series (number of hours I worked this week):8, 8, 8, 8, 6, 6, 58, 8, 8, 8, 6, 6, 5 Mean = 7, Mode = 8, Median = 8, Mean = 7, Mode = 8, Median = 8, SDSD = 1.29 = 1.29

Using Excel to do your statsUsing Excel to do your stats Mean { =average(range) }Mean { =average(range) }

You can compute mode { =mode(range) } or median {=median(range) }, but You can compute mode { =mode(range) } or median {=median(range) }, but they might not be as useful in this project.they might not be as useful in this project.

Standard Deviation { =stdev(range) }Standard Deviation { =stdev(range) }

You can also count the number of instances of a value including You can also count the number of instances of a value including instances of text: { =countif(range,”value”) }instances of text: { =countif(range,”value”) } The following example would count every instance of “male” in the range:The following example would count every instance of “male” in the range: =countif(A2:A7,”male”) =countif(A2:A7,”male”)

You can create frequency distribution histograms by using Tools -> Data You can create frequency distribution histograms by using Tools -> Data Analysis, then Historgram. Histograms count the number of instances of Analysis, then Historgram. Histograms count the number of instances of a result in a given array.a result in a given array.

You can also find these commands by using Insert -> Function. There are also far more You can also find these commands by using Insert -> Function. There are also far more complex inferential statistics available in Excelcomplex inferential statistics available in Excel

You can do a complete Descriptive Stats Summary by selecting Tools > Data Analysis (If you don’t see a 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-Data Analysis, then (Excel 2003) Tools > Add-ins > Analysis ToolPak; (Excel 2007) Excel Options > Add-ins > Manage Add-ins > Analysis ToolPak ins > Manage Add-ins > Analysis ToolPak

Writing Stats in APAWriting Stats in APA Standard Deviation = Standard Deviation = SDSD Mean = Mean = MM Descriptive statistics are often written in parentheses after an Descriptive statistics are often written in parentheses after an

item that the statistic refers to, and symbols and numbers item that the statistic refers to, and symbols and numbers should be separated by a space should be separated by a space

In a survey of DU students, participants (In a survey of DU students, participants (NN = 100) responded that = 100) responded that money was more important (money was more important (MM = 4.2, = 4.2, SDSD = .9) than experience ( = .9) than experience (MM = = 3.5, 3.5, SDSD = .76) in selecting a summer job. = .76) in selecting a summer job.

In a survey of computer game addicts, females (In a survey of computer game addicts, females (nn = 15) were more = 15) were more likely to be depressed during withdrawal (likely to be depressed during withdrawal (MM = 5.2, = 5.2, SDSD = .45) than = .45) than males were (males were (nn = 78, = 78, MM = 3.2, = 3.2, SDSD = .98) = .98)

If unsure about how to write a statistic in your SGR, you can consult the APA 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.htmManual (in the library), ask me, or visit http://www.docstyles.com/apa17.htm

Charts and GraphsCharts and Graphs

Pie graphs – good for showing distributions of a total Pie graphs – good for showing distributions of a total population (you will have to compute aggregates first)population (you will have to compute aggregates first)

Line graphs – good for showing time-based, linear Line graphs – good for showing time-based, linear progressionprogression

Column/Bar graphs – good for showing distribution of Column/Bar graphs – good for showing distribution of individual responses (you will have to create aggregates individual responses (you will have to create aggregates first)first)

Y-Axis (vertical) for variables, X-Axis (horizontal) for Y-Axis (vertical) for variables, X-Axis (horizontal) for participants.participants.

ExerciseExercise Perform countif function on gender and major (you will Perform countif function on gender and major (you will

have to create an area for your results that lists the have to create an area for your results that lists the gender/major options). This is just practice doing these gender/major options). This is just practice doing these two functions and you don’t have to relate them to the two functions and you don’t have to relate them to the next steps.next steps.

Pick two or more variables to compare and write a Pick two or more variables to compare and write a paragraph in APA style using appropriate symbols (paragraph in APA style using appropriate symbols (M, M, SD, N, nSD, N, n ) about the data. ) about the data.

Create a graph of some variable or detail of the data, Create a graph of some variable or detail of the data, labeling the legend and series items.labeling the legend and series items.