Presented by:

Common Errors

Because we have to

Not using as intended

Using the quickest test

Poor Documentation during test

No rapport

Not following rules

Scoring errorsPoor interpretation

Raw Score• First Score

• Number Correct

Presented by: Brent Daigle, Ph.D. (ABD)

Norm Referenced Test

Compares with national average

Presented by: Brent Daigle, Ph.D. (ABD)

Scales of MeasurementNominal

Number used for category : no value

Presented by: Brent Daigle, Ph.D. (ABD)

Scales of Measurement

Ordinal

No True Zero.

Categories / Rank

Presented by: Brent Daigle, Ph.D. (ABD)

Scales of Measurement

Interval

No True Zero.

Equal Distance between each point

Presented by: Brent Daigle, Ph.D. (ABD)

Scales of Measurement

Ratio

True Zero

Equal Distance between each point

Frequency Distribution

Normal Distribution

Measures of Central tendency : How # cluster around the mean

Normal Distribution: Symmetrical , single # for

Mean/Med/Mode

Presented by: Brent Daigle, Ph.D. (ABD)

Median

1) Arrange data in order

Middle value in distribution

2) Find the middle valuePresented by: Brent Daigle, Ph.D. (ABD)

Calculating the Median(High Temperatures)

5.422

4342median

High

Date Temperature

7-Jan 32

8-Jan 32

6-Jan 35

10-Jan 41

5-Jan 42 <===Middle values

4-Jan 43 <===Middle values

9-Jan 46

11-Jan 52

2-Jan 59

3-Jan 60

Presented by: Brent Daigle, Ph.D. (ABD)

Mean

Add up, divide by number of values

n

XX

The averagePresented by: Brent Daigle, Ph.D. (ABD)

Mode

Most frequent valueDoes not take into account exact scores

Not useful with several = values

Length of Right Foot

87654321

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If we were to connect the top of each bar, we would create a frequency polygon.

Notice how there are more people (n=6) with a 10 inch right foot than any other length. Notice also how as the length becomes larger or smaller, there are fewer and fewer people with that measurement. This is a characteristics of many variables that we measure. There is a tendency to have most measurements in the middle, and fewer as we approach the high and low extremes.

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Length of Right Foot

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You will notice that if we smooth the lines, our data almost creates a bell shaped curve.

Presented by: Brent Daigle, Ph.D. (ABD)

87654321

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Length of Right Foot

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You will notice that if we smooth the lines, our data almost creates a bell shaped curve.

This bell shaped curve is known as the “Bell Curve” or the “Normal Curve.”

Presented by: Brent Daigle, Ph.D. (ABD)

Whenever you see a normal curve, you should imagine the bar graph within it.

12 13 14 15 16 17 18 19 20 21 22

Points on a Quiz

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Presented by: Brent Daigle, Ph.D. (ABD)

The mean, mode, and median

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Points on a Quiz

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987654321

12+13+13+14+14+14+14+15+15+15+15+15+15+16+16+16+16+16+16+16+16+ 17+17+17+17+17+17+17+17+17+18+18+18+18+18+18+18+18+19+19+19+19+ 19+ 19+20+20+20+20+ 21+21+22 = 867

867 / 51 = 17

12

13 13

14 14 14 14

15 15 15 15 15 15

16 16 16 16 16 16 16 16

17 17 17 17 17 17 17 17 17

18 18 18 18 18 18 18 18

19 19 19 19 19 19

20 20 20 20

21 21

22

12, 13, 13, 14, 14, 14, 14, 15, 15, 15, 15, 15, 15, 16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 17, 17, 17, 17, 17, 18, 18, 18, 18, 18, 18, 18, 18, 19, 19, 19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 22

will all fall on the same value in a normal distribution.

Now lets look at quiz scores for 51 students.

Presented by: Brent Daigle, Ph.D. (ABD)

Normal distributions (bell shaped) are a family of distributions that have the same general shape. They are symmetric (the left side is an exact mirror of the right side) with scores more concentrated in the middle than in the tails. Examples of normal distributions are shown to the right. Notice that they differ in how spread out they are. The area under each curve is the same.

Presented by: Brent Daigle, Ph.D. (ABD)

If your data fits a normal distribution, approximately 68% of your subjects will fall within one standard deviation of the mean.

Approximately 95% of your subjects will fall within two standard deviations of the mean.

Over 99% of your subjects will fall within three standard deviations of the mean.

Presented by: Brent Daigle, Ph.D. (ABD)

The mean and standard deviation are useful ways to describe a set of scores. If the scores are grouped closely together, they will have a smaller standard deviation than if they are spread farther apart.

Small Standard Deviation Large Standard Deviation

Click the mouse to view a variety of pairs of normal distributions below.

Different MeansDifferent Standard Deviations

Different Means Same Standard Deviations

Same Means Different Standard Deviations

Presented by: Brent Daigle, Ph.D. (ABD)

Presented by: Brent Daigle, Ph.D. (ABD)