Codebook.md

Codebook for "tidyset.txt"

Introduction and background

In reviewing the features_info document, we find a few important facts that help to understand the nature of the measurements within the original data set. These differences are the basis of the construction of variable names in the original data set, and are modified in this codebook. Specifically:

• the phones have built-in accelerometer and gyroscopes whihc capture data along 3 axes (X, Y, and Z).
• the raw measurements were sampled at a constant rate of 50 Hz, meaning that they are recorded at regular time interval (variables beginning with t in the raw data)
• the raw signals were analyzed (various filters) to remove noise and distinguishe between Body acceleration and gravity accerlation (Dody or Gravity in the column name)
• Further computations from the raw data genearated the angular velocity and "Jerk" (defined as the first derivative of acceleration.
• some of the transformed variables were further analyzed to create a set of frequency domain signals. These variables begin with the letter f in the list below.

Naming conventions in this file

Except for columns 1, 2 and 69 every value in the table is the mean of multiple measures, as specified in the project assignment.

• Most variables are time domain; those starting with f are frequency domain.
• Any variable containing a capital M refers to a mean; S refer to a standard deviation
• All acceleration measures refer either to Body or Gravity
• The letters Acc in a variable indicate that the source was the phone accelerometer
• The letters Gyro indicate that the sourece was the gyroscope
• Mag indicates a computed magnitude (non-axial)
• Jerk indicates a computed first derivative of accleration

Data Dictionary

Many of the following variables are axial (X-, Y-, Z-). In those instances, there is a definition for the X direction only. Magnitude variables (ending in "Mag") are non-directional

Column	Variable Name	Comments
1	SubjID	Subject ID number
2	ActID	Activity ID number (see last column for descriptor)
3	BodyAccM...X	Body acceleration Mean along X axis (next 2 refer to Y and Z)
4	BodyAccM...Y
5	BodyAccM...Z
6	GravAccM...X	Gravity acceleration Mean along X axis
7	GravAccM...Y
8	GravAccM...Z
9	BodyAccJerkM...X	Body acceleration Jerk Mean along X axis
10	BodyAccJerkM...Y
11	BodyAccJerkM...Z
12	BodyGyroM...X	Body Gyro Mean along X-axis
13	BodyGyroM...Y
14	BodyGyroM...Z
15	BodyGyroJerkM...X	Body Gyro Jerk Mean along X-axis
16	BodyGyroJerkM...Y
17	BodyGyroJerkM...Z
18	BodyAccMagM..	Body Acc Magnitude Mean
19	GravAccMagM..	Gravity Acc Magnitude Mean
20	BodyAccJerkMagM..	Body Acc Jerk Magnitude Mean
21	BodyGyroMagM..	Body Gyro Magnitude Mean
22	BodyGyroJerkMagM..	Body Gyro Jerk Magnitude Mean
23	fBodyAccM...X	Body acceleration Mean along X axis (frequency domain
24	fBodyAccM...Y
25	fBodyAccM...Z
26	fBodyAccJerkM...X	Body acceleration Jerk Mean along X axis (freq)
27	fBodyAccJerkM...Y
28	fBodyAccJerkM...Z
29	fBodyGyroM...X	Body Gyro Mean along X axis (freq)
30	fBodyGyroM...Y
31	fBodyGyroM...Z
32	fBodyAccMagM..	Body Acc Magnitude Mean(freq)
33	fBodyBodyAccJerkMagM..	Body Acc Jerk Magnitude Mean(freq)
34	fBodyBodyGyroMagM..	{not clear what the double Body indicates}
35	fBodyBodyGyroJerkMagM..	{not clear what the double Body indicates}
36	BodyAccS...X	Same as columns 3:35, except that remaining columns are for std deviations
37	BodyAccS...Y
38	BodyAccS...Z
39	GravAccS...X
40	GravAccS...Y
41	GravAccS...Z
42	BodyAccJerkS...X
43	BodyAccJerkS...Y
44	BodyAccJerkS...Z
45	BodyGyroS...X
46	BodyGyroS...Y
47	BodyGyroS...Z
48	BodyGyroJerkS...X
49	BodyGyroJerkS...Y
50	BodyGyroJerkS...Z
51	BodyAccMagS..
52	GravAccMagS..
53	BodyAccJerkMagS..
54	BodyGyroMagS..
55	BodyGyroJerkMagS..
56	fBodyAccS...X
57	fBodyAccS...Y
58	fBodyAccS...Z
59	fBodyAccJerkS...X
60	fBodyAccJerkS...Y
61	fBodyAccJerkS...Z
62	fBodyGyroS...X
63	fBodyGyroS...Y
64	fBodyGyroS...Z
65	fBodyAccMagS..
66	fBodyBodyAccJerkMagS..
67	fBodyBodyGyroMagS..
68	fBodyBodyGyroJerkMagS..
69	Activity	Descriptive name of the activity (e.g. Walking, Sitting)