Observation

Definition

A observation is a statistical unit on which are carried out a serie of measures

A classical data set in statistics is a table where each line represents an observation and each row represent the same measure carried out on all the observations

It can be useful sometimes to consider a group of observations as a single observation, in this case the measures carried out are agregated measures on the group of observations (percentage, mean, sum, minimal value, maximal value, etc...)

Example 1
    variable 1 variable 2 variable 3 variable 4
  name gender age height weight
observation 1 Aubrey M 41 74 170
observation 2 Ron M 42 68 166
observation 3 Carl M 32 70 155
observation 4 Antonio M 39 72 167
observation 5 Deborah F 30 66 124
observation 6 Jacqueline F 33 66 115
observation 7 Helen F 26 64 121
observation 8 David M 30 71 158
observation 9 James M 53 72 175
observation 10 Michael M 32 69 143
observation 11 Ruth F 47 69 139
observation 12 Joel M 34 72 163
observation 13 Donna F 23 62 98
observation 14 Roger M 36 75 160
observation 15 Yao 23 M 70 145
observation 16 Elizabeth F 31 67 135
observation 17 Tim M 29 71 176
observation 18 Susan F 28 65 131

Example 2

Example of group observations considered as single observations

The data are per capita numbers of cigarettes smoked (sold) by 43 states and the District of Columbia in 1960 together with death rates per thouusand population from various forms of cancer.

Number of cases: 44

Variable Names:

CIG = Number of cigarettes smoked (hds per capita)

BLAD = Deaths per 100 population from bladder cancer

LUNG = Deathes per 100 population from lung cancer

KID = Deaths per 100 population from bladder cancer

LEUK = Deaths per 100 population from leukemia
 
STATE CIG BLAD LUNG KID LEUK
AL 18.20 2.90 17.05 1.59 6.15
AZ 25.82 3.52 19.80 2.75 6.61
AR 18.24 2.99 15.98 2.02 6.94
CA 28.60 4.46 22.07 2.66 7.06
CT 31.10 5.11 22.83 3.35 7.20
DE 33.60 4.78 24.55 3.36 6.45
DC 40.46 5.60 27.27 3.13 7.08
FL 28.27 4.46 23.57 2.41 6.07
ID 20.10 3.08 13.58 2.46 6.62
IL 27.91 4.75 22.80 2.95 7.27
IN 26.18 4.09 20.30 2.81 7.00
IO 22.12 4.23 16.59 2.90 7.69
KS 21.84 2.91 16.84 2.88 7.42
KY 23.44 2.86 17.71 2.13 6.41
LA 21.58 4.65 25.45 2.30 6.71
ME 28.92 4.79 20.94 3.22 6.24
MD 25.91 5.21 26.48 2.85 6.81
MA 26.92 4.69 22.04 3.03 6.89
MI 24.96 5.27 22.72 2.97 6.91
MN 22.06 3.72 14.20 3.54 8.28
MS 16.08 3.06 15.60 1.77 6.08
MO 27.56 4.04 20.98 2.55 6.82
MT 23.75 3.95 19.50 3.43 6.90
NB 23.32 3.72 16.70 2.92 7.80
NE 42.40 6.54 23.03 2.85 6.67
NJ 28.64 5.98 25.95 3.12 7.12
NM 21.16 2.90 14.59 2.52 5.95
NY 29.14 5.30 25.02 3.10 7.23
ND 19.96 2.89 12.12 3.62 6.99
OH 26.38 4.47 21.89 2.95 7.38
OK 23.44 2.93 19.45 2.45 7.46
PE 23.78 4.89 12.11 2.75 6.83
RI 29.18 4.99 23.68 2.84 6.35
SC 18.06 3.25 17.45 2.05 5.82
SD 20.94 3.64 14.11 3.11 8.15
TE 20.08 2.94 17.60 2.18 6.59
TX 22.57 3.21 20.74 2.69 7.02
UT 14.00 3.31 12.01 2.20 6.71
VT 25.89 4.63 21.22 3.17 6.56
WA 21.17 4.04 20.34 2.78 7.48
WI 21.25 5.14 20.55 2.34 6.73
WV 22.86 4.78 15.53 3.28 7.38
WY 28.04 3.20 15.92 2.66 5.78
AK 30.34 3.46 25.88 4.32 4.90
 
Data from J.F. Fraumeni, "Cigarette Smoking and Cancers of the Urinary Tract: Geographic Variations in the United States," Journal of the National Cancer Institute, 41, 1205-1211.