Análisis Descriptivo de Datos: Medidas Centrales, Dispersion y Forma, Apuntes de Biología

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UNIT 5

UNIVARIATE DESCRIPTIVE

STATISTICS

“Tècniques de recerca“

UNIT 5

PART 5.1:

CATEGORICAL VARIABLES

 Qualitative or categorical variables: measured in nominal scale.

 Operations allowed: classification of the participants according to the quality of interest – presence or absence of a specific feature.

 Categories should be exhaustive and mutually exclusive.

What are qualitative data?

Information is obtained about a small village (n = 60 ):

 Main concern people are worried about

 Cross-sectional diagnosis of depression

 Longitudinal diagnosis of depression

 Satisfaction with the life in the village

 Income

 Power in deciding the future of the village

 Voting power in relation to legal aspects

 Number of children

Example

Frequency table: Example 1

“Concerns” variable n i : absolute frequency Ni : accumulated frequency f i = n i/N : relative frequency Fi : accumulated relative frequency p i = ( n i/N) : individual proportion P i = ( n i/N) x 100 : individual percentage

• Based on the frequency tables.
• Pie chart
• Bar plot

Graphical representations: Example 1

EXAMPLE 2

ID V1 V2 V3 V4 V5 V6 V7 V8 V9 V

ID - identifier

V1 - Sex

1 - man

2 - woman

V2 - Age

V3 – Civil status

1 - single

2 - married

3 - widower

4 - separated

V4 – Number of sons

V5 – Circulatory diseases

V6 – Respiratory diseases

V7 – Mental diseases

1 - Yes

0 - No

V8 - AVDI

V9 - AVD

V10 - MEC-Lobo

Frequency tables and graphics: R-Commander output (Example 2)

Summary indices

Graphics:

Single Married Civil_Status Widower Separated

Frequency

0

2

4

6

8

10

Bar chart

Pie chart

Single

Married

Widower

Separated

Civil_Status

Civil status fi pi Pi Fa pa Pa Single 4 0,2 20 4 0,2 20 Married 4 0,2 20 8 0,4 40 Widower 11 0,55 55 19 0,95 95 separated 1 0,05 5 20 1 100 Total 20 1 100

R-Commander output: Example 2

Civil status fi pi Pi Fa pa Pa Single 4 0,2 20 4 0,2 20 Married 4 0,2 20 8 0,4 40 Widower 11 0,55 55 19 0,95 95 separated 1 0,05 5 20 1 100 Total 20 1 100

Odds for widower: 11 / 9 = 1. 22 widower per each other in the sample

 In a study on child depression, a sample of 1300 8 - 10 year-old children is followed during three years. At the beginning of the period there are 90 children diagnosed with depression. At the end of the period this tally is increased to 130.

(^90) .069 (6.9%) P I  1300 

OBSERVATION PERIOD

(^130) .10 (10%) P F  1300 

(^130 90 40) .033 (3.3%) IA (^)  1300 90 1210     

Prevalence vs. incidence: Example

UNIT 5

PART 5.2:

QUANTITATIVE VARIABLES

(ORDINAL SCALES)

Recommended readings

• Solanas, A., Salafranca, Ll., Fauquet, J. y Núñez, M. I. (2005). Estadística

descriptiva en ciencias del comportamiento. Madrid: Thomson.

 Where: p1 4/2 EST

 What: Chapters 7 + 9

• Guàrdia, J., Freixa, M., Peró, M. y Turbany, J. (2008). Análisis de datos en

psicología (2ª ed.). Madrid: DELTA Publicaciones..

 Where: p1 4/2 ANA

 What: Chapter 4

• Peró, M., Leiva, D., Guàrdia, J. y Solanas, A. (Eds.) (2012). Estadística

aplicada a las ciencias sociales mediante R y R-Commander. Madrid: Garceta.

 Where: p2 311 EST

 What: Chapter 4

Md

P 10 P 20 P 30 P 40 P 50 P 60 P 70 P 80 P 90

D 1 D 2 D 3 D 4 D 5 D 6 D 7 D 8 D 9

Q 1 Q 2 Q 3

O 1 O 2 O 3 O 4 O 5 O 6 O 7

P 25 P 75

Types of quantiles (median, deciles, quartiles, etc.)

Measures based on position

Position or location measures

Approach calculation of position measures:

INTERPOLATION TECHNIQUE Determining the value from the estimation of the position and specification of the Xi value indicating the percentile, decile or quartile of interest.