# Data Collection

• Qualitative
• Quantitative

## Sources of Data

Primary: Obtained directly (not collected from someone else)

• Secondary: Using pre-collected data from someone else/some organization
• Example
• A researcher buys data from BMD to build a model of rainfall behavior
• A researcher runs an experiment to measure speed of light using a novel technique.
• A researcher makes use of the data generated by the one in example 2

## Method of Data Collection

• Direct personal Inquiry
• Indirect oral inquiry
• Mail
• Telephone etc.
• Each method has its own advantages and disadvantages;

## Sources of Secondary Data

• Published: Journal, Newspaper etc.
• Unpublished: BBS, WHO, IMF, FAO, ICDDR,B

## DIsadvantages of Secondary Data

• Purpose might be different
• Suitability
• Reliability
• Unit

# Organizing Data

## Data Classification

• Geographical
• Chronological
• Quantitative
• Qualitative

## Example

Geographical

GDP(m) 120 500

Chronological (Time series data)

Year 2015 2016
GDP(m) 120 500

Quantitative Classification

Income level 40,000-50,000 50,000-1,00,000
Frequency 120 34

## Frequency Distribution

No. of classes

• Sturges Method: $$k = 1 + 3.322 \space logN$$; where N = no. of observations
• Class Interval width = $${Range} \over {\text{Numbe rof classes}}$$

# Graphs

## Histogram

• Inclusive vs exclusive
What does it tell us

## Histogram (contd.)

Can these intervals be readily used?

(5-10); (10-15); (15-20)

(5-9); (10-14); (15-20)

If not, what should we do?

## Stem and Leaf

• key in stem and leaf plot
• How to interpret stem and leaf plot
data <- c(16, 26, 12, 10, 27, 30, 14,  1, 25, 20)
stem(data)
##
##   The decimal point is 1 digit(s) to the right of the |
##
##   0 | 1
##   1 | 0246
##   2 | 0567
##   3 | 0

## How to interpret cf and rf

Class Frequency Cumulative

Frequency (cf)
Relative

Frequency (rf)
Cumulative

Relative

Frequency (crf)
30-35 4 4 0.09 0.09
35-40 10 14 0.23 0.32
40-45 20 34 0.45 0.77
45-50 8 42 0.18 0.95
50-55 2 44 0.04 1
n=44 n=44

## Bar vs Pie

• When to use which?
• How to calculate angles?
• Can we draw on 180 degrees?

## Choose Diagram

year Sales (\$)
1996 76
1997 58
1998 95
1999 85

Category Cost(Tk.)
House rent 10,000
Utility Bill 3,000
Telecom 2000

## Frequency Polygon vs Frequency Curve

• Curve: Smoothed corners