Data Processing and Descriptive Analysis
I. Today’s class
--review procedures for data processing
--illustrate some of these issues, particularly missing data, with NELS 8th grade survey
--review of Teleform
II. What’s involved in data processing?
--coding data
--entering data
--managing data
--cleaning data
--recoding data
--handling missing data
--creating scales and indexes
--generating descriptive statistics
III. Coding Data
--coding scheme is a set of rules for creating usable data from questionnaire responses
--should be done as early as possible in design stage
--should reflect how data will be used in analysis (e.g., creation of dummy variables for multivariate analysis)
--should provide unique codes for various types of valid and invalid answers as well as non-responses
e.g. NELS88
BYP40 NO. OF TIMES 8TH GRADER CHANGED SCHOOLS
Frequency Percent Valid Percent Cumulative Percent
Valid 0 NONE 9584 39.0 43.3 43.3
1 ONCE 5093 20.7 23.0 66.3
2 TWICE 25
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DATA STRUCTURES
ORGANISATION OF DATA
Characters, facts, records, files and databases form an organisation of data. The basic building
block of data is a character. The character consists of upper and lower-case letter, numeric digits
or symbols. Upper and lower-case letters are Aa, Bb, Cc,… Zz. Numeric digits are 0, 1, 2,..,9.
Symbols involve commas (,) quotation mark (?) plus (+) division (/) and so on. Upper and lowercase
letters are called alphabetic character. Numeric digits are called numeric character. Symbol
is called special characters. A combination of the three types is called alphanumeric characters
(#2B, N2.50K). A computer can accept both alphanumeric and numeric and store them in
memory.
Characters are put together to form a fact. A fact is also called a field. A fact or field is a number,
an item, word, name or a combination of characters. Facts are put together to form a record. A
record is a related items of data in a file. An employee record in a
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INFORMATION OR DATA REPRESENTATION
There are three ways of representing information or data in computer system. These are as
follows:
Number System
Character codes
Logic gates and Truth Table
4.1 NUMBER SYSTEMS
Number Systems include Binary number, Octal number, Hexadecimal number, Binary Fraction,
Arithmetic operation, Negative numbers, Fixed-point and Floating Point representation and
Errors.
Binary Number – This method is used to represent information with two-state circuits. These
two states are 0 or 1. These two states are used in computer because they are quick, reliable and
take up only small amounts of space and energy. They are called binary digits or bits.
Conversion from Binary to Decimal
e.g. 0110 = 0x23 + 1x22 + 1 x21 + 0 + 20
= 0 + 4 + 2 + 0
01102 = 610
Conversion from Decimal to Binary
2 6
2 3 remainder 0
2 1 remainder 1
0 remainder
610 = 01102
OCTAL NUMBER – Octal numbers are in base 8
Conversion from Decimal to Octal
4910 to base 8
8 49
8
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NETWORKS
Definitions: An Interconnected collection of autonomous processors. A Network is a group of
two or more computers connected to each other by a cable, over telephone lines or through
wireless communication. When you are connected to a network, you can share resources on your
computer such as documents, programs, printers, modems and use other resources from other
computer. The key idea of a Network is that users need equal access to resources such as data,
but they do not necessarily have to have equal computing power.
LANs, WANs and ‘Client Server” concepts are perhaps the most important trend in modern
computing.
There are two types of Networks
LOCAL AREA NETWORK (LAN)
WIDE AREA NETWORK (WAN)
LOCAL AREA NETWORK (LAN)
Definition: A network of computers located in a single building or an a single site.
A LAN may also include a Bridge which is a connection to another similar LAN and a Gateway
which is a connection to a different types of network outside
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INTRODUCTION TO PROGRAMMING & FLOWCHARTS
PRINCIPLE OF GOOD PROGRAMING
a. The program requirements must be specified in full and in writing. These specifications will
be prepared by a systems analyst. A programmer has the task of converting these
specifications into a written program.
b. In developing a program, a programmer should keep working papers. He can refer back to
these papers later to check what he has done in case:
(i) there is an error in the program for correction;
(ii) the user of the program asks for a change in the program – e.g. for an extra bit of
processing on input data, perhaps to produce an additional report.
c. The working papers might include a decision table or flowchart (or both).
d. When writing a program, the programmer should try to keep it as short as possible, since this
will make more efficient use of storage capacity in the CPU. The program should therefore
be logically well- structured
e. Program should be tested when they have
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