Understanding Data – Class 12 Computer Science notes, important questions and MCQs

Chapter overview

Data is a collection of facts, figures and observations that can be processed to obtain information. Data may be structured or unstructured and is collected, stored, processed and analysed to support decisions. Statistical techniques such as measures of central tendency (mean, median, mode) and measures of variability (range, standard deviation) are used to summarise and understand data.

Data collection, storage and processing

• Structured data is organised in a fixed format such as tables; unstructured data has no predefined format, such as images, videos and text messages.
• Data is collected through surveys, sensors, transactions and online forms; it is stored on hard disks, SSDs, servers and the cloud; data processing includes input, processing (such as sorting, calculating and summarising) and output.
• Data must be checked for accuracy and completeness; files such as CSV are common for storing tabular data.

Statistical techniques

• Mean is the sum of values divided by the number of values; median is the middle value of sorted data (average of the two middle values when n is even); mode is the most frequent value.
• Range is the difference between the maximum and minimum values; standard deviation measures how much values spread from the mean, as the square root of the average of squared deviations.
• For the data 2, 4, 4, 4, 5, 5, 7, 9: mean = 5, median = 4.5, mode = 4, range = 7 and population standard deviation = 2. Python's statistics module provides mean(), median(), mode() and pstdev().

Key terms

Data

raw facts and figures that can be processed

Structured data

data organised in a fixed format such as rows and columns

Mean

the sum of values divided by their count

Median

the middle value of sorted data

Standard deviation

a measure of spread of values around the mean

Important questions with answers

Quick revision

• Structured and unstructured data.
• Data collection, storage and processing.
• Mean, median, mode.
• Range and standard deviation.

Exam tips

• Sort the data before finding the median.
• Practise mean, median, mode and range on the same data set.

Practice MCQs

1. The most frequently occurring value in a data set is the

   1. mean
   2. range
   3. median
   4. mode
   Show answer

   Answer: (d) mode. It may be more than one.

2. Images and videos are examples of

   1. structured data
   2. metadata only
   3. unstructured data
   4. numeric data
   Show answer

   Answer: (c) unstructured data. They have no fixed tabular format.

3. The difference between the largest and smallest values is the

   1. mean
   2. median
   3. mode
   4. range
   Show answer

   Answer: (d) range. It is a simple measure of spread.

4. The mean of 10, 20, 30, 40 is

   1. 20
   2. 25
   3. 30
   4. 100
   Show answer

   Answer: (b) 25. 100 ÷ 4 = 25.

5. The median of 7, 3, 9, 5, 1 is

   1. 3
   2. 5
   3. 7
   4. 9
   Show answer

   Answer: (b) 5. Sorted: 1, 3, 5, 7, 9.

6. The median of 2, 4, 6, 8 is

   1. 5
   2. 4
   3. 6
   4. 4.5
   Show answer

   Answer: (a) 5. (4 + 6) ÷ 2 = 5.

7. The population standard deviation of 2, 4, 4, 4, 5, 5, 7, 9 is

   1. 1
   2. 2
   3. 4
   4. 5
   Show answer

   Answer: (b) 2. The mean is 5 and the variance is 4.

8. Which measure is least affected by one extremely large value

   1. mean
   2. range
   3. median
   4. standard deviation
   Show answer

   Answer: (c) median. It depends only on the middle position.