Q.Calculate the value of “lower quartile” from the data of marks obtained by 10 students in an examination.
30, 28, 18, 21, 23, 36, 38, 40, 32, 26
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🔒 Start your 14-day free trial to unlock the full solution →Concept understanding — Types of Averages
Types of Averages: From Everyday Intuition to Economic Meaning
You already use averages without thinking about it. When someone says "the average Indian earns ₹10,000 a month" or "the average temperature in Delhi is 30°C," you get a rough sense of the centre of things. But in Economics, the word "average" is not one single thing — it is a family of tools, each answering a different question.
Let's start with a simple example. Five students score: 40, 50, 60, 70, 80. What is the "average"? You probably added them up and divided by 5 — that gives 60. That is the arithmetic mean, the most common average. But what if one student scored 200 instead of 80? The sum becomes 420, divided by 5 gives 84 — but 84 is not "typical" of the group anymore; four out of five scored below it. So the arithmetic mean can be pulled by extreme values. That is where other averages step in.
1. Arithmetic Mean — The Balance Point
The arithmetic mean is the sum of all observations divided by the number of observations.
Xˉ=N∑X
Xˉ = arithmetic mean, ∑X = sum of all values, N = number of observations
For grouped data (where values are in class intervals), you use:
Xˉ=∑f∑fX
f = frequency of each class, X = mid-point of the class interval
Why it matters in Economics: The arithmetic mean is used to calculate per capita income (total national income divided by population), average price level, average cost, average revenue. It is the workhorse. But it has a weakness: it is sensitive to outliers. A few billionaires can make the "average income" of a country look much higher than what most people earn.
2. Median — The Middle Value
The median is the value that divides the data into two equal halves when arranged in order. Half the observations lie below it, half above.
For ungrouped data: arrange values in ascending order. If N is odd, the median is the 2N+1th value. If N is even, it is the average of the 2Nth and 2N+1th values.
For grouped data:
Median=L+f2N−cf×h
L = lower limit of the median class, N = total frequency, cf = cumulative frequency of the class before the median class, f = frequency of the median class, h = class width
Why it matters in Economics: The median is far more robust to extreme values. When you hear "the median household income in India is ₹X," that tells you what a typical household earns — not distorted by a handful of ultra-rich. The median is also used for wage data, housing prices, and any distribution that is skewed (not symmetric).
If the data is skewed (e.g., income distribution), the median is a better measure of "typical" than the mean. If the data is symmetric (e.g., heights of adult men), the mean and median are nearly equal.
3. Mode — The Most Frequent Value
The mode is the value that occurs most often in the data set. It is the only average that can be used for qualitative data (e.g., "the most common shoe size is 8").
For grouped data:
Mode=L+2f1−f0−f2f1−f0×h
L = lower limit of the modal class, f1 = frequency of the modal class, f0 = frequency of the class before the modal class, f2 = frequency of the class after the modal class, h = class width
Why it matters in Economics: The mode tells you the most common price, the most common income bracket, the most common size of a product demanded. In market research, the mode is crucial — if most customers want a ₹200 shirt, that is what you stock.
A data set can have more than one mode (bimodal, multimodal) or no mode at all (if every value occurs once). The mode is not always a reliable measure.
4. Geometric Mean — For Ratios and Growth Rates
The geometric mean is the nth root of the product of n values. It is used when dealing with percentages, ratios, or growth rates.
G=nX1×X2×⋯×Xn
For grouped data: G=antilog(∑f∑flogX)
Why it matters in Economics: The geometric mean is the correct average for growth rates. If a country's GDP grows by 10% in year 1 and 20% in year 2, the average growth rate is NOT (10+20)/2 = 15%. It is 1.10×1.20−1≈14.9%. The geometric mean is also used in index numbers (like the Consumer Price Index) and in calculating compound interest. …
Arrange the marks in order; the lower quartile (Q1) is found by interpolation at the ((N+1)/4)th position. …
Sort the data; Q1 at (N+1)/4 = 2.75th item = 21 + 0.75(23−21) = 22.5.
Marks: 30, 28, 18, 21, 23, 36, 38, 40, 32, 26 (N = 10).
Step 1 — Arrange in ascending order: 18, 21, 23, 26, 28, 30, 32, 36, 38, 40.
Step 2 — Position of the lower quartile (Q1) = size of the ((N + 1)/4)th item = (11/4)th = 2.75th item.
Step 3 — Interpolate: the 2.75th item lies between the 2nd item (21) and the 3rd item (23): …
- CBSE 2026Set MARCH1 markMCQQ.Which of the following is a measure of Central Tendency ?(a) Standard Deviation(b) Arithmetic Mean(c) Mean Deviation(d) Coefficient of variance
›Reveal solutionSolution
Among the options, only the arithmetic mean is a measure of central tendency — option (b).
In the Kerala Plus One (DHSE) Statistics for Economics course, measures of central tendency (averages) locate the centre of the data with one representative value; the common ones are the arithmetic mean, median and mode.
- Arithmetic Mean = sum of observations / number of observations — a classic measure of central tendency. …
- CBSE 2026Set ANNUAL1 markQ.Fill in the blank: One single figure is not________.
›Reveal solutionSolution
One single figure (average) is not sufficient to describe/compare data.
A single average represents a series by one central value, but it does not reveal the spread (dispersion) of the data. Two series can have the same average yet differ in variability. So one single figure is not sufficient to fully describe or compare data — a measure of disp …
- CBSE 2025Set ANNUAL1 markMCQQ.Write True or False: Mere averages are not sufficient for comparing series.(a) True(b) False
›Reveal solutionSolution
True — averages alone are insufficient; dispersion is also needed for comparison.
An average represents a series by a single central value but does not show how the values are spread around it. Two series can have the same average yet differ greatly in their variability (dispersion). Hence, to compare two series properly, we also need a measure of dispersion (range, standard deviation, etc.). So the statement that mere averages are not sufficien …
- CBSE 2024Set ANNUAL1 markQ.Fill in the blank: The idea of standard deviation was given by ________.
›Reveal solutionSolution
The idea of standard deviation was given by Karl Pearson.
Standard deviation — the most important and scientific measure of dispersion (the square root of the mean of the squared deviations from the mean) — was introduced by the English statistician **Karl Pears …
- CBSE 2024Set ANNUAL1 markQ.Standard deviation is an ideal and scientific measure.
›Reveal solutionSolution
True — standard deviation is the ideal, scientific measure of dispersion.
Standard deviation is regarded as the ideal and most scientific measure of dispersion because it is based on all the observations, is rigidly defined, is capable of further algebraic treatment, and is least affected by sampling fluctuations. For these reasons it is preferred over the r …
- CBSE 2023Set ANNUAL1 markMCQQ.Write True or False: Mere average is not sufficient to compare series.(a) True(b) False
›Reveal solutionSolution
True — an average alone is insufficient; dispersion is also needed for comparison.
An average (central value) represents the whole series by a single figure, but it does not reveal how the values are spread around it. Two series can have the same average yet differ greatly in their spread (dispersion). Therefore, to compare two series properly, we also need a measure of dispersion (range, standard deviation, etc.) along with the average. Hence the statement that a mere averag …
- CBSE 2023Set ANNUAL1 markQ.Write the answer in one word or one sentence: What is dispersion?
›Reveal solutionSolution
Dispersion = the extent of scatter (spread) of values around the average.
Dispersion refers to the degree to which the individual values of a series are scattered (spread out) around a central value (average). It measures the variability of the data — how far the values differ from the average and from one another. A small dispersion means the values are close to the average (more uniform); a large dispersion means they are widely spread. It is measured by the range, qua …
- CBSE 2022Set MARCH1 markMCQQ.Which one is a measure of Central Tendency ?(a) Median(b) Range(c) Correlation(d) Index Number
›Reveal solutionSolution
Median is a measure of central tendency; the others are not.
In the Kerala Plus One (DHSE) economics/statistics chapter on Measures of Central Tendency, an average locates the central value of a distribution. The main measures are the arithmetic mean, the median and the mode.
- Median — the middle value; a genuine measure of central tendency. …
- CBSE 2020Set MARCH1 markMCQQ.Range is the(a) a) Difference between the largest and the smallest values of a variable(b) b) Average of the largest and smallest observation.(c) c) Ratio of the largest and smallest values of a variable.(d) d) None of the above
›Reveal solutionSolution
The correct answer is (a). Range is defined as the difference between the largest (L) and the smallest (S) values in a data set, i.e. Range = L − S.
In 1st PUC Economics (Statistics), the range is the easiest measure of dispersion to calculate. It considers only the two extreme observations and ignores all the values in between. Because of this, it gives a quick idea of the spread of the data but is heavily affected by extreme values (outliers).
…
- CBSE 2020Set MARCH1 markQ.What is mean deviation ?
›Reveal solutionSolution
Mean deviation is the average of the absolute (sign-ignored) deviations of the observations from a central value such as the mean or median.
In 1st PUC Economics (Statistics), mean deviation measures the spread of data around a central value. It is calculated by taking the deviation of each item from the mean (or median), ignoring the plus/minus signs (taking only the absolute values), adding them up, and dividing by the number of items. Because it uses every observation, it is a better measure of dis …
- CBSE 2020Set ANNUAL1 markMCQQ.Mean deviation is calculated from-(a) Mean(b) Median(c) Mode(d) All of the above
›Reveal solutionSolution
Mean deviation can be calculated from all of the above — option (d).
Mean deviation is the average of the absolute deviations of the items from a central value. That central value can be the mean, the median or the mode. (In practice, mean deviation from the median is the least, but it can be computed fr …
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