Arithmetic Mean
The arithmetic mean (or simply "mean") of a sample is the sum of the sampled values divided by the number of items in the sample.
Merits of Arithmetic Mean
- Arithmetic mean is rigidly defined by an algebraic formula.
- It is easy to calculate and simple to understand.
- It is based on all observations and can be regarded as representative of the given data.
- It is capable of being treated mathematically and hence it is widely used in statistical analysis.
- Arithmetic mean can be computed even if the detailed distribution is not known but some of the observations and the number of observations are known.
- It is least affected by the fluctuation of sampling.
Demerits of Arithmetic Mean
- It can neither be determined by inspection nor by graphical location.
- Arithmetic mean cannot be computed for qualitative data like data on intelligence, honesty, and smoking habits, etc.
- It is too much affected by extreme observations and hence it does not adequately represent data consisting of some extreme points.
- Arithmetic mean cannot be computed when class intervals have open ends.
Median
The median is that value of the series which divides the group into two equal parts, one part comprising all values greater than the median value and the other part comprising all the values smaller than the median value.
Merits of Median
- Simplicity: It is a very simple measure of the central tendency of the series. In the case of simple statistical series, just a glance at the data is enough to locate the median value.
- Free from the effect of extreme values: Unlike arithmetic mean, median value is not destroyed by the extreme values of the series.
- Certainty: Certainty is another merit of the median. Median values are always a certain specific value in the series.
- Real value: The median value is a real value and is a better representative value of the series compared to the arithmetic mean (average), the value of which may not exist in the series at all.
- Graphic presentation: Besides algebraic approach, the median value can be estimated through graphic presentation of data as well.
- Possible even when data is incomplete: Median can be estimated even in the case of certain incomplete series. It is enough if one knows the number of items and the middle item of the series.
Demerits of Median
Following are the various demerits of median:
- Lack of representative character: Median fails to be a representative measure in case of such series where the different values are wide apart from each other. Also, median is of limited representative character as it is not based on all the items in the series.
- Unrealistic: When the median is located somewhere between the two middle values, it remains only an approximate measure, not a precise value.
- Lack of algebraic treatment: Arithmetic mean is capable of further algebraic treatment, but median is not. For example, multiplying the median with the number of items in the series will not give us the sum total of the values of the series.
However, median is quite a simple method for finding an average of a series. It is quite a commonly used measure in the case of such series which are related to qualitative observations such as the health of the student.
Mode
The value of the variable which occurs most frequently in a distribution is called the mode.
Merits of Mode
Following are the various merits of mode:
- Simple and popular: Mode is a very simple measure of central tendency. Sometimes, just looking at the series is enough to locate the modal value. Because of its simplicity, it is a very popular measure of the central tendency.
- Less effect of marginal values: Compared to the mean, mode is less affected by marginal values in the series. Mode is determined only by the value with the highest frequency.
- Graphic presentation: Mode can be located graphically, with the help of a histogram.
- Best representative: Mode is that value which occurs most frequently in the series. Accordingly, mode is the best representative value of the series.
- No need of knowing all the items or frequencies: The calculation of mode does not require knowledge of all the items and frequencies of a distribution. In simple series, it is enough if one knows the item with the highest frequency in the distribution.
Demerits of Mode
Following are the various demerits of mode:
- Uncertain and vague: Mode is an uncertain and vague measure of the central tendency.
- Not capable of algebraic treatment: Unlike mean, mode is not capable of further algebraic treatment.
- Difficult: When the frequencies of all items are identical, it is difficult to identify the modal value.
- Complex procedure of grouping: Calculation of mode involves cumbersome procedure of grouping the data. If the extent of grouping changes, there will be a change in the modal value.
- Ignores extreme marginal frequencies: It ignores extreme marginal frequencies. To that extent, the modal value is not a representative value of all the items in a series. Besides, one can question the representative character of the modal value, as its calculation does not involve all items of the series.
Practice Problems: To Find Mean
- Below is given distribution of money (in Rs.) collected by students for flood relief fund. Find mean of money (in Rs.) collected by a student by 'Direct Method'.
- Following table gives age distribution of people suffering from 'Asthma' due to air pollution in a certain city. Find mean age of persons suffering from 'Asthma' by 'Direct Method'.
- The measurements (in mm) of the diameters of the head of screws are given below: Calculate mean diameter of head of a screw by 'Assumed Mean Method'.
- Below is given frequency distribution of marks (out of 100) obtained by the students. Calculate mean marks scored by a student by 'Assumed Mean Method'.
- The following table gives frequency distribution of milk (in litres) given per week by 50 cows. Find average (mean) amount of milk given by a cow by 'Shift of Origin Method'.
- The following table gives the frequency distribution of trees planted by different housing societies in a particular locality. Find the mean number of trees planted per housing society by using the 'step deviation method'.
- The following table gives age distribution of people suffering from 'Asthma' due to air pollution in a certain city. Find the mean by the 'Step Deviation method'.
- The measurements (in mm) of the diameters of the head of screws are given below: Find the mean by 'Step deviation method'.
- Solve by the 'Assumed Mean method'. The following table gives the frequency distribution of trees planted by different housing societies in a particular locality. Find Mean.
- Solve by the 'Step Deviation Method'. Below is the frequency distribution of marks (out of 100) obtained by the students. Find mean.
Practice Problems: To Find Median
- Following is the distribution of the size of certain farms from a taluka (tehsil): Find median.
- Below is given distribution of profit (in Rs.) per day of a shop in certain town: Calculate median profit of a shop.
- Following table shows distribution of monthly expenditure (in Rs.) by households in a certain village on electricity: Find median expenditure done by a household on electricity per month.
- The following table shows ages of 300 patients getting medical treatment in a hospital on a particular day. Find median age of a patient.
Practice Problems: To Find Mode
- The weight of coffee (in g) in 70 packets is given below: Determine the modal weight of coffee in a packet.
- Forty persons were examined for their Hemoglobin % in blood (in mg per 100 ml) and the results were grouped as below: Determine modal value of Hemoglobin % in blood of a person.
- The maximum bowling speed (km/hour) of 33 players at a cricket coaching centre is given below: Find the mode.
- The following table shows frequency distribution of body weight (in g) of fish in a pond. Find modal body weight of a fish in a pond.
Relationship Between Mean, Median, and Mode
- For a certain frequency distribution the values of Mean and Mode are 54.6 and 54 respectively. Find the value of median.
- For a certain frequency distribution the values of Median and Mode are 95.75 and 95.5 respectively, find the mean.
- For a certain frequency distribution the value of Mean is 101 and Median is 100. Find the value of Mode.
ALSO REFER THESE ECONOMICS QUESTIONS.
Difficult Words & Meanings:
- Arithmetic Mean: The average of a set of numbers, found by summing all numbers and dividing by the count of numbers.
- Median: The middle value in a dataset that has been arranged in order of size.
- Mode: The value that appears most frequently in a dataset.
- Sample: A small part or quantity intended to show what the whole is like; a selection from a larger population.
- Values: The specific numbers or pieces of data in a set.
- Observations: The individual data points or values collected during a study or survey.
- Algebraic Formula: A mathematical rule or principle expressed in symbols or letters.
- Qualitative Data: Information that describes characteristics or qualities and cannot be easily measured with numbers (e.g., color, opinions, gender).
- Extreme Values/Observations: Data points that are significantly smaller or larger than other values in a dataset.
- Class Intervals: The ranges into which data is divided for grouping (e.g., 10-20, 20-30).
- Open Ends (Class Intervals): When the first class interval has no lower limit or the last class interval has no upper limit (e.g., "Under 10" or "50 and over").
- Central Tendency: A statistical measure that identifies a single value as representative of an entire distribution (e.g., mean, median, mode).
- Frequency: The number of times a particular value or event occurs in a dataset.
- Distribution: The way in which data or values are spread or arranged.
- Histogram: A graphical display of data using bars of different heights, where each bar groups numbers into ranges.
- Marginal Values/Frequencies: Values or frequencies that are at the outer edges or extremes of a dataset.
- Cumbersome: Complicated, slow, or difficult to do or use.
- Fluctuation: An irregular variation or change in level, amount, or value.
- Rigidly Defined: Clearly and precisely established, leaving no room for ambiguity.
- Inspection (statistical): The process of carefully examining data to identify patterns or features without complex calculations.
- Graphical Location: Determining a value by using a graph or chart.
- Representative Character: The extent to which a single statistical measure (like mean or median) accurately reflects the entire dataset.
- Approximate Measure: A value that is close to the actual value but not perfectly exact.
- Vague (measure): Not clearly or precisely expressed; indefinite.
- Identical (frequencies): Occurring when all values in a dataset have the same frequency (number of occurrences).