Open-end classes:
Open-end classes, also known as open-ended classes or open classes, are a type of classification system used in statistics and data analysis. In open-end classes, the lower limit of the first group and the upper limit of the last group are left undefined or open-ended. This means that the first group does not have a lower boundary and the last group does not have an upper boundary.

Explanation:
To understand why the lower limit of the first group and the upper limit of the last group are undefined in open-end classes, let's consider an example. Suppose we are categorizing the heights of individuals into different groups. We want to create groups of 10 cm each, starting from the height of 150 cm.

In a close-end class system, we would define the lower and upper limits for each group. For example:
- Group 1: 150 cm - 159.9 cm
- Group 2: 160 cm - 169.9 cm
- Group 3: 170 cm - 179.9 cm
and so on.

However, in an open-end class system, we leave the lower limit of the first group and the upper limit of the last group undefined. The groups would be defined as follows:
- Group 1: No lower limit - 159.9 cm
- Group 2: 160 cm - 169.9 cm
- Group 3: 170 cm - 179.9 cm
and so on.

Advantages of open-end classes:
There are several advantages to using open-end classes in data analysis:
1. Flexibility: Open-end classes allow for flexibility in data categorization. This is especially useful when dealing with data that has a wide range or when the exact boundaries for grouping are not known in advance.
2. Accommodating outliers: Open-end classes can easily accommodate outliers or extreme values that fall outside the defined boundaries of other groups. These outliers can be included in the first or last group without disrupting the overall classification.
3. Simplified analysis: Open-end classes can simplify data analysis by reducing the number of groups and making it easier to interpret the results. This is particularly beneficial when presenting data to a non-technical audience.

Conclusion:
In open-end classes, the lower limit of the first group and the upper limit of the last group are left undefined. This provides flexibility, accommodates outliers, and simplifies data analysis. Open-end classes are a useful classification system in statistics and data analysis.