🔢 Summarizing Data: Number of Observations

Learning goal: I can summarize a data set by reporting the number of observations (n).

Language goal: I can state how many data values were collected using the phrase there are ___ observations.

📚 Vocabulary

Observation: A single recorded data value (one measurement or response).

Number of observations (n): How many data values are in the set.

Data set: The whole collection of observations.

When you summarize data, the first thing to report is how many values you have. We call this the number of observations, written n.

In a list, count every value (including repeats). In a dot plot, count every dot. In a survey, it's the number of responses.

Example: the scores {88, 92, 75, 90, 85} have n = 5 observations.

Worked example. How many observations are in {88, 92, 75, 90, 85} ?

Score: 0 / 4

1. How many observations are in {3, 7, 7, 2, 9, 4} ?

💡 Count every value, including the repeated 7.

2. A survey asked 12 households how many pets they own. What is n?

💡 n is the number of responses.

3. A dot plot shows these dots above the numbers: 2 dots on 4, 3 dots on 5, 1 dot on 7. How many observations?

💡 Add up all the dots: 2 + 3 + 1.

4. The number of observations tells you…

💡 n counts the data, it does not summarize size.

A class recorded {6, 8, 6, 10, 9, 7, 8}. State the number of observations and explain what n means.