Name That Medium >>

In the 1970s, almost all music was sold on vinyl records. Today, very few children even know what a record is, since vinyl accounts for less than 0.5% of all music sales. The following table lists the percent of sales from cassettes and CDs from 1990 through 2000. The table also includes the total income of the U.S. sound recording industry in each of those years.

(a) Ask students what trends they notice in the table, then have them draw a double line graph to compare the percent of cassette sales with the percent of CD sales over the eleven-year period. What kinds of predictions can they make about the future of the industry based on this graph? What other factors are not included in this graph that need to be considered when predicting future sales?

(b) Have older students find equations for lines of best fit for CD sales and for cassette sales. What do the slope and y-intercept of each equation represent? What are the coordinates of the point of intersection of the two graphs? What does the intersection point show?

(c) Have students explore the areas of music sales that are not shown in the table (including vinyl records, singles, and music videos). They can create an extra column in the table that represents "percent of sales other than cassettes or CDs," compare the market shares of each group, and represent their findings in a circle graph.

(d) Have students calculate the actual dollar amounts spent on cassettes and CDs over this period using calculators or spreadsheets. What trends do they notice about the "Total Sales" line over time?

2. Teachers Notes: Name That Medium

(a) Sales of CDs have clearly overtaken the sales of cassettes over the past decade. Internet downloads, such as MP3 usage, are not included in this chart. The disparity in cost between CDs and cassettes may influence market share percents, as well.

(b) The equation for the linear-regression model for cassettes is approximated by y = -5.05x + 53.3, whereas the best fit for CD sales is approximated by y = 5.5x + 34.2 (x represents the year; 1990 is represented by 0, and so on). The y-intercept tells roughly what percent of sales came from that source in the first year; the slope represents the change in percent of sales per year. While cassette sales were declining by an average of 5.05% per year, CD sales revenues increased an average of 5.5% per year. The intersection point of these two lines is approximately located at the coordinates (1.8, 44.2), which implies that late in 1991, the revenue generated from CD and cassette sales were equal--each accounting for about 44% of the market. Looking at the graphs of the lines of best fit, students can see that after that point, CDs began to surpass cassettes in sales.

(c) About 10% of all music sales have consistently come from a source other than CDs and cassettes.

(d) Although the total sales have almost doubled since 1990, increases have not occurred every year. Revenues from sales of music declined, for example, between 1996 and 1997 and between 1999 and 2000.

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