Two sectors can only be compared on measures that match in unit, year and source. Converting each measure to a percentage share can make that possible.
This lesson is part of primary, secondary and tertiary activities. Value added is covered in tracing value added.
What must match before I compare?
Check three things: the unit, the year and the source. If any differs, a direct comparison is unsafe.
If they match, compare. If they do not, convert to shares or state that the comparison is not possible.
Worked example: jobs and output in an invented country
This is a worked example with invented figures for one year.
| Sector | Jobs (thousand) | Output (RM billion) |
|---|---|---|
| Primary | 600 | 40 |
| Secondary | 1 200 | 260 |
| Tertiary | 2 200 | 300 |
| Total | 4 000 | 600 |
Convert jobs to shares. Primary is 600 ÷ 4 000 = 15%. Secondary is 1 200 ÷ 4 000 = 30%. Tertiary is 2 200 ÷ 4 000 = 55%.
Convert output to shares. Primary is 40 ÷ 600 = 6.7%, about 7%. Secondary is 260 ÷ 600 = 43.3%, about 43%. Tertiary is 300 ÷ 600 = 50%.
Now compare the matched shares. Secondary provides 30% of jobs but 43% of output, whereas primary provides 15% of jobs but only 7% of output.
A full sentence: “Secondary provides 43% of output from 30% of jobs, so output per worker is higher than in primary, which gives 7% of output from 15% of jobs.”
The mistake that loses marks
The wrong step is to set 2 200 thousand jobs beside RM300 billion and say “tertiary is bigger in both”. The two numbers have different units.
| Step | Wrong | Right |
|---|---|---|
| Compare | 2 200 jobs vs RM300 billion | 55% of jobs vs 50% of output |
| Conclusion | Tertiary dominates everything | Tertiary has a larger job share than output share |
The right version shows something new: tertiary has slightly more of the jobs than output, while secondary is the reverse.
What can I conclude, and what not?
You can say secondary output per worker is higher than primary. You cannot say why from these figures alone. Machines, skills and prices may all play a part.
Mark the limit: “The table does not show the cause of the difference.” A second limit is that one year cannot show a trend. The graph evidence and fair-comparison lab gives a structure for writing these limits.
Check yourself
In another invented country, jobs are primary 200, secondary 300, tertiary 500 (thousand). Output is primary RM10 billion, secondary RM60 billion, tertiary RM30 billion. Compare the secondary job share and output share.
Answer
Jobs total 1 000, so secondary is 300 ÷ 1 000 = 30%. Output totals 100, so secondary is 60 ÷ 100 = 60%.
Secondary provides 60% of output from 30% of jobs, which means its output per worker is about twice the average. The data does not show why.
What to study next
Test the whole topic with the topic practice set. For a teacher to go through your conversions with you, see online one-to-one Geography tuition.