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Flashcards · 0479 · Topic 9
Crude and standardised rates flashcards
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Topic 9: Crude and standardised rates
- How is a crude birth rate or crude death rate calculated?
- Number of births (or deaths) ÷ total population × 1000, giving a rate per thousand people. The question defines the rate it wants, so use its definition.
- An island has 52 000 people and 936 births in a year. Find the crude birth rate
- 936 ÷ 52 000 × 1000 = 18.0 per thousand.
- How does the denominator of a fertility rate differ from a crude birth rate?
- A fertility rate usually divides births by the number of women in a stated age range (per thousand women), not by the whole population. Check the definition given in the question.
- What is an age-specific (subgroup) rate?
- Events in one group ÷ people in that group × 1000. The group can be an age band, a sex, an occupation or years of driving experience.
- Why is a standardised rate calculated?
- Event rates depend on age, and populations differ in age structure, so crude rates may not compare like with like. A standardised rate removes the effect of population make-up.
- How do you calculate a standardised rate?
- Standardised rate = Σ(standard population of group × group rate) ÷ Σ(standard population). It is a weighted mean of the subgroup rates, weighted by the standard population, which the question supplies.
- A standard population is 40% under 50 and 60% aged 50 and over. A town has death rates of 4 and 10 per thousand. Find the standardised rate
- (40 × 4 + 60 × 10) ÷ 100 = 760 ÷ 100 = 7.6 per thousand.
- Why is the plain mean of the group rates not the standardised rate?
- A plain mean treats every group as equally common. The standardised rate weights each group by the size of that group in the standard population.
- How do you find the number of events from a rate?
- Number of events = rate × population ÷ 1000. Example: crude birth rate 12.5 per thousand in 240 000 people → 3000 births.
- A town's crude death rate is much higher than its standardised rate. What does that suggest?
- The town has a larger share of older people than the standard population, which pushes its crude rate up.
- Is a standardised rate the actual rate in the population?
- No. It is a measure for fair comparison, and its value depends on which standard population was used.