# Direct and Indirect standardisation. Flashcards

1
Q

If a rate is described as ‘crude’ what has not happened to it?

A

2
Q

What makes it difficult to compare crude rates of mortality between populations?

A

Factors related to mortality may be distributed differently between the two populations.

3
Q

Apart from standardisation how can you compare two crude rates that have different distributions of underlining factors?

A

Comparison of stratum specific rates.

4
Q

What are the steps of direct standardisation (3 steps) ?

A
1. Select a standard population.
2. Obtain the proportion of person-time (or people) in each stratrum of the selected standard population.
3. Compute a weighted average of the stratum–specific measures in each population in order to combine stratum specific rates into a single measure.
5
Q

In order to carry out direct standardisation what do you need to know about the standard and studies population?

A
1. The distribution of the variable in the standard population.
2. Stratum specific rates of the study populations.
6
Q

The sum of what produces the incidence rate (in direct standardisation)?

A

(Rate in stratum l in population P)(Proportion of person time in stratum l in the standard population S). Sum for all stratums.

7
Q

The sum of what produces the incidence proportion/risk (in direct standardisation)?

A

(Risk in stratum l in population P)(Proportion of person time in stratum l in the standard population S). Sum for all stratums.

8
Q

Why do you not need to state a confidence interval in a standardised rate calculation?

A

As all the data has been included.

9
Q

Although in theory any population can be used in direct standardisation, what population(s) should you use?

A

Standard populations that include all study populations.

10
Q

Where can you obtain artificially created populations to use for direct standardisation?

A

WHO.

11
Q

What is the standard mortality ratio?

A

SMR= Observed events/ Expected events (if the study population had the same rates as the standard)

12
Q

What do you need to know to carry out indirect standardisation?

A
1. Known stratum specific rates in the standard population.

2. Known distribution of the variable in the study populations.

13
Q

What does a SMR of 1 mean?

A

There is no difference in observed events/expected events between the standard population and study populations.

14
Q

What does a SMR of >1 mean?

A

Less events in the study population than expected.

15
Q

What does a SMR<1 mean?

A

More events in the study population than expected.

16
Q

When would you use indirect standardisation over direct standardisation?

A

When the number of events are low.

17
Q

Does direct or indirect standardisation apply the stratum specific rates to the study population from the standard population?

A

Indirect.

18
Q

Does direct or indirect standardisation apply the stratum specific rates to the standard population from the study population?

A

Direct.

19
Q

What can you not investigate with standardisation?

A

The factor you have standardised for.

20
Q

Standard rates are summary measures. This can mask what in your data?

A

Trends/ differences in stratum specific rates which could be interesting.

21
Q

What type of standardisation allows for multiple comparisons to be made?

A

Direct.

22
Q

Do you need to know the overall crude rate of the entire population in direct standardisation?

A

No. This is an advantage of direct standardisation.

23
Q

What are two disadvantages of direct standardisation?

A
1. Changing the standard population might change the conclusion made.
2. High numbers of events required for stable age-specific rates.
24
Q

You do not need to know the overall crude rate in direct standardisation, however you do in indirect standardisation. What do you not need to know in indirect standardisation?

A

Stratum specific counts in standard population.

25
Q

Can indirect or direct standardisation be estimated with poisson regression?

A

Indirect.

26
Q

Why is indirect standardisation preferable when populations are small?

A

Greater precision than direct standardisation. Lower counts can result in unstable estimates.

27
Q

Is it easier to compare SMR’s with direct or indirect standardisation?

A

Direct.

28
Q

When are standardised rates useful?

A

When you want to make comparisons between populations or across time periods.

29
Q

Why can using the same standard populations consecutively over many years be problematic?

A

The standard populations may change over time which would result in the different rates.

30
Q

Standard populations should represent all study populations equally. True or False?

A

False. It can represent them differently as long as it makes sense.