Standardised Mortality Ratios and Health Data (Lecture:Observational Studies and Routine Data)

Question 1

What are standardised mortality ratios?

Answer 1

Represents the ratio of the number of observed deaths (or cases of disease) (O) in a particular population to the number that would be expected (E), if that population had the same mortality or morbidity experience as a standard population, corrected for differences in age (and sex) structure.

‘standardised’ means that it takes into account/adjusts for factors such as age and sex so that you can compare the two areas fairly. e.g. one area may be full of old people and the other area may be full of children, you can’t compare the mortality rates of these two areas directly

Question 2

How are Standardised mortality ratios used?

Answer 2

• Life insurance companies adjust their premiums based on standardised mortality ratios
• Medical/epidemiological research. Eg helps focus spending of research

Question 3

What is routine data?

Answer 3

“Data that are routinely collected and recorded in an ongoing systematic way, often for administrative or statutory purpose and without any specific research question in mind at the time of collection”

i.e. these data are health data collected as it is required by law e.g. births, deaths. They are not collected for any research purposes.

Question 4

Examples of routine data?

No need to memorise list but you need to have an idea of what it is.

Answer 4

Healthcare use and outcome data e.g. hospital admissions, primary care consultations or prescriptions, immunisation uptake

Exposures and health determinant data, e.g., air pollution, crime statistics

Demographic data e.g. census

Geographical data e.g. location of GP practices

Health service provision, e.g. bed/staff counts

Births/Deaths

Cancer Registrations

Prescriptions

Road traffic accidents

Hospital admissions

Question 5

Advantages of routine data? (routine data are basically health data)

Answer 5

Relatively cheap

Already collected and available in the past so a lot of data available. Can be used to e.g. look at time trends (e.g. change in certain health factors as time goes by)

Standardised collection procedures

Relatively comprehensive – this means that it covers a large population of people/ large numbers rather than e.g. just the patients from a small hospital. (this is because these data are collected across the country)

Wide range of recorded items

Experience in use and interpretation (the practice of collecting these data has been going on for a long time so people are experienced in interpreting and using them)

Question 6

Disadvantages of routine health data?

Answer 6

May not answer the question (no information or not enough detail)- they were initially collected for legal purposes (required by law), not collected to answer your research questions

Incomplete ascertainment (not every case captured)

Variable quality between different hospitals

Validity may be variable (i.e. do they measure what you think they measure?)

Disease labelling may vary over time or by area

Coding changes may create artefactual increases or decreases in rates - Junior doctors write notes and these notes are then converted to codes (recognised internationally) that may indicate specific info about the condition of the patient. If these codes change, then the data will also be affected.

Need careful interpretation