Child Development

5.5.06

www.healthforallchildren.com - Parents' page - plot child's growth.

Lines on charts are centiles - based on normal.

50th centile
• 50% of normal children below, 50% above.

2nd centile
• 2% of normal children below, 98% normal.
• Is small child normal or abnormal?

Surveillance about watching (i.e. over time)
• Does child follow centile or cross-centiles?

Sometimes also used as cross-sectional assessment of growth, "screening" separating out those who are probably normal.

Developmental norms are developed empirically.

Regression
• "Given data of a dependent variable y and one or more independent variables x1, x2 etc. Regression analysis involves finding the best mathematical model to describe y as a function of the 'x's."
• Will see it used in many papers.
• Regression used to:
-Describe relationship between variables.
-Predict outcome from set of risk factors.
-"Adjust" for known confounder.
• Interpretation of coefficient depends on model.
• Can be:
-Linear (single or multiple).
-Logistic (probably commonest).
-Proportional hazards.
• Logistic regression estimates odds ratios.
• Will see these terms in papers you read.
• Linear regression different from correlation.

Correlation coefficient: "A measure of association that indicates the degree to which two variables have a linear relationship. This coefficient, represented by the letter 'r', can vary between +1 and -1; when r= +1, there is a perfect positive linear relationship in which one variable varies directly with the other; when r+ -1, there is a perfect negative linear relationship between the variables."

Scenario - notifications?
• Of infectious diseases.
• Commenced end of 19th Century - 1891 in London, 1899 elsewhere.
• List of diseases increased over time - now stands at around 30.
• Originally, head of family or landlord's responsibility to local Proper Officer.
• Now, attending medical practitioner, either in patient's home, surgery or hospital.
• Proper Officer = CCDC.

Purpose of notification
• To detect possible outbreaks of epidemics.
-Accuracy of diagnosis secondary.
• Statistics of collected rationally at Registrar General's office.
• In 1997, responsibility for administering NOIDs system transferred to Communicable Disease Surveillance Centre, now HPA.

Epidemic precipitates investigation, in order to:
• Determine source and mode of transmission.
• Interrupt chain of transmission (control measures).
• Prevent secondary spread.
• Prevent other outbreaks under similar circumstances.

Steps in investigation
1. Confirm diagnosis.
2. Set case definition.
3. Describe case by person, time and place.
4. Formulate and test hypothesis.
5. Undertake any additional methods to control outbreak.
6. Evaluate measures taken.
7. Report on handling of outbreak and its control to various authorities.

Patterns of epidemic
• May start from Common (Point) Source - with all cases exposed at same time to one source of infection.
• In contagious epidemic, disease passed from person to person.
• Slow rise in number of cases.

Prevention paradox?
• Preventive measure bringing large benefit to community, but may offer little to most participating persons.
-Eg. immunisation.
- Why is paradox problem for NHS?
• People motivated by benefit which is visible, early and likely.

Infectious disease epidemiology
• Health promotion.
-Disease prevention.
§Primary - immunisation.
§Secondary - limiting spread.