Epi in the News

Thanks so much

Interesting read... flouride and teeth have always been a controversial combination- nobody really can tell whats the limit after which it shifts from beneficial to harmful..

1) Interesting question. Initially I did think like Sam - a prevalence figure.. thinking that the authors are just reporting how many children were detected to have tooth decay. But then reading the sentence again, it could be incidence as well- because its mentioned that in the 2019 school year, this percentage experienced damage to their teeth (that could mean new damage as well). Its not clear... as long as its not clear, we would have to think its prevalence (number with damage/ total number in the 2019 school year ).
2) The more appropriate term would be "risk". Again the reported is not good- they are using the term rate but without specifying the denominator or the time factor.
3) So this calculation would be by calculating the risk ratios (risk of damage with fluoride added/ risk of damage without fluoride). The RR for the rich would be 0.83 and for the poor it will be RR 0.72.
From the wordings it look like they are talking about ratios rather than risk difference.
4) In this case, the exposure is reducing the risk- so we have to think in terms of preventive fraction- how much of the disease is prevented because of the exposure. And this is given by (1-RR). So, the article essentially states the preventive fraction- in the rich 17% of cavities prevented due to fluoride, and 28% for the poor.

Very interesting read.

1. I think that it is prevalence figure calculated as the number of children of a specific age with dental damage in the 2019 school year in a specified geographical location / total number of children of the specific age range over the same time period and location.

2. Risk

3. He may have calculated the risk ratio for dental damage for fluoride added to no fluoride added in the rich and same in the poor, then subtracted from 1 and expressed as a percentage

4. Preventative fraction

1. Prevalence figure. Numerator: 5-year olds (or 4-5year old children in Scotland) with tooth decay. Denominator: population of 5-year old children in the regions mentioned in the 2019 school-year.

2. Risk

3. Risk of tooth decay in those with access to fluoridated water/ risk of tooth decay in those without access to fluoridated water by socioeconomic status (rich and poor). Risk ratio as a fraction (%) is reported.

4. Preventable fraction

Thank you Sujit for the article and thank you to all those who have replied.

I agree with you about questions 1 and 2.

I struggled with 3 and 4,"among the richest.... and among the poorest children" makes it sound as if this is an attributable risk and that Chris Whitty was taking the percentage of rich (or poor) children who currently have cavities and subtracting the percentage he thought would have cavities if fluoride were added to water supplies and that the difference was 17% in the richest and 28% in the poorest children.

I had a look at the statement here,

https://www.gov.uk/government/publications/water-fluoridation-statement-from-the-uk-chief-medical-officers

and this refers to an earlier piece of work here,

https://www.gov.uk/government/publications/water-fluoridation-health-monitoring-report-for-england-2018

and I do think that he is referring to an attributable risk. Please put me straight if you disagree!

Best wishes

Judith

Good morning Sujit,
Although I might not have went through the appropriate chapters yet, I want to check what I already want.
1. They mention that it happened in the 2019 school year, so this should be incidence. Numerator is number of 5 year olds in England or 4-5 year olds in Scotland who had experienced damage to their teeth in 2019 school year, denominator should be number of 5 year olds in England or 4-5 year olds in Scotland who are attending school in the 2019 school year
2. Prevalence
3. We need the definition of "poorest" and "richest", and the case definition of "reduce cavities", and to check the incidence of cavities in the year before the fluoride was added then the incidence in the year after fluoride was added for each respective population, then calculate the reduction by deducting the new incidence from old incidence then divide by the old incidence.

1. This is, in most likely case, an incidence figure.
The numerator is number of five-year-olds in England or four- to five-year-olds in Scotland who had experienced damage to their teeth in the 2019 school year, and the denominator is the total number of five-year-olds in England or four- to five-year-olds in Scotland (at risk population) at the beginning of the 2019 school year.
2. Risk.
3. Chris Whitty stratified the data according to socio-economic status, i.e. richest and poorest children. Then he calculated the population attributable risk for richest children and poorest children separately.
4. Effect modification or interaction.