<p>A little background.  The paper relates to a tax (known as the Soft Drinks Industry Levy) introduced by the UK in 2018 on some soft drinks, levied on manufacturers (not consumers), with the aim, <a href="https://www.gov.uk/government/publications/soft-drinks-industry-levy/soft-drinks-industry-levy#policy-objective" rel="noreferrer">according to the government</a>, of encouraging manufacturers to reduce the sugar content of drinks and reduce portion sizes of added sugar drinks, and so contribute to reducing childhood obesity.</p>
<p>As explained in the paper, soft drinks are divided for the purposes of the tax into 4 (not 3) categories:</p>
<ul>
<li>Levy exempt drinks, exempt from the levy irrespective of their sugar content, including 100% fruit juices and drinks that are mostly milk;</li>
<li>High tier drinks, not exempt as above and containing &gt; 8g sugar per 100 ml;</li>
<li>Low tier drinks, not exempt as above and containing 5-8g sugar per 100 ml;</li>
<li>No levy drinks, not subject to the levy because with &lt; 5g sugar per 100 ml.</li>
</ul>
<p>The results in the paper are statistical estimates based on sample data from a panel of households.  They are mostly quoted in the form of a central estimate followed by a 95% confidence interval.   From the Results section of the paper (rather than the Abstract) we can find the following estimates for volume changes:</p>
<p>Levy exempt drinks:  No statistically significant change in overall purchase volume.</p>
<p>High tier drinks: Reduction of 139.0 mL (central estimate) with confidence interval from -86.9 to -191.0.</p>
<p>Low tier drinks:  Reduction of 177.3 mL (central estimate) with confidence interval from -129.3 to -225.3.</p>
<p>No levy drinks: Increase of 210.5 mL (central estimate) with confidence interval from -100.1 to +521.2.</p>
<p>The three quoted central estimates sum to -105.8 mL.  <em>Prima facie</em>, this is as the OP suggests inconsistent with the statement (in the paragraph headed Secondary Analysis: all soft drink categories combined) that there was no change observed in the purchase volume of all soft drinks.  However, two points need to be considered.  Firstly, the sum above excludes any change in volume of levy exempt drinks.  To say that there was no statistically significant change does not imply that there was no change: it may just be that, from the study data, a null hypothesis of no change could not be rejected at a 5% significance level.  Secondly, the quoted confidence intervals, especially that for no levy drinks, are very wide, suggesting that the central estimates should be treated with considerable caution, and that a total obtained by summing the central estimates may not be very meaningful.</p>

CC BY-SA 4.0
2021-06-20T07:01:09.183Z
thank you. I see what you mean. So if I am trying to present an analysis of this article, and extrapolate some data points from the article, this is not possible. E.g. analysing the economics of this sugar tax and drawing a supply and demand curve with various shifts etc. AND I want to include some data from the article (rather than letter variables), this is not possible?
Rushi
CC BY-SA 4.0
2021-06-20T21:58:03.050Z
@Rushi  That's quite a broad supplementary question, and I'll just make a couple of observations in response.  1) Unless I've missed something the paper contains no data or results on prices, so it's hard to see how supply or demand curves could be inferred from it.  2) I would be very cautious about extrapolating from results which are just statistical estimates and subject to such wide confidence intervals.
Adam Bailey
CC BY-SA 4.0
2021-06-19T22:07:48.717Z
2021-06-19T22:07:48.717Z
Adam Bailey
<p>The research paper <a href="https://www.bmj.com/content/372/bmj.n254#:%7E:text=Intervention%20A%20two%20tiered%20tax,taxed%20at%20%C2%A30.18%2FL." rel="nofollow noreferrer">Changes in soft drinks purchased by British households associated with the UK soft drinks industry levy: controlled interrupted time series analysis</a> was examining the impact of the sugar tax in Britain.</p>
<p>In particular, the researchers of that BMJ paper found that whilst the <strong>volume</strong> of soft drinks sold remained the same the quantity of sugar consumed fell by 10% as a result of reformulation.</p>
<p>However, when you read the finer details, we are told the following:</p>
<ul>
<li>For soft drinks containing less than 5g/100ml: volume sold - no change.</li>
<li>&quot; 5g-8g/100ml: volume sold decreased by 86%</li>
<li>&quot; &gt;8g/100ml: volume sold decreased by 44%</li>
</ul>
<p>How, then, can the total volume of soft drinks sold not have changed?</p>

CC BY-SA 4.0
2021-06-18T21:25:22.120Z
Can you please link to those articles? Possibly journalists misread the scientific article please link both to news article and paper itself
1muflon1
CC BY-SA 4.0
2021-06-19T08:47:12.460Z
@1muflon1 - Thank you for raising a relevant point. I believe another user has now linked the paper in the question. The news article was: https://news.sky.com/story/sugar-tax-consumption-of-sugar-from-soft-drinks-falls-by-10-12242372
Rushi
CC BY-SA 4.0
2021-06-19T16:32:43.733Z
@1muflon1 - any luck, good sir?
Rushi
<microeconomics><taxation><public-economics><externalities>
Understanding an article in the BMJ about the sugar tax
Rushi
# Understanding an article in the BMJ about the sugar tax

(Asked by: username_0 on 2021-06-18)

The research paper [Changes in soft drinks purchased by British households associated with the UK soft drinks industry levy: controlled interrupted time series analysis](https://www.bmj.com/content/372/bmj.n254#:%7E:text=Intervention%20A%20two%20tiered%20tax,taxed%20at%20%C2%A30.18%2FL.) was examining the impact of the sugar tax in Britain.

In particular, the researchers of that BMJ paper found that whilst the **volume** of soft drinks sold remained the same the quantity of sugar consumed fell by 10% as a result of reformulation.

However, when you read the finer details, we are told the following:

* For soft drinks containing less than 5g/100ml: volume sold - no change.
* " 5g-8g/100ml: volume sold decreased by 86%
* " >8g/100ml: volume sold decreased by 44%

How, then, can the total volume of soft drinks sold not have changed?

**Tags:** microeconomics, taxation, public-economics, externalities
> **Comments:**
> **username_1**: Can you please link to those articles? Possibly journalists misread the scientific article please link both to news article and paper itself  
> **username_0**: @1muflon1 - Thank you for raising a relevant point. I believe another user has now linked the paper in the question. The news article was: https://news.sky.com/story/sugar-tax-consumption-of-sugar-from-soft-drinks-falls-by-10-12242372  
> **username_0**: @1muflon1 - any luck, good sir?  

---

## 1 answers

### Answer by username_2 on 2021-06-19. Score: 5 | Accepted answer

A little background. The paper relates to a tax (known as the Soft Drinks Industry Levy) introduced by the UK in 2018 on some soft drinks, levied on manufacturers (not consumers), with the aim, [according to the government](https://www.gov.uk/government/publications/soft-drinks-industry-levy/soft-drinks-industry-levy#policy-objective), of encouraging manufacturers to reduce the sugar content of drinks and reduce portion sizes of added sugar drinks, and so contribute to reducing childhood obesity.

As explained in the paper, soft drinks are divided for the purposes of the tax into 4 (not 3) categories:

* Levy exempt drinks, exempt from the levy irrespective of their sugar content, including 100% fruit juices and drinks that are mostly milk;
* High tier drinks, not exempt as above and containing > 8g sugar per 100 ml;
* Low tier drinks, not exempt as above and containing 5-8g sugar per 100 ml;
* No levy drinks, not subject to the levy because with < 5g sugar per 100 ml.

The results in the paper are statistical estimates based on sample data from a panel of households. They are mostly quoted in the form of a central estimate followed by a 95% confidence interval. From the Results section of the paper (rather than the Abstract) we can find the following estimates for volume changes:

Levy exempt drinks: No statistically significant change in overall purchase volume.

High tier drinks: Reduction of 139.0 mL (central estimate) with confidence interval from -86.9 to -191.0.

Low tier drinks: Reduction of 177.3 mL (central estimate) with confidence interval from -129.3 to -225.3.

No levy drinks: Increase of 210.5 mL (central estimate) with confidence interval from -100.1 to +521.2.

The three quoted central estimates sum to -105.8 mL. *Prima facie*, this is as the OP suggests inconsistent with the statement (in the paragraph headed Secondary Analysis: all soft drink categories combined) that there was no change observed in the purchase volume of all soft drinks. However, two points need to be considered. Firstly, the sum above excludes any change in volume of levy exempt drinks. To say that there was no statistically significant change does not imply that there was no change: it may just be that, from the study data, a null hypothesis of no change could not be rejected at a 5% significance level. Secondly, the quoted confidence intervals, especially that for no levy drinks, are very wide, suggesting that the central estimates should be treated with considerable caution, and that a total obtained by summing the central estimates may not be very meaningful.

> **Comments:**
> **username_0**: thank you. I see what you mean. So if I am trying to present an analysis of this article, and extrapolate some data points from the article, this is not possible. E.g. analysing the economics of this sugar tax and drawing a supply and demand curve with various shifts etc. AND I want to include some data from the article (rather than letter variables), this is not possible?  
> **username_2**: @Rushi  That's quite a broad supplementary question, and I'll just make a couple of observations in response.  1) Unless I've missed something the paper contains no data or results on prices, so it's hard to see how supply or demand curves could be inferred from it.  2) I would be very cautious about extrapolating from results which are just statistical estimates and subject to such wide confidence intervals.  

---

