How many cases were there?

My interest is always piqued as soon as a news report refers to rates of some disease being “on the rise”.  I’m usually disappointed as I wait to hear the details since often no actual numbers are provided.

Last week a CKOM news brief declared “Heterosexual sex HIV transmission on rise in Sask“.  Really? No details are provided, just quotes from an AIDS Saskatoon coordinator.

What are the actual numbers?*                    2009        2010        2011        2012        2013

Total HIV cases                                                  94            74             66            55              43

Heterosexual sex transmission                   12            11             12             13               9

Injection drug use transmission**            76            56             49             34             28

 

The total number of new HIV cases in the health region is falling and this decrease is primarily among injection drug users.  When the percent of cases associated with one cause decreases, the other causes increase as a percent of the total.  In 2009, 81% of HIV transmission was via IDU and 12% from heterosexual sex compared to 65% and 21% respectively in 2013.

Conclusion?  Heterosexual HIV transmission in the Saskatoon Health Region is not increasing.  A larger percentage of cases are the result of heterosexual sexual contact but there are a smaller number of cases.

I also noted that 68% of cases had heterosexual contact with an injection drug user and 30% of cases had sexual contact with a confirmed or suspected HIV+ person.

*Information from the Saskatoon Health Region’s “HIV Strategy Report 2012-2013” and “Better Health for All Series 5: Rates of HIV declining but more needs to be done“.

** Could be +/- 1 since I used a graph to estimate the percentage in each category.

 

 

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How many sexual assaults each year?

A round table topic on The Sara Mills Show yesterday was the under-reporting of sexual assaults.  One of the guests said that only 3 of every 1000 sexual assaults resulted in a conviction.  That number seemed really low so I asked about it.  The source is an infographic produced by the YWCA and highlighted in a Huffington Post article.

o-SEXUAL-ASSAULT-CANADA-570

Where did that 460,000 number come from?  How do you count sexual assaults that aren’t reported?

The source cited is the chapter “Limits of a Criminal Justice Response: Trends in Police and Court Processing of Sexual Assault” by Holly Johnson in the book Sexual Assault in Canada: Law, Legal Practice and Women’s Activism, edited by Elizabeth Sheehy and published in 2012.

Where did she get the number?

Her source was the 2004 General Social Survey (Victimization)conducted by Statistics Canada.  A summary is available.  The question asked was “During the past 12 months, has anyone ever touched you against your will in any sexual way?  By this I mean anything from unwanted touching or grabbing, to kissing or fondling.”

So, 460,000 is an estimate of “sexual assault” calculated based on a survey of ~24,000 people and includes unwanted touching, grabbing, kissing, or fondling.  Is it any wonder that these “assaults” are not reported?

The truth is that we don’t know how many sexual assaults go unreported because they are not reported.  Based on the overly broad definition used above, it’s safe to say that the number is much less than 460,000 per year.  Exaggerating doesn’t strengthen your point; it weakens your position because your audience won’t trust your other “facts”.

 

 

Running for life?

In this week’s health news, running will make you live longer.  Maybe.  Maybe not.

The National Post headline announced that  “Running for five to 10 minutes a day may add three years to lifespans, study suggests“(7/29/2014).  I shouldn’t blame the journalists for exaggerating when the journal article title oversells the study findings as well:  Leisure-Time Running Reduces All-Cause and Cardiovascular Mortality Risk.  (Lee D, Pate RR, Lavie CJ, Sui X, Church TS, Blair SN. J Am Coll Cardiol 2014; 64:472-81.)

The study basics:

  • subjects = 55,137 people who visited a health clinic for a check-up between 1974 and 2002; mostly white, middle to upper class, college educated
  • Data was gathered at the first visit and, where possible, at a second visit whenever that might have occurred.
  • National Death Index used to identify death through 2003.
  • Running was self-reported estimate of activity over previous six months including frequency, duration, distance and speed.

 All of the graphs in the paper illustrate differences in hazard ratio (risk of death in one group compared to another group) rather than differences in actual mortality rates.  The paper provides mortality rates adjusted for baseline age, sex, and examination year so I’ve graphed those rates for comparison.

running and mortality bar chart

We can make predictions based on this information.  Each person-year is observing one person for one year.  So 10,000 person-years could be following 10,000 people for one year, 5,000 people for two years, 1,000 people for ten years or some other combination.  Comparing a group of 10,000 non-runners to a group of 10,000 runners, you would expect to observe 15 more deaths in the non-running group (45 vs. 30).

Another way to describe this is using Absolute Risk Reduction for all-cause mortality.  The ARR = 0.146%.  So, yes, runners did have a 30% lower risk of dying from any cause but the risk of dying was low anyway (0.45% in non-runners) so 30% isn’t really much of a difference.

The big problem with the conclusions stated by the researchers is that association does not equal causation.  They found that runners had lower all-cause mortality.  That does not prove that running reduces mortality.  In fact, in another part of the study, non-runners at the first visit who became runners as of a later visit, did not have lower mortality.  This study observed people who chose to run and chose how much they ran.  Higher duration, frequency, and/or intensity of running did not result in lower mortality.

Which leads to the newspaper headline.  Can running five minutes per day add three years to your life?  Probably not.  The study didn’t even attempt to answer that question.  They estimate that the life expectancy of non-runners  is three years shorter than runners.

This study is not proof that, if you start running, you will live longer.

Ban reporters from scientific meetings.

I’m serious.  Scientific meetings should be for scientists to disseminate results among themselves and plan future research.  Meeting coordinators need to stop holding press conferences and distributing press releases.  What is their goal?  Influencing funding?  All that seems to be accomplished is the proliferation of articles exaggerating or completely misinterpreting the results.  Studies presented at meetings are often pilot studies, preliminary analyses, and exploratory projects.  There’s no peer-review beyond selection of which studies are presented based on very brief abstracts (summaries).

An example:

AD retina

Your eye doctor could look at your eye and tell if you are developing Alzheimer’s Disease?!

No.

The studies described compared people with full-fledged Alzheimer’s Disease to people without the disease.  This is far from detecting it early.   In fact, based on the article, the test missed 15% of AD patients and misdiagnosed 5 – 15% of unaffected controls.

That’s another problem with reporters covering scientific meetings — we can’t read the actual source paper presenting the results because it doesn’t exist yet.  At a meeting, results are either presented as a short platform presentation with Powerpoint slides or as a large poster.  Sometimes results and conclusions change by the time the full paper is published which could be months to years later or even never.  In this case, I had to read four articles before one actually named the meeting:  Alzheimer’s Association International Conference in Copenhagen.

 

Math is hard.

When my children were young, math was patterns.  This persists quite far into elementary school with increasing complexity.  At least one CBC reporter is still having difficulty with putting things in order of increasing value.

In an article about a report ranking cities according to how expensive it is for an expat to live there, the author notes that “Vancouver was the 96th most expensive city in which to live, up from 64 in 2013”.

In what world is dropping from a ranking of 64 to 96 considered to be moving “up”?

What’s interesting is that nowhere does the report or the article give any information about how much is actually costs to live in Vancouver for a year.  The information is all relative.  Vancouver may be ranked lower because the cost of living there fell or because the costs in other cities increase.  Unless you are trying to decide which of the ranked cities you should move to, the ranking is rather useless.

There are too many reporters trying to fill up too much space with something.

This is the text of a Letter to the Editor that I’ve just submitted.

Heather Hanes is wrong about the research project being initiated at the University of Regina (SP, June 16, 2014 “U of R begins pesticide research study”). They don’t have a hypothesis. They have an agenda. Tanya Dahms admits that the goal is to eliminate pesticides. Her tone implies that they are simply going through the motions to gather evidence of what they already assume to be true. A real scientific inquiry would ask “How does pesticide use affect plant populations in a grass lawn?” It is possible that killing dandelions and other noxious weeds allows non-weed species to flourish. No one can know until the study is complete and even then they might have no useful answer since two test plots is a tiny trial and the researchers are obviously biased.

What are the risk factors for motor vehicle deaths?

A recent video that I’ve seen reposted a number of times shows moviegoers reacting to a PSA about cell phones and driving.  It ends with a message including the claim that “mobile use is now the leading cause of death behind the wheel.”  I don’t know if that’s true in Hong Kong but it didn’t sound true for Canada.

cell + automobile video screen grab

I found an excellent source of data from the BC Injury Research and Prevention Unit.  There’s no category for cell phone use but almost 30% of fatal collisions involved alcohol as a contributing factor and the same is true in Saskatchewan.  In fact, nationally almost 40% of drivers killed in accidents whose blood was tested had alcohol in their systems.

Percentage Of Fatally Injured Drivers Tested And Found To Have Been Drinking (BAC* >0 mg%) 1991–2010

alcohol and auto fatalities

As Kate at Small Dead Animals says, “when the call ends, the driver is sober.”  See her post for more evidence of the reduction in fatal accidents since cell phone use has expanded.

I still believe that no one should text while driving but banning all cell phone use is too much.