Identifying Causal Relationships

Validation of Methodology

A technique for identifying causal relationships involves calculating the correlation between two variables use various lagging parameters when pairing data cause and effect measurements.  The figure below is a demonstration of the validity of this technique that looks at the correlation between the number of minutes of cardiovascular activity and the calories burned by cardiovascular activity.  These two variables should be perfectly correlated, but neither is the cause of the other. As a result, we have a correlation coefficient near 1 when no lagging is performed. 

However, we also see a positive 0.25 correlation over a month of positive or negative lagging.  This correlation suggests that the subject is likely to have an above average time spent on cardiovascular activity during the previous month or coming month if they have above average calories burned by cardiovascular activity today.  This phenomenon is likely a product of human habit-forming behavior. 

In the below chart, we aggregate the predictor over various durations when generating the pairs to be used in the correlational analysis. 

You can see calories burned is most predicted the average time spend doing cardio on the previous day and least predicted by the average time spent over the previous 29 days. Again the positive correlation between the current cardio and cardio over the previous 29 days can also be attributed to habit. 

Effect Onset Delays

Now let’s consider a more useful question.  Does the nutritional supplement 5-HTP improve mood as is claimed?  

This chart shows that intake of 5-HTP predicts that the individual likely had a below average mood 30 days prior to consumption.  This makes sense because one is only likely to be motivated to take a supplement such as this if they are trying to alleviate depression.  We can see that mood generally improves over the 2 weeks following consumption.  This is consistent with anecdotal reports such as:

“I noticed a difference within 3 days. The negative self-talk and impulsiveness moved to the background then disappeared in a few weeks.” at https://www.webmd.com/vitamins-supplements/ingredientreviewpost-794-5-HTP

The first large clinical trial using 5- HTP in depression was conducted by Sano in 1972. Using an open trial design, a total of 107 patients with endogenous unipolar or bipolar depression were given daily oral dosages of 5-HTP from 50 to 300 mg. Significant improvement was observed in 74 of the patients (69%), and no significant side effects were reported. The response rate in most of these patients was quite rapid (less than two weeks).11

The issue of speed of response was subsequently addressed in a study of 59 patients with eight different types of depression. 5-HTP was administered orally in dosages from 150 to 300 mg daily for a period of three weeks. Thirteen patients (22%) were markedly improved, and another 27 patients (45.8%) showed moderate improvement. Of these 40 patients who improved, 20 (50%) began to show improvement within three days, and 32 patients (80%) improved within two weeks of beginning treatment with 5-HTP.15 In contrast to many conventional antidepressants which may take 4 weeks or longer to achieve therapeutic response in most patients, those taking 5-HTP appear to have a significantly more rapid response.

Mechanisms of Action 

5-HTP acts primarily by increasing levels of serotonin within the central nervous system. Other neurotransmitters and CNS chemicals, such as melatonin, dopamine, norepinephrine, and beta-endorphin have also been shown to increase following oral administration of 5-HTP.7-10 This ability to increase not only serotonin levels in the brain but also dopamine and norepinephrine, allows 5-HTP to produce some significant and unique effects on brain chemistry and on serotonin-related conditions which other substances, including L-Tryptophan, cannot duplicate.

Cumulative Duration of Action

One can also vary the window over which predictor measurements are aggregated when combining them with outcome measurements to identify cumulative impacts over time.  Psoriasis is a slow-moving autoimmune disease that causes plaque-like sores on the skin.

In the case of psoriasis severity, we can see that exercise in a single day has very little effect.  However, the amount of exercise over the previous 30 days may lead to significant improvement in the condition. 

As anyone who has suffered from this disease knows, changing direction in this skin disorder is more akin to changing course on a huge ocean liner compared to the rapid speed at which mood-related symptoms can fluctuate.

The suggestion from the QuantiModo analysis is consistent with most published research indicating that cardiovascular activity can exert a positive effect on psoriasis.

Probiotics and Mood

Probiotic intake was observed to pos

Correlation vs Causation

How can we tell if one symptom is likely the cause of another or merely a correlation possibly resulting from a third underlying cause?  Here we examine the relationship between self-reported energy levels and acne severity.  You can see that the strongest negative correlation is seen with a 0-day offset.  This means that days with above average acne severity tend to coincide with days with below average energy.  The likely underlying mechanism relates to elevated cytokine levels in the bloodstream which can trigger an inflammatory acne response as well as interfere with the conversion of tryptophan to melatonin, decreasing sleep quality. 

Additionally, we see that there’s a positive correlation between an individual’s mood and the number of things they like on Facebook.  It’s almost definitional that there’s a correlation between mood and liking stuff.  The hypothesis that this is merely a correlation rather than a causal relationship is consistent with the following chart which shows no difference between positive and negative lagging of the data prior to correlational analysis.

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