There are different approaches to non-invasive intracranial pressure measurement, which include ultrasound "time-of-flight" techniques, transcranial Doppler, methods based on acoustic properties of the cranial bones, EEG, MRI, tympanic membrane displacement, oto-acoustic emission, ophthalmodynamometry, ultrasound measurements of optic nerve sheath diameter, and Two-Depth Transorbital Doppler. Most of the approaches are "correlation based". Such approaches can not measure an absolute ICP value in mmHg or other pressure units because of the need for individual patient specific calibration. Calibration needs non-invasive "gold standard" ICP meter which does not exists.

Non-invasive absolute intracranial pressure value meter, based on ultrasonic Two-Depth Transorbital Doppler technology, has been shown to be accurate and precise in clinical settings and prospective clinical studies. Analysis of the 171 simultaneous paired recordings of non-invasive ICP and the "gold standard" invasive CSF pressure on 110 neurological patients and TBI patients showed good accuracy for the non-invasive method as indicated by the low mean systematic error (0.12 mmHg; confidence level (CL) = 0.98). The method also showed high precision as indicated by the low standard deviation (SD) of the random errors

(SD = 2.19 mmHg; CL = 0.98).

This measurement method and technique (the only non-invasive ICP measurement technique which already received EU CE Mark approval) eliminates the main limiting problem of all other non-successful "correlation based" approaches to non-invasive ICP absolute value measurement - the need of calibration to the individual patient.

The development of accurate and reliable non-invasive ICP measurement methods for VIIP has the potential to benefit many patients on earth who need screening and/or diagnostic ICP measurements, including those with hydrocephalus, intracranial hypertension, intracranial hypotension, and patients with cerebrospinal fluid shunts. Current ICP measurement techniques are invasive and require either a lumbar puncture, insertion of a temporary spinal catheter, insertion of a cranial ICP monitor, or insertion of a needle into a shunt reservoir.

There are relatively simple tests for radon gas. Radon test kits are commercially available. The short-term radon test kits used for screening purposes are inexpensive, in many cases free. Discounted test kits can be purchased online through The National Radon Program Services at Kansas State University or through state radon offices. Information about local radon zones and specific state contact information can be accessed through the EPA Map at https://www.epa.gov/radon/find-information-about-local-radon-zones-and-state-contact-information. The kit includes a collector that the user hangs in the lowest livable floor of the dwelling for 2 to 7 days. Charcoal canisters are another type of short-term radon test, and are designed to be used for 2 to 4 days. The user then sends the collector to a laboratory for analysis. Both devices are passive, meaning that they do not need power to function.

It should be noted that the accuracy of the residential radon test depends upon the lack of ventilation in the house when the sample is being obtained. Thus, the occupants will be instructed not to open windows, etc., for ventilation during the pendency of test, usually two days or more.

Long-term kits, taking collections for 3 months up to one year, are also available. An open-land test kit can test radon emissions from the land before construction begins. A Lucas cell is one type of long-term device. A Lucas cell is also an active device, or one that requires power to function. Active devices provide continuous monitoring, and some can report on the variation of radon and interference within the testing period. These tests usually require operation by trained testers and are often more expensive than passive testing. The National Radon Proficiency Program (NRPP) provides a list of radon measurement professionals.

Radon levels fluctuate naturally. An initial test might not be an accurate assessment of a home's average radon level. Transient weather can affect short term measurements. Therefore, a high result (over 4 pCi/L) justifies repeating the test before undertaking more expensive abatement projects. Measurements between 4 and 10 pCi/L warrant a long-term radon test. Measurements over 10 pCi/L warrant only another short-term test so that abatement measures are not unduly delayed. Purchasers of real estate are advised to delay or decline a purchase if the seller has not successfully abated radon to 4 pCi/L or less.

Since radon concentrations vary substantially from day to day, single grab-type measurements are generally not very useful, except as a means of identifying a potential problem area, and indicating a need for more sophisticated testing. The EPA recommends that an initial short-term test be performed in a closed building. An initial short-term test of 2 to 90 days allows residents to be informed quickly in case a home contains high levels of radon. Long-term tests provide a better estimate of the average annual radon level.

When exposure to a carcinogenic substance is suspected, the cause/effect relationship on any given case can never be ascertained. Lung cancer occurs spontaneously, and there is no difference between a "natural" cancer and another one caused by radon (or smoking). Furthermore, it takes years for a cancer to develop, so that determining the past exposure of a case is usually very approximative. The health effect of radon can only be demonstrated through theory and statistical observation.

The study design for epidemiological methods may be of three kinds:

- The best proofs come from observations of cohorts (predetermined populations with known exposures and exhaustive follow-up), such as those on miners, or on Hiroshima and Nagasaki survivors. Such studies are efficient, but very costly when the population needs to be a large one. Such studies can only be used when the effect is strong enough, hence, for high exposures.

- Alternate proofs are case-control studies (the environment factors of a "case" population is individually determined, and compared to that of a "control″ population, to see what the difference might have been, and which factors may be significant), like the ones that have been used to demonstrate the link between lung cancer and smoking. Such studies can identify key factors when the signal/noise ratio is strong enough, but are very sensitive to selection bias, and prone to the existence of confounding factors.

- Lastly, ecological studies may be used (where the global environment variables and their global effect on two different populations are compared). Such studies are "cheap and dirty": they can be easily conducted on very large populations (the whole USA, in Dr Cohen's study), but are prone to the existence of confounding factors, and exposed to the ecological fallacy problem.

Furthermore, theory and observation must confirm each other for a relationship to be accepted as fully proven. Even when a statistical link between factor and effect appears significant, it must be backed by a theoretical explanation; and a theory is not accepted as factual unless confirmed by observations.

Zhu Ling (, born 1973) is best known as the victim of an unsolved 1995 thallium poisoning case in Beijing, China. Her symptoms were posted to the Internet via a Usenet newsgroup by her friend from Peking University, Bei Zhicheng and were subsequently proven to be caused by thallium poisoning. Her case was then reviewed by physicians in many different countries who examined her symptoms and made suggestions as to diagnoses and treatment. This effort was recognized as the first large scale tele-medicine trial. Her life was ultimately saved, but she suffered serious neurological damage and permanent physical impairment.

This case drew great attention in the Chinese media, because the victim and the suspect were living in the same dormitory in the most prestigious university of China, and the case was never solved. Internet discussion of the crime has continued since then and became a hot topic on major online Chinese communities very frequently as a high-profile cold case.

In 1994, Zhu Ling was a sophomore in Class Wuhua2 (Class 2 majored in Physical Chemistry) at Tsinghua University in Beijing. Classmates described her as attractive, intelligent, and talented, with an interest in music. She began to show strange and debilitating symptoms at the end of 1994, when she reported experiencing acute stomach pain, along with extensive hair loss. Following her hospitalization at TongRen Hospital, her condition gradually improved and she was allowed to return to school. The following March, however, her old symptoms returned worse than before, this time accompanied by pain in her legs, loss of muscular eye control, and partial facial paralysis. Unable to breathe on her own, she was placed on a respirator.

One physician at Peking Union Medical College Hospital (PUMCH), Dr. Li Shun-wei, reported having diagnosed a similar poisoning case in the 1960s and strongly suspected that Zhu Ling's symptoms were caused by thallium poisoning. However, Zhu Ling denied that she had had any contact with thallium in class, a claim which was confirmed by her university's chemistry department. As a result, her doctors ruled out thallium poisoning as a potential cause. Instead, she was diagnosed with and treated for Guillain–Barré syndrome. Her condition deteriorated rapidly.