Case control study

Case-Control Study; Perfluoroalkyl Substances and Its Relation to Childhood Autism
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Case-Control Study; Exposure to Perfluoroalkyl Substances and Its Relation to Childhood Autism
Article: Liew, Z., Ritz, B., von Ehrenstein, O. S., Bech, B. H., Nohr, E. A., Fei, C., & … Olsen, J. (2015). Research: Children’s Health. Attention Deficit/Hyperactivity Disorder and Childhood Autism in Association with Prenatal Exposure to Perfluoroalkyl Substances: A Nested Case–Control Study in the Danish National Birth Cohort. Environmental Health Perspectives, 123(4), 367-373. doi:10.1289/ehp.1408412
The above article is a case-control article which tries to investigate if exposure to perfluoroalkyl substances (PFASs) is associated with childhood autism or attention-deficit/hyperactivity disorder (ADHD) among children (Liew et al., 2015). The study was conducted by in the year 2015 by students from California and Aarhus University and in epidemiology department. A nested case-control study was used to determine the effect of PFASs exposure and ADHD. The students focused on Danish National Birth Cohort (DNBC) to examine more about PFASs and ADHD. DNBC helps to study pregnancies and various types of health-related outcomes that children will show after birth. When PFASs were measured during the mid-pregnancy, it showed that childhood autism is not associated with exposure to PFASs. Also, the results suggested that increase in the risk of ADHD is not associated with exposure to PFASs (Liew et al.

, 2015). The study reported PFASs relative risk or relative ratio (RR) of 0.98, 0.82, 0.87, and 0.92. In general, all the samples used, that is ADHD case group, autism, and the control group did not consistently provide evidence on how prenatal PFAs exposures result in childhood autism.
The study has external validity since the results were summarized after PFASs was studied on interaction with other environmental chemicals such as chlorine. From the survey, we can see that the more research was conducted in other schools in the USA to find out childhood autism and PFASs exposure. The four Bradford-Hill Criteria that I will consider are the strength of association, consistency, specificity, and plausibility. Strengthen criteria tend to look at the size of the risk and appropriate tests which are used to prove the firm association. The results gave approximately 95% confidence interval which showed that the research was correctly done. Consistency tries to explain the existence of causal if the association occurs repeatedly. The study was conducted for an extended period and more samples collected to help with further details about the investigation. The outcomes showed that children contact with PFASs does not affect their health and it does not lead to ADHD.
Part II
Relative risk can be defined as a measure of a risk occurring in one group compared to the risk that arises in another category or group. The formula is given by; risk in the treatment group divided by risk in the control group. Relative risk is different from odd ratio since in odd ratio we measure the relationship between an exposure and the outcome.
coffee drinkers (20,000) non-coffee drinkers (50,000)
developed anxiety 500  250
Did not developed anxiety 19,500 49,750

Relative risk= (500/20000) ÷ (250/50000)
RR= 0.025/0.005
RR=5
Fraction is 1/5
The absolute effect appears to be different for groups which show low and high risks, but the relative effect is always the same.
RR=0.75 mean it is less than 1. It means vitamin D supplement decreases the risk of prostate cancer.
The null hypothesis is; there is no relationship between vitamin D supplement and prostate cancer.
The P value= 0.20. The p-value is less than 0.5 which shows that there is strong support against the null hypothesis. Hence, we will reject the null hypothesis. The confident interval showed that 0.95% of the cohort would use vitamin D to assist in prostate cancer.
Controlled clinical trials it where participants are given one type of intervention so that research can be conducted. Community intervention it is whereby a chosen community is used to sample to study an outcome. In controlled experiments, one can be able to collect more data, but in the quasi-experiment, all groups have the same chance and cannot give more defined results.

Reference
Liew, Z., Ritz, B., von Ehrenstein, O. S., Bech, B. H., Nohr, E. A., Fei, C., & … Olsen, J. (2015). Research: Children’s Health. Attention Deficit/Hyperactivity Disorder and Childhood Autism in Association with Prenatal Exposure to Perfluoroalkyl Substances: A Nested Case–Control Study in the Danish National Birth Cohort. Environmental Health Perspectives, 123(4), 367-373. doi:10.1289/ehp.1408412