09-13.5 null chi P value

09-13.5 null chi P value - Null Hypothesis The null...

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Null Hypothesis The null hypothesis is that results obtained are a consequence of random chance Null Hypothesis Regardess of how much Zyfack™ is added, there will be no significant change in blood pressure. Note that even though there is variation, the average value shows no change. Experimenter’s hypothesis – As Zyfack™ is increased, blood pressure will significantly decrease. Note that even though there is variation, there is a definite downward trend in the average blood pressure. NOTE: in this example, we say there is a negative correlation between increasing Zyfack dosage and blood pressure. If we have successfully controlled (isolated) Zyfack as the dependent variable, we might conclude a causal relationship: Zyfack causes blood pressure to decrease
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P-values p is the probability that the result obtained could occur by random chance if the null hypothesis is true Although there could be valid arguments, scientists generally agree on the convention that one rejects the null hypothesis if p < 0.05 (i.e. less than 5% confidence that the null hypothesis is true). p-values are calculated in different ways depending on the context Linear regression, use t-values for data plotted with two points Chi-square p-values for categorical data (as in genetic problems)
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P-values and Sampling It is usually not convenient to measure the whole population (e.g. all coin tosses possible, all offspring ever obtained from mating of parents with certain genotypes, all voters in a district, etc.). Instead, inferences are usually based on a sample of the population. Sometimes there is an expectation, for example a nutritional supplement’s claim of effectiveness. In this case, the null hypothesis is that a sample will deviate from the expectation only randomly. What are some important considerations in sampling? random independent sample should be large enough to be representative and allow rare deviations to be averaged out
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P-values P-values are derived from the normal distribution and standard deviations The curve below depicts a p-value of 0.05, or the area of the curve within two standard deviations above/below the mean The null hypothesis correlates with the mean Any value found outside the two bars is beyond the range of normal deviation and probably did not occur by chance
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P-values p-values refer to the probability of an event occurring and do not imply certainty Selection of a P < 0.05 is arbitrary The smaller the p-value, the more likely the relationship is real p < 0.05 p > 0.05 Shows that An external influence caused a significant change There was an insignificant difference in the values Null Hypothesis Rejected Fail to reject (accept) Key Words • relationship did not occur by chance • There is a relationship • There is no relationship • Results occurred within normal deviation
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Example Left-handed people have a higher average IQ than right-handed people. You conduct an experiment
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This note was uploaded on 04/05/2012 for the course HLTH 311 taught by Professor Anderson during the Spring '12 term at BYU.

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09-13.5 null chi P value - Null Hypothesis The null...

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