Sample statistics papers
Statistics 101: Estimating Sample Size Requirements
Statistics 101: Estimating Sample Size Requirements.
When constructing confidence intervals we usually choose the sample size, alpha level, and are given/assume a population standard deviation. In this video we learn what sample size would be required if we want a level of confidence given a margin of error of our choosing. So we rearrange the terms that comprise the margin of error to achieve this. This video contains 4 brief example problems so you can see applications and the relationships between all of the parts of the margin of error. Enjoy!
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Комментарии:
Brandon Foltz пишет: Confidence intervals for variances are much more involved and that is actually the next topic I will cover. You do not need to know how to find those to do any of the problems up to this video in the playlists. :) ybeholla45 пишет: A problem I am working on mentions. The types of widgets used typically fall into the second classification on the company's pricing scale. This classification places an upper limit of 850 pounds on the mean. There is no mention of a lower limit. In determining E am I to assume 2 classifications above the mean and 2 below for a total of 4? Or am I to work with the upper limit value? Wei Chen пишет: It help a lot Desiree del Rosario пишет: sir,,i came across with your videos,,i am looking for a sampling method applicable in my study..my study is about the use of ATM Card in our school.. the problem is not all students have an ATM..how can I get a sample size knowing that i don't know how many students are using an atm?..the only thing I know is the population of the student body..help me pls.thanks sir Brandon Foltz пишет: Hello! First and foremost there is no "easy button" for this. It will take hours of doing practice problems in your book and/or notes; preferably in a study group if that is possible. Secondly, I have not covered a few of those topics...yet. The goal of my videos has been for people like yourself to recognize the basic pattern and method for working these and then apply them in your classwork. Practice, study groups, note cards, reviewing examples in your book. Just a few ideas. You can do it! Firdhous Fir пишет: wow! this is the very similar question out in ASQ CQE exam practice paper and I was always wondering why only a portion of the equation used to get the sample size, n. Many thx for this vid! Brandon Foltz пишет: Hallo. When finding confidence intervals we are usually given the sample size and that determines that margin of error. In this case we are reversing it. We are given a margin of error and then we are solving for the sample size that will produce the margin of error we chose at the beginning. For example a rectangle, we know that Area = L x W. If we know 2 of these, we can solve for the other. Same thing here. We are just solving for a different unknown. SouthpawGrammar пишет: I'm trying to solve this problem, and just couldn't get the right answer. The Bureau of Alcohol, Tobacco, and Firearms (BATF) has been concerned about lead levels in California wines. In a previous testing of wine specimens, lead levels ranging from 53 to 680 parts per billion were recorded. How many wine specimens should be tested if the BATF wishes to estimate the true mean lead level for California wines to within 10 parts per billion with 95% confidence? Thanks lawalx пишет: Really educative videos. thanks a lot Antoinette Nelson пишет: I don't really comment on youtube much but I just watched two of your videos and they were extreeemeellyy helpful! I'm a PhD student and I needed to refresh myself on some statistics quickly for experimental design. Thanks a lot! Zoraida Obregon пишет: Brandon I desperately need your advice. I am being tested this coming Saturday for Confidence Intervals sigma known, sigma unknown, sample size, confidence intervals for proportions and finding confidence interval for a variance and standard deviation. What do you suggest I do in terms of studying for these with your videos? Thank you. RicksterBerlin пишет: If only I'd seen this before I took my Open University Data Analysis exam! The interpretation and case-study format of these videos brings the subject to life. That's what makes it stick. Highly recommended if you want bite sized nuggets of Stats know-how. Rickster Zoraida Obregon пишет: Brandon. Little confused with this video. Do you have a video for confidence intervals for variances and standard deviations. KPAVideoful пишет: Brandon, again great job! This video answer most of the question I have with regard to how to select the sample size with 95% ci and specified MoE. You explanation is really more of self explanation, which is a great way for this kind of distance/online leaning. It's Really really really helpful. I can't stop sharing your video with my friends. Thank you so much Brandon. Wei Chen пишет: Thanks ybeholla45 пишет: I have just started to listen to your videos for the first time and already, I am sold. First off, your intonation is nowhere near as monotonous and lifeless as my stat professors. You do a good job of briefly reviewing topics which are at the base of the new topics you mention. Thank you for your videos. I do have a question though. I will put the question in another post. Bereket Y пишет: Thanks Brandon It's really helpful. I just want to ask you if there are ranges of accepted margin of error that scholars use frequently. Thanks a lot! Brandon Foltz пишет: Confidence intervals for variances are much more involved and that is actually the next topic I will cover. You do not need to know how to find those to do any of the problems up to this video in the playlists. :) ybeholla45 пишет: A problem I am working on mentions. The types of widgets used typically fall into the second classification on the company's pricing scale. This classification places an upper limit of 850 pounds on the mean. There is no mention of a lower limit. In determining E am I to assume 2 classifications above the mean and 2 below for a total of 4? Or am I to work with the upper limit value? Wei Chen пишет: It help a lot Desiree del Rosario пишет: sir,,i came across with your videos,,i am looking for a sampling method applicable in my study..my study is about the use of ATM Card in our school.. the problem is not all students have an ATM..how can I get a sample size knowing that i don't know how many students are using an atm?..the only thing I know is the population of the student body..help me pls.thanks sir Brandon Foltz пишет: Hello! First and foremost there is no "easy button" for this. It will take hours of doing practice problems in your book and/or notes; preferably in a study group if that is possible. Secondly, I have not covered a few of those topics...yet. The goal of my videos has been for people like yourself to recognize the basic pattern and method for working these and then apply them in your classwork. Practice, study groups, note cards, reviewing examples in your book. Just a few ideas. You can do it! Firdhous Fir пишет: wow! this is the very similar question out in ASQ CQE exam practice paper and I was always wondering why only a portion of the equation used to get the sample size, n. Many thx for this vid! Brandon Foltz пишет: Hallo. When finding confidence intervals we are usually given the sample size and that determines that margin of error. In this case we are reversing it. We are given a margin of error and then we are solving for the sample size that will produce the margin of error we chose at the beginning. For example a rectangle, we know that Area = L x W. If we know 2 of these, we can solve for the other. Same thing here. We are just solving for a different unknown. SouthpawGrammar пишет: I'm trying to solve this problem, and just couldn't get the right answer. The Bureau of Alcohol, Tobacco, and Firearms (BATF) has been concerned about lead levels in California wines. In a previous testing of wine specimens, lead levels ranging from 53 to 680 parts per billion were recorded. How many wine specimens should be tested if the BATF wishes to estimate the true mean lead level for California wines to within 10 parts per billion with 95% confidence? Thanks lawalx пишет: Really educative videos. thanks a lot Antoinette Nelson пишет: I don't really comment on youtube much but I just watched two of your videos and they were extreeemeellyy helpful! I'm a PhD student and I needed to refresh myself on some statistics quickly for experimental design. Thanks a lot! Zoraida Obregon пишет: Brandon I desperately need your advice. I am being tested this coming Saturday for Confidence Intervals sigma known, sigma unknown, sample size, confidence intervals for proportions and finding confidence interval for a variance and standard deviation. What do you suggest I do in terms of studying for these with your videos? Thank you. RicksterBerlin пишет: If only I'd seen this before I took my Open University Data Analysis exam! The interpretation and case-study format of these videos brings the subject to life. That's what makes it stick. Highly recommended if you want bite sized nuggets of Stats know-how. Rickster Zoraida Obregon пишет: Brandon. Little confused with this video. Do you have a video for confidence intervals for variances and standard deviations. KPAVideoful пишет: Brandon, again great job! This video answer most of the question I have with regard to how to select the sample size with 95% ci and specified MoE. You explanation is really more of self explanation, which is a great way for this kind of distance/online leaning. It's Really really really helpful. I can't stop sharing your video with my friends. Thank you so much Brandon. Wei Chen пишет: Thanks ybeholla45 пишет: I have just started to listen to your videos for the first time and already, I am sold. First off, your intonation is nowhere near as monotonous and lifeless as my stat professors. You do a good job of briefly reviewing topics which are at the base of the new topics you mention. Thank you for your videos. I do have a question though. I will put the question in another post. Bereket Y пишет: Thanks Brandon It's really helpful. I just want to ask you if there are ranges of accepted margin of error that scholars use frequently. Thanks a lot!
Overview
The results of your statistical analyses help you to understand the outcome of your study, e.g. whether or not some variable has an effect, whether variables are related, whether differences among groups of observations are the same or different, etc. Statistics are tools of science, not an end unto themselves. Statistics should be used to substantiate your findings and help you to say objectively when you have significant results. Therefore, when reporting the statistical outcomes relevant to your study, subordinate them to the actual biological results.
Reporting Descriptive (Summary) Statistics
Means . Always report the mean (average value) along with a measure of variablility ( standard deviation(s) or standard error of the mean ). Two common ways to express the mean and variability are shown below:
"Total length of brown trout (n=128) averaged 34.4 cm ( s = 12.4 cm) in May, 1994, samples from Sebago Lake."
s = standard deviation (this format is preferred by Huth and others (1994 )
"Total length of brown trout (n=128) averaged 34.4 ± 12.4 cm in May, 1994, samples from Sebago Lake."
This style necessitates specifically saying in the Methods what measure of variability is reported with the mean.
If the summary statistics are presented in graphical form (a Figure), you can simply report the result in the text without verbalizing the summary values:
"Mean total length of brown trout in Sebago Lake increased by 3.8 cm between May and September, 1994 (Fig. 5)."
Frequencies: Frequency data should be summarized in the text with appropriate measures such as percents, proportions, or ratios.
"During the fall turnover period, an estimated 47% of brown trout and 24% of brook trout were concentrated in the deepest parts of the lake (Table 3)."
Reporting Results of Inferential (Hypothesis) Tests
In this example, the key result is shown in blue and the statistical result . which substantiates the finding, is in red.
"Mean total length of brown trout in Sebago Lake increased significantly (3.8 cm) between May (34.4 ± 12.4 cm, n=128) and September (38.2 ± 11.7 cm, n = 114) 1994 (twosample t-test, p < 0.001) ."
NOTE: AVOID writing whole sentences which simply say what test you used to analyze a result followed by another giving the result. This wastes precious words ( economy . ) and unnecessarily increases your paper's length.
Summarizing Statistical Test Outcomes in Figures
If the results shown in a figure have been tested with an inferential test, it is appropriate to summarize the outcome of the test in the graph so that your reader can quickly grasp the significance of the findings. It is imperative that you include information in your Materials and Methods, or in the figure legend, to explain how to interpret whatever system of coding you use.
Several common methods for summarizing statistical outcomes are shown below.
Examples: Comparing groups (t-tests, ANOVA, etc)
Comparison of the means of 2 or more groups is usually depicted in a bar graph of the means and associated error bars.
For two groups . the larger mean may have 1-4 asterisks centered over the error bar to indicate the relative level of the p-value. In general, "*" means p< 0.05, "**" means p< 0.01, "***" means p< 0.001, and "****" means p<0.0001. In all cases, the p-value should be reported as well in the figure legend
The asterisk may also be used with tabular results as shown below. Note how the author has used a footnote to define the p-values that correspond to the number of asterisks. ( Courtesy of Shelley Ball )
For three or more groups there are two systems typically used: lines or letters. The system you use depends on how complicated it is to summarize the result. The first example below shows a comparison of three means. The line spanning two adjacent bars indicates that they are not significantly different (based on a multiple comparisons test), and because the line does not include the pH 2 mean, it indicates that the pH 2 mean is significantly different from both the pH 5.3 (control) and the pH 3.5 group means. Note that information about how to interpret the coding system (line or letters) is included in the figure legend.
20_stats.jpg" /%
When lines cannot easily be drawn to summarize the result, the most common alternative is to use capital letters placed over the error bars. Letters shared in common between or among the groups would indicate no significant difference.
Example: Summarizing Correlation and Regression Analyses
For relationship data (X,Y plots) on which a correlation or regression analysis has been performed, it is customary to report the salient test statistics (e.g. r, r-square) and a p-value in the body of the graph in relatively small font so as to be unobtrusive. If a regression is done, the best-fit line should be plotted and the equation of the line also provided in the body of the graph.
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