formula for calculating sample size of population

Hi, I’m student from Lithuania. You can calculate this using our sample size calculator. You should clearly report these numbers in your report. However, a population size is fixed. I have a project in school and in my project i am doing a survey to all the students who use Facebook. gender, prior education, etc.) btw, my confidence level is 95%, and margin of error 5%. Your sample size for a survey is based on the question with the greatest variability in the sampled population. When you dispose of email addresses of the customers, you can perfectly send out an online survey to a large group and collect responses within a couple of weeks. View our sample size formulas for our sample size calculator from Creative Research Systems. For example, for a population of 10,000 your sample size will be 370 for confidence level 95% and margin of erro 5%. After calculation of sample size you have to correct for the total population SSadjusted = (SS) / (1 + [(SS – 1) / population]). (Z-score)² – StdDev*(1-StdDev) / (margin of error)². SSadjusted = (SS) / 1 + [(SS – 1) / population] SSadjusted = 384.16 / 1 + ((384.16 – 1) / 353,534) SSadjusted = 384.16 / 1.001084 SSadjusted = 383.74 => 384, Hello! I would make a pro rata split in this case, e.g. You can calculate for yourself with our sample size calculator. However, instantly a new question comes to the forefront: “How many people should my sample consist of?”. If there are clear differences between weeks, then you should use multiple weeks to calculate your sample. For a social science project, would a CI of 8 % and a CL of 90% seem appropriate? That is, say you have a particular population size and it has some mean which is a data point. Where n is the sample size, N is the population size, and e is the level of precision. Your sample is too small to make reliable conclusions for your population. Based on this limited information, it is rather difficult for me to answer your questions. I did utilize the sample calculator, which is essentially telling me that I will need to include close to the entire population for a 5% margin of error w/ 95% confidence. I am not entirely familiar with this kind of analysis, but I would first try to create several respondent profiles out of the survey using structural equation modelling and second using multinomial logistic regression to link the 4 million people to a corresponding profile. Let’s say that you have an average of 30 patients per day, then your monthly population will be 900. This will also be translated in the results for the entire population. After calculation of sample size you have to correct for the total population SSadjusted = (SS) / (1 + [(SS – 1) / population]) In your case: SS = (1,96²) * 0,5*0,5 / 0,0438² = 500,6 SSadj. Thank you very much for your reply and advises. However, you do need to know whether your sample was drawn from a population larger than 1.000.000 or not. Using the table from the article, this would mean that you need at least 400 respondents. However, I take it from the table above that a response of 1% (73*6=43873) completed surveys for a population of 43, 800 (73*600) is sufficient to give a true reflection on customer satisfaction with the company itself? i don’t know the population of informal traders from these sites. To find out whether your survey sample is representative for the population you should compare the distribution of these characteristics between your survey sample and the population. I do not want to go for a bigger sample . my population is unknown then how can i check my sample size. Formula that is used to calculate sample size. Thnx for your time and congratulations for your work! This means if for instance 60% of your sample selects a certain answer option, the actual percentage for your population will be between 44% (60-16) and 76% (60+16). Hello Sir, for a population of 500 how many sample do I need to take? You can lower your confidence level to 90%, but then your results will be less reliable. Also I would like to know if I could focus in only one specialised department (for example ophthalmology) with different work positions such as for example administratives, nurses, specialised professionals. X = Z α/22 ­*p* (1-p) / MOE 2, and Z α/2 is the critical value of the Normal distribution at α/2 (e.g. Hi Sir, What is may sample size if i have 322 population? Sample sizes for small populations are conducted the same way large populations are conducted. If you want your survey data to reflect very closely the entire population, then you should choose a high confidence level (99%) and a low margin of error (1%). It is really appreciated. See below: n= N/ (1+N (e) 2) Where: n signifies the sample size. The population that corresponds with a sample size of 117 depends on the confidence level and margin of error. Because for what I have search is a non-probabilistc since not all the population studied have the chance to be select (university students will be a sub-group of the universe (French people). Hi Didier I am conducting a survey questionnaire study comparing 2 groups.. Presumably, this will only be Ghanaians that have a car or driver’s licence. as i seen fro the above explanaion. I am planning to do a survey with a total population of 132 workers. and 3. how much from each area of study ( natural sciences group, bio sciences group, social sciences group) ?? is it possible to distribute your questionnaire in a single institution which can cover your sample size and collect your data. From 1880 I took 94 households, and from 578 I took 56- here I doubled the percent because I thought the number was too small for comparison between the two villages. . For large populations the sample size does not change a lot (e.g. Thank you Adebayo. But unfortunately, It turned out that I was able to get only 183 respondents. The population is 475. to measure my study population for cross- sectional survey? However, you can easily compare the proportions of each category using e.g. To calculate your overall response rate, you should divide your total number of responses by the sum of the number of invitations of survey A and B. dear Didier, thanks a lot for your amazing information, it helped a lot to clear a lot of issues that I have with near to submit research :) a quick question, according to CL of 95% and ME of 5% I get 384 population sample for a population of 1200000. To make your project manageable, it is perhaps wisely to limit yourself to those Ghanaians that have been in contact with this authority in the past year. The z-score depends on the confidence interval you chose. Based on your pilot study you can estimate s > s=s’*(n’/(n’-1))^0,5 with n’= sample size of your pilot study, and s’= standard deviation of sample of the pilot study. For such specific information I suggest you post your question on a statistics forum, for instance the LinkedIn Group Research, Methodology, and Statistics in the Social Sciences, Hi, Can these tables be used after the fact, to infer margin of error and confidence level after a survey has been administered to an entire population. 1. However, before you launch the new line you wish to conduct an online survey on whether your line ‘Fall – 2016’ is more or less likely to be a hit or miss on the European Union (EU) market. An example: Consider a population of 10.000. good day! Here is an example that came up earlier in this post that gives detailed info on the formula: First you calculate the sample size (SS). Sample size calculation is important to understand the concept of the appropriate sample size because it is used for the validity of research findings. Generally a confidence level of 95% and margin of error of 5% is taken. IS this right? Should you survey 1%, 5%, 10%, … of the adult citizens in the EU? Thank you for your interesting questions. Could I do less than 100 or would I need to find more? here i am planning to study an effectiveness of an exstension tool to diisiminate a techenology adoption .in the study districts there are 22 districts among them i select purposely district A since the district is adopting a techinology(precence of techinology). You can check for other error margins/confidence levels with our sample size calculator. The formula to calculate sample sizes is: SS = (Z-score)² * p*(1-p) / (margin of error)². Z-score = 1,96 for confidence level 95% Proportion p is your expected outcome. Are there authorities who for example talk of 50%, 20%, Your sample size depends on the margin of error (2% 5% 10%?) What sample size is needed to estimate the population total, \(\tau\), to within d = 1000 with a 95% CI? I want to study Determinants of Seasonal Migration in one woreda of Ethiopia with sampled kebele of three with house hold of 2473,so what type of Formula i can used in 95% accuracy and 5% errors and the sampled use hold be ranged between 120-180. Only 51 completed. how many states would be enough? Village A 1022 population, village B 603, and Village C 383. So, the optimum would be that z% would be much higher than w%. The minimum sample number depends of the margin of error you want to accept. Please comment. Dear Gert, I understand you do market research but maybe you could help over this (same principle). The total number of students is not known. My population is MUCH smaller (roughly 550 students) than those mentioned above and once the proposal is submitted and approved I will have only 5 to 6 weeks to gather representative data. the 100.000 students of 7 universities), you need roughly 2.345 respondents (margin of error 2% and confidence level 95%). Can I just get the 10% or 20% of the population to be my respondents? This is because I was expected to collect minimum of 240 in order to conclude the research. As you point out, a minimum sample of 30 is recommended. For this we use the second measure: the confidence level. ~~~~~ This channel does not contain ads. In other words, how closely you want your results to match those of the entire population. and am using survival model and i have 4000 populations so, how i can calculat sample size???? To find out whether your survey sample is representative for the population you should compare the distribution of some demographic characteristics between your survey sample and the population. REGARDS, You need a sample size of 245 for this population, confidence level 95,45% and margin of error 2% Formula: first you calculate the sample size(SS). You can check the margin of error using our calculator: https://www.checkmarket.com/market-research-resources/sample-size-calculator/. Thank you. :) The formula is by Cochran and this is the calculation: The first step is to calculate the sample size for infinite populations. 2. identify dependent and independent variables to be used in this study. I think this differs a bit from your proposed calculations. Thank you very much. But if I considered the population as a whole I would give 384, which would give me about 40 per age group. So you can either try to get these extra 100+ factories to participate in your research or at least clearly mention the margin of error is higher than accepted in your report so that readers know how to interpret your results. ex. If you don’t have any idea about the proportion, you can take 0,5. Can someone just say like that without calculating. So, I have population of 353,534 and its says in the sample size calculator that the required sample size is 384 with a margin of error of 5% and a confidence level of 95%. question is how I can get.a representative sample. To find out the employee contribution to SOCSO towards their productivity at workplace. how to determine a sample size from a population size of 7914. I don’t know what should I do because I really suffered just to get this response rate! We’re here to help! Having said that, as I explained in previous comments you do not necessarily need the population size to calculate the sample size. If that is not possible, it is also an option to reweigh your results afterwards in a statistical software pack (e.g. Based on these you should start calculating your sample and make sure that the distribution in your sample roughly equals the distribution in the population. If you do not know your proportion p, it is quite common to take 0,5 as a value for p. SS = (Z-score)² * p*(1-p) / (margin of error)² Then you correct it if you know your population: SSadjusted = (SS) / 1 + [(SS – 1) / population] If we use it in an example with a population of 100.000, confidence level of 95% and margin of error 2%, then you get the following calculation: SS = (1,96²) * 0,5*0,5 / 0,02² SS = 3,8416 * 0,25 / 0,0004 SS = 0,9604 / 0,0004 SS = 2401 SSadj. User our calculator for this: https://www.checkmarket.com/market-research-resources/sample-size-calculator/. Thanks, but if total population is 596411 what percentage should I take and what is the sample? I have managed, over 2 weeks, to collect only about 100. The population is cca 3000 and my sample size is cca 120. If so, how is this done? Am conducting a study in a small organisation with not more than 37 staff and I thought I would consider the population as my sample size. How di I get a representative sample if my target population includes all current households, Thanks a lot,but I dnt need a formular. How will I calculated sample size? Your results will only make sense for the 10 banks you have investigated and you cannot extrapolate this to the total banking industry (unless these 10 banks represent almost the total banking industry in the region you are investigating) . The only way to lower your margin of error is increasing your number of respondents. as you’ve correctly calculated, you will need a sample of 172 respondents for this survey (error 5%, CL 95%). for example , if i have 15 wards and i intend choosing 30%,or 10% etc of that wards. I am afraid both approaches are ‘wrong’. I do not have the resources for a large sample size. You can do this by using our calculator: https://www.checkmarket.com/market-research-resources/sample-size-calculator/. For example your can include only people younger than 25 in your sample of 400. HI THERE I HAVE A QUESTION ; CRITICS OF PROBABILITY SAMPLING OBJECT THAT HOW CAN 300 OR 400 RESPONDANTS REPRESENT THE VIEWS /OPINION/ ATTITUDES OF A POPULATION AS BIG AS THE WHOLE CITY OR ANY OTHER BIG GEOGRAPHIC AREA POPULATED BY A HUGE NUMBER OF PEOPLE .WHAT DO U THINK ABOUT THIS CRITICISM, I surely understand this criticism and In case of doing a respresentative study of a city, a researcher needs to critically reflect on which segmentationparameters matter eg education, gender and/or age. I am struggling a bit with: 1)sample size (as I am not sure which size of the population should I choose (is it the average number of patients admitted to this department by day, or by week ,or by month?? Will it be possible to achieve the target amount of respondents within the period of time. E.g. if not how would i use this data meaningfully? I want to study 150 people of a population of 1500 farmers. I was thinking 30% of the total population which is 360 and that seems really high given that its not an online survey, and respondents are students. Thanks in advance. More explanation and further information about determining sample size for estimating the mean can be found in this article. I shall be grateful with your answers to my three questions to save me from the confusing state. Hi I’m Yeshey, I have population 277 and what will be my sample size? Perhaps someone can chip in with a suggestion? When using a margin of error of 1% you need 906 respondents. If you want to draw conclusions separately per hospital, I would go for a mninmum of 50 per hospital. With your data it looks like this: 10! E.g. then it will not be enough. because my research in emergency department. Do you not have an idea about the total nr. Thanks, Well, you should first start by determining your actual margin of error. For instance, if you send out your survey to 400 people and you receive 200 filled in surveys, your response rate is 50%. Thanks for your follow-up question. You should definitely report these numbers as they will allow the reader of your study to interpret the results. Thanks for your continuous support you provide to online people. Indeed, your survey sample represents the members of the population you are working with. Once your population gets large, your sample size doesn’t change much anymore. if im properly guided on how to get the population, i can determine the sample from your explanation so far. Thank you so much in advance and best regards. For a margin of error of 5% at 95% confidence level, you will need a sample of 80 respondents. Which gives 5.78% margin of error ( Confidence level: 95%). For your total population the margin of error will be 2.5%. Hi, i am trying to conduct a clinical study to confirm the performance of a medical device we have. If, however they know from previous studies that they would expect a conversion rate of 5%, then a sample size of 73 would be sufficient. With an average staff of 150 per company, your total population will be around 5000. The reasoning is even the other way round. Hi! I would like to know how many students am I going to give a survey questionnaire in each classroom. SS = (Z-score)² * p*(1-p) / (margin of error)² Z-score = 1,96 for confidence level 95% When the proportion p is not known, it is common to use 0,5. It depends. of females in your population. Hello! You can use our sample size calculator to estimate your required sample size. Please help me to derive the formula and explaination of selecting the mimimum sample size from the population of 5,000 people. Hi, I am currently carrying out a statistical survey to determine if females perform better than males in STEM subjects. Commentsir i was given only population of 286. how can i calculate the appropriate sample size? e.g. How I can calculate my study sample, please? With 95% level of confidence and 10 % margin of errors. If you want to draw separate conclusions for these 2 groups (urban and rural) you can indeed consider this as 2 populations. Hi, nice post. will 1% sample size be accurate or 2% be good. Thank you very much! An airline estimates that approximately 70% of the members of its frequent flyer program desire access to on-board meals. Hi, I am researching birth characteristics in 300 mother/daughter pairs. I used 15% for each population to be my sample size. would tell me how i can calculate sample size for survival model and survival data if my population is curently 2128. please write down the formula and the given value such as HR,p,,,,, thanks for your coooperation. E.g. If the proportion is different from the 0.5, your margin of error will be less for the same sample size. a manufacturer would like to survey users to determine the demand potential for its new washing machine. Accuracy is determined by the following three variables: 1. please how do i calculate the sample size for an undefined population? Thank you. so in this particular case I would try to spread your sample over your different geographical regions. How can I defend the statement that a respins rate of 67% is good and sufficient? If your total population is 410, a sample size of 65 corresponds with a margin of error of 11% for a 95% confidence level. There are so many ways to determine sample size. You can distribute your survey in many different ways. To answer your question, no, that is not automatically the case. As explained in the article, your sample size not only depends on your population but also on the margin of error and the confidence level you choose. Yes, you should use the proportion of your own country. The only information I have to go on is an effect size of 0.20 and a power of 0.80. 14 respondents won’t be enough to extrapolate your results unless this is your entire population you are examining. I am sorry I am not able to help you better. for a population of 10,000, confidence level 95% and margin of error 5%, your required sample size is 370. As far as I am aware the idea behind consecutive sampling is to include all accessible subjects as part of the sample. In that way you would only need 3 * 384 = 1152 respondents. calculate sample sizes. Hi Gert, thank you for your support, but who is the author of the formula listed here? What formula should I use? ... My sample size is 384 using sample size calculator but the population from two geographic locations are Kachia – 120,893 and Dwudu – 432285. hence I … Often a 95% confidence level and margin of error of 5% is taken. hello, I need a guidance relating to sample size. I use all entire population in the study period ,still I am confused please Help me Thank you Africa, Ethiopia. The sample size for this population is 176. In other words, the number of patients per year. So I can better understand. Therefore, the sample size for N = 120,000 can be calculated as, = (120000 * (1.96 2)*0.05*(1-0.05)/(0.05 2)/(120000 – 1+((1.96 2)* 0.05*(1-0.05)/(0.05 2)))). In this case, my population will be all international passengers worldwide or only the number of international passengers for that particular airline on that particular rout. Hi all wondering if you could help. If you have a 280 population and you wanted to get a 20% sample size of this population, can that be justifiable and will there be any restrictions? After all, you could – for example – survey 100.000 citizens in each city but if your respondents primarily contain the ’35-54 higher-educated’ citizens, you can hardly speak of a representative sample. Hi, I have no idea about population, how can I find my appropriate sample size. Thank you in advance for kind consideration. how many should i draw from each group? This would mean that if you interrogate the total population, you can be sure that between 28,68% and 51,32% would pick the same answer. Or below you find the formulas for calculating your sample size for an known population: R/Sir, In a study stratified random sampling was used for the selection of the sample. E.g. Let’s say you want to investigate job satisfaction of high school teachers in a certain region. Assuming that you know the distribution of some parameters in your population, my advice would be to try to get as close as possible to representativeness. I am doing quantitative study in education population is 7000 how i calculate the sample size , is 200 sample size sufficient ? I have a population of 23,245 from the tables am required to use a sample size of 370, but I want to use 200 as my sample, can you justify a sample of 200 statistically. How the sample size calculator works The calculator helps you determine the number of people you need to survey (your sample size calculation) based the level of accuracy you want to achieve. Often confidence level 95% is taken and MoE 5%. Based on your pilot study you can estimate s > s=s’*(n’/(n’-1))^0,5 with n’= sample size of your pilot study, and s’= standard deviation of sample of the pilot study. Based on a population of 800 customers, a 5% confidence interval and a 95% confidence level, you would need a 260 a 300 respondents. Sir , my query is that how this sample size is calculated by using the above formula. how scientifically you can choose sample size based on non-probability technique? How do I discuss the confidence level (and how do I determine what a proper confidence level is?) Helpful discussion , I was enlightened by the information ! So what sampling technique may I employ. Hi, doesn’t number of questions on survey (degrees of freedom) also help determine the requisite sample size given confidence interval and confidence level. It is correct that your sample has to be 370 for a population of 10,000 and confidence level 95% + margin of error 5%. Sample size determination is the act of choosing the number of observations or replicates to include in a statistical sample.The sample size is an important feature of any empirical study in which the goal is to make inferences about a population from a sample. E.g. If you don’t have any idea about the proportion, you can take 0,5. A 95% confidence level and P = .5 are assumed for Equation 5. dear sir i want to take 90% confidence level , then what will be my sample size ? Using the table from the article, this would mean that you need at least 16.000 respondents. Hi, I am planning to apply for a grant application to analyse the role of psychosocial factors on wellbeing. I know about calculator software but i want to calculate it manually . Whay not 6 or 8 for example? I’m doing co relational study design in my research paper Convenience sapling My population is unknown How can I determine my sample size around 60 or 70 people not more than. However, if you want to segment between different socio-demographic groups (e.g. the population in one site is 4024, the other one is 3960. How can I determine a power level for a survey size of 150 with an 8% margin of error and 95% confidence level. Just to know are the sample size calculators and the error issues/level of confidence applicable to quantitative reseraches only?Can I apply the same in a qualitative study? For a population of 100,000 or more, you need a sample of 383 to obtain a margin of error of 5% for 95% confidence interval. or I can select some of them? You can calculate it using our online sample size calculator. With your suggestion you have only 115 respondents, so this will not be enough to be representative. This means that you’re safe when you take a sample of 384 or more. in the district, if I want to draw sample in the district for children only, how can I can consider the population size for this age group. What would my sample size need to be for a one-tailed test at a 99% confidence level and 2% margin of error? Furthermore, if you decide to increase your confidence interval and your confidence level, the data of your sample will be less accurate. Again, can I limit my survey to only out of the 10 regions in the country as every region have more than 5 offices. The margin of error associated with your sample sizes is 5,7% for tax payer, 7,1% for employees and 8,7% for practitioners. thanks in advance. I am afraid I will not be able to help you. Therefore, a size of 72 customers will be adequate for deriving meaningful inference in this case. Is you have a large population, your margin of error for a sample size of 210 will not fluctuate that much. Sample Size Calculator to Estimate Population Proportion Sample size to estimate proportion formula is defined as (Z 2 x P (1 - P)) / e 2. Generally, you can note this value from the Z table. If you do not know your proportion p, it is quite common to take 0,5 as a value for p. Some maths: Total population: 5,000 pupils KG to JSS3 = 11 levels = about 450 pupils per level If focusing at KG and P1-P3 = 5 levels = 2,250 pupils (this would make sense, because some pupils with SpLD never reach P4 or higher classes; SAP data shows that many out-of-school children are 13 years and in P3…), ‘At risk’ assessment takes about 45 minutes. Can sir help me these questions? 2. how much from each university? Here are the formulas used in our Sample Size Calculator: Sample Size . Kind regards, Didier. I am doing my thesis on a population of 1406 non government Organizations. E.g. Monitor customer experience (CX), employee experience (EX) and engagement. Hello sir… I have selected two populations for my study, one is the cotton growers and second is textile industry. Commonly for qualitative research 20 to 30 interviews are sufficient. Many thanks in advance. Help please. If you want to compare all schools in the results, you need to use a representative sample size for each school. Whether you include the non-applicables is up to you. Could you help me to calculate my study sample? Dear sir If l have 1600000 population then how I estimate sample size for survey study and I dont understand how calculated z score?.. How I can calculate my sample size and methodology of students selection. In this case my sample size is the same as my population. Divided in 2 clusters. of samples possible if the population is 10 and size of sample to be taken is 3. dev., it is quite common to take 0,5 as a value for the stand. N = Population size, Z = Critical value of the normal distribution at the required confidence level, p = Sample proportion, e = Margin of error Obviously, you cannot predict beforehand what response rate you will achieve.

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