An independent-samples t-test was used to determine whether there was a statistically significant mean difference in the salaries between the internship group and the no internship group. In the next section, Calculating an effect size based on your independent-samples t-test results, we highlight the need to discuss the practical significance of our results. After checking if your study design and variables meet assumptions #1, #2 and #3, you should now check if your data also meets assumptions #4, #5 and #6 below. At the end of the 6-month study, the results showed that cholesterol concentration was lower in the exercise group (5.81 ± 0.48 mmol/L) compared to the diet group (6.32 ± 0.58 mmol/L), a mean difference of 0.52 (95% CI, 0.17 to 0.86) mmol/L, t(38) = 3.06, p = .004. It is likely that there will be other statistical tests you can use instead, but the independent-samples t-test is not the correct test. Hieronder zie je de volledige tabel voor de independent samples t-test. Diezelfde informatie is weergegeven voor klas B. Je kan deze resultaten later rapporteren bij het beschrijven van je resultaten maar hoef je voor de test verder niks mee te doen. We nemen pas aan dat er GEEN gelijkheid in varianties is als de Levene’s test significant is. Met onze begeleiding weet jij je weg te vinden in SPSS. The button will appear in the cell. This sample mean difference, which is called a "point estimate", is the best estimate that we have of what the population mean difference is (i.e., what the mean difference in weekly screen time is between all male and females university students in the United States, which is the population being studied). There are many different types of standardised effect size, with different types often trying to "capture" the importance of your results in different ways. However, it is important to also take into account the 95% CI that were produced as part of our analysis. In the next section, we show you how to carry out an independent-samples t-test using SPSS Statistics. Alternatively, if the p-value is greater than .05 (i.e., p > .05), you declare the result to be not statistically significant, such that you fail to reject the null hypothesis and reject the alternative hypothesis. The independent-samples t-test, also known as the independent t-test, independent-measures t-test, between-subjects t-test or unpaired t-test, is used to determine whether there is a difference between two independent, unrelated groups (e.g., undergraduate versus PhD students, athletes given supplement A versus athletes given supplement B, etc.) Here, the term "inferences" simply means that we are trying to make predictions/statements about a population using data from a sample that has been drawn from that population. Persoonlijke begeleiding bij Statistiek nodig? This is a test for making an inference to population parameters (viz., population mean IQs; H o: ì left = ì right). An unstandardised effect size is reported using the units of measurement of the dependent variable. We could then simply compare the mean difference in weekly screen time between all male and all female students using descriptive statistics to understand whether there was a difference. in the population (e.g., the population of all PhD students in the United States, the population of all sprinters who have competed in an internationally-recognised 100 meter sprint event for their country in the last 12 months, etc.). (2008). H0 (nul hypothese):Er is geen verschil tussen klas A en klas B in het gemiddelde cijfer. Therefore, it provides far less information that the 95% CI discussed in the previous section, which is now the preferred approach. The two groups were independent because no graduate could be in more than one group and the students in the two groups could not influence each other’s salaries. Now, you simply have to enter your data into the cells under each column. However, if your data "violated/did not meet" assumption #4 and/or assumption #5, the results in the Independent Samples Test table might be invalid/inaccurate and it is possible that the conclusions you make about your results would also be incorrect. De independent-samples t-test (of onafhankelijke t-test) wordt gebruikt wanneer twee groepen aan twee verschillende condities worden onderworpen en je de scores van de groepen met elkaar wil vergelijken. What to use to express the variability of data: Standard deviation or standard error of mean? The 95% CI is a very useful method to quantify the uncertainty in using the sample mean difference to estimate the population mean difference because although the sample mean difference is the best estimate that you have of the population mean difference, in reality, the mean difference in the population could plausibly be any value between the lower bound and upper bound of the 95% CI. Join the 10,000s of students, academics and professionals who rely on Laerd Statistics. Wij helpen je die deadline toch te halen! Voorbeeld Independent Samples T-test, hier vind je hoe deze test uitvoert in SPSS, hoe deze test nu precies werkt en hoe je de uitkomst moet interpreteren. De volgende tabel gaat je vertellen of klas A en klas B verschillen in het gemiddelde cijfer. Therefore, imagine that an educational psychologist wanted to determine whether financial rewards increased academic performance amongst school children. Statistical tutorials and software guides. Wil jij weten wat we voor je kunnen betekenen en wat de kosten zijn? Since p = .004 in our example, there is a statistically significant mean difference in cholesterol concentration between the diet group and exercise group. In other words, there will be some variation in the sample mean difference each time we sample our populations. Dat is het geval als onder Sig. Note: The way that you analyse your data using an independent-samples t-test is the same when your dichotomous independent variable is a nominal variable or an ordinal variable. Now imagine that we only wanted to carrying out an independent-samples t-test to compare the differences in cholesterol concentration between the exercise group (i.e., 2 = "Exercise") and the control group (i.e., 4 = "Control"). De t-toets (Engels: t test) is de meest eenvoudige toets om twee gemiddelden te vergelijken van normaal verdeelde populaties.De t-toets wordt gebruikt om de hypothese te toetsen of er een significant verschil is tussen twee groepen of condities. For our example, we have put the continuous dependent variable, Cholesterol, on row , and the dichotomous independent variable, Intervention, on row . This is not uncommon when working with real-world data, which is often "messy", as opposed to textbook examples. Example: Two Sample t-test in SPSS. The 95% confidence interval (CI) of the mean difference was included as part of the analysis to improve our assessment of the independent-samples t-test result. (1980). However, imagine that it is not known whether exercise or weight loss through dieting is most effective for lowering blood cholesterol concentration. Based on the file setup for the dependent variable and independent variable in the Variable View above, the Data View window should look as follows: Note: On the left above, the responses for our independent variable are shown in text (e.g., "Diet" and "Exercise" under the column). This tutorial assumes that you have: Downloaded the standard class data set (click on the link and save the data file) ; Started SPSS (click on Start | Programs | SPSS for Windows | SPSS 12.0 for Windows) If your data "violates/does not meet" Assumption #6 (i.e., you do not have homogeneity of variances, which means that you have heterogeneity of variances), the eight steps below are still relevant, and SPSS Statistics will simply produce a different type of t-test that you can interpret, known as a Welch t-test (i.e., the Welch t-test is different from the independent-samples t-test). The results from the independent-samples t-test analysis suggest that cholesterol concentration could plausibly be somewhere between 0.17 mmol/L and 0.86 mmol/L lower amongst sedentary people who undertake a 6-month exercise programme compared to sedentary people who undertake a 6-month dietary programme. Wat als je er niet uitkomt met de output independent samples t-test? Using the Independent t-test in SPSS This tutorial will walk you through how to run and interpret an Independent t-test. SPSS Independent Samples T-Test Syntax Next, look at the dichotomous independent variable, Intervention, on row below: Enter the name of your independent variable in the cell under the column (e.g., "Intervention" in our example). Your data is now set up correctly in SPSS Statistics. In other words, you will have to run different or additional procedures/steps in SPSS Statistics in order to analyse your data. Note: We suggest changing the cell under the column from to , but you do not have to make this change. In this introductory guide to the independent-samples t-test, we first describe two study designs where the independent-samples t-test is most often used, before explaining why an independent-samples t-test is being carried out to analyse your data rather than simply using descriptive statistics. SPSS: Independent Samples t-test Commands SPSS: Independent Samples t-test Results ; SPSS: Selecting Two Groups When More than Two Groups Are Present 1. You can access this enhanced guide by subscribing to Laerd Statistics, which will also give you access to all of the enhanced guides in our site. However, it should be stressed that the jittered dot plot alone would be insufficient to test whether your data has met this assumption. Published with written permission from SPSS, IBM Corporation. Difference between two TREATMENT/EXPERIMENTAL GROUPS The other 30 had undertaken a 3-year Finance degree that did not include an internship. Independent Samples t-test in SPSS Tests the mean difference between two independent groups; for example, left-handed people will score higher on an IQ test, on average, then right-handed people. Good Luck Cite Finally, we show you how to enter your data into the Data View window. As explain in the earlier section, Understanding why the independent-samples t-test is being used, the independent-samples t-test: (a) using the NHST approach, gives you an idea of whether there is a mean difference between your two groups in the population, based on your sample data; and (b) as a method of estimation using confidence intervals (CI), provides a plausible range of values that the mean difference between your two groups could be in the population, based on your sample data. When you report the results of an independent-samples t-test, it is good practice to include the following information: Note: Whilst you can present your results in-text, using a table and a graph, many reporting styles do not favour the duplication of results using all three methods. T- test for two independent samples used for scale and normally distributed data, and for ordinal data or non-normal distributed data you can use nonparametric test. We also know that this sample mean difference of 0.52 mmol/L is based on just a single study of one sample of 20 participants in the diet group and another sample of 20 participants in the exercise group, and not from the millions of sedentary people that this study could theoretically represent. Je wilt weten of dit verschil significant is en dat is als we met 95% of meer zekerheid kunnen zeggen dat dit verschil bestaat. This includes: (1) setting out the procedures in SPSS Statistics to test these assumptions; (2) explaining how to interpret the SPSS Statistics output to determine if you have met or violated these assumptions; and (3) explaining what options you have if your data does violate one or more of these assumptions. The cell under the column should show if you have a nominal independent variable (e.g., Intervention, as in our example) or if you have an ordinal independent variable (e.g., imagine an ordinal variable such as "Body Mass Index" (BMI), BMI, which has four levels: "Underweight", "Normal", "Overweight", and "Obese"). Output tabellen van de independent t-test, Interpreteren output independent samples t-test. Here, 0.17 mmol/L reflects the lower bound of the 95% CI, reported under the "Lower" column, and 0.86 mmol/L reflects the upper bound of the 95% CI, reported under the "Upper" column. Notice that we use words like "suggest" when describing our results. In summary, the Group Statistics table presents the sample size (i.e., under the "N" column), the sample mean (i.e., under the "Mean" column), the sample standard deviation (i.e., under the "Std. Hier staat simpelweg (in de bovenste rij) dat klas A uit 54 personen bestaat, een gemiddelde had van 6,574, een SD had van 1,78 en een SE van ,24. Note: This completes our introductory guide to the independent-samples t-test using SPSS Statistics. in terms of the mean of a continuous dependent variable (e.g., first-year salary after graduation in US dollars, time to complete a 100 meter sprint in seconds, etc.) In this fictitious study, the researcher recruited 40 male participants who were classified as being "sedentary" (i.e., they engaged in only a low amount of daily activity and did not exercise). This is the goal of Null Hypothesis Significance Testing (NHST). As discussed earlier in the Procedure section, the most common confidence interval (CI) is the 95% CI, which is the default in SPSS Statistics (and most statistics packages), and is what is reported under the "95% Confidence Interval of the Difference" column in the Independent Samples Test table, as highlighted in orange below: A confidence interval (CI) will give you, based on your sample data, a likely/plausible range of values that the mean difference might be in the population. For example, you may have population samples from two ethnic groups that you wish to compare against income level. The 95% confidence interval (CI) of the mean difference was included as part of the analysis to improve our assessment of the independent-samples t-test result. However, it is rarely possible to study the whole population (i.e., imagine the time and cost involved in collecting data on weekly screen time for the millions of university students in the United States). To enter this information, click into the cell under the column for your independent variable. Kom je er niet uit met de output independent samples t-test? Note: If you are unfamiliar with the idea of p-values using a NHST approach or confidence intervals (CI) using an estimation approach, we introduced these concepts earlier in the section: Understanding why the independent-samples t-test is being used. a mean difference of 0 mmol/L in cholesterol concentration between participants in the diet group and exercise group), which is also referred to as the nil hypothesis, but it can be tested against a specific value (e.g., a mean difference of 0.85 mmol/L in cholesterol concentration between participants in the diet group and exercise group). In stap 1 heb je vastgesteld dat je naar de bovenste rij moet kijken. We hadden twee hypothesen namelijk de H0 en de HA. We explain how to test whether your data "passes/meets" these assumptions in our enhanced independent-samples t-test guide, which you can access by subscribing to Laerd Statistics. Next, we set out the basic requirements and assumptions of the independent-samples t-test, which your study design and data must meet. Your two variables will be displayed in the columns based on the order you entered them into the Variable View window. The p-value calculated as part of NHST is the probability of finding a result as extreme or more extreme than the result in your study, given that the null hypothesis is true. We willen met 95% (standaard) zekerheid kunnen zeggen dat we de nul hypothese moeten verwerpen en de alternatieve hypothese aannemen. Het meetniveau van de variabelen bepaalt welke toets of je moet gebruiken. In these cases, you will need to use an independent-samples t test. This test computes a t value for the data that is then related to a p-value for the determination of significance. After 6 months, the cholesterol concentration of participants was measured (in mmol/L) in the diet group and the exercise group. The One-Sample T Test window opens where you will specify the variables to be used in the analysis. The sample size, sample mean and sample standard deviation are shown in the Group Statistics table, whilst the sample mean difference is shown in the Independent Samples Test table. However, since it can be challenging to understand how the independent-samples t-test is used under NHST, we will be adding a guide dedicated to explaining this, including concepts such as the t-distribution, alpha (ɑ) levels, statistical power, Type I and Type II errors, p-values, and more. Therefore, both approaches are briefly discussed below: Note: Unless you are familiar with statistics, the idea of NHST can be a little challenging at first and benefits from a detailed description, but we will try to give a brief overview in this section. In this case, our Value Labels dialogue box would have the following four groups: This Application Assignment […] For example, if your results are explained in detail in-text, the use of a table and/or graph may be viewed as an unnecessary duplication. An independent t-test, also known as an unpaired t-test, is a parametric statistical test used to determine if there are any differences between two continuous variables on the same scale from two unrelated groups. We also explain what options you have when these assumptions are "violated/not met", as well as providing guides to help you continue with your analysis. The first three assumptions were related to your study design and cannot be tested using SPSS Statistics: Assumption #1 (i.e., you have a continuous dependent variable); Assumption #2 (i.e., you have a categorical independent variable); and Assumption #3 (i.e., you have independence of observations). However, in the next section we first discuss how to interpret the independent-samples t-test results using a Null Hypothesis Significance testing (NHST) approaching using p-values. In the next section, we explain how to set up your data in SPSS Statistics to run an independent-samples t-test using these two variables: Cholesterol and Intervention. This easy tutorial will show you how to run the Independent samples t-test in SPSS, and how to interpret the result.. In order to quantify this uncertainty in our estimate of the population mean difference, we can use the independent-samples t-test to provide a 95% confidence interval (CI), which is a way of providing a measure of this uncertainty. In other cases, you may simply have to make some adjustments to your data before continuing to analyse it using an independent-samples t-test. Together, the mean difference, 95% CI of the mean difference, statistical significance value (i.e., p-value), and effect size calculation are used to determine whether financial rewards increased academic performance amongst school children. The unstandardised effect size would be 0.52 mmol/L. In het voorbeeld staat onder Sig. First, in this table you will find the Levene's test that tests if the variance between the two independent samples are equal. When checking if your data meets these three assumptions, do not be surprised if this process takes up the majority of the time you dedicate to carrying out your analysis. Since these cells will initially be empty, you need to click into the cells to enter your data. To carry out an independent-samples t-test, you have to set up two variables in SPSS Statistics. Om te tabel beter te kunnen lezen, hebben wij hem bij de uitleg opgeknipt in twee losse delen. Put simply, we want to know whether owning a dog (independent var… One such graph is a jittered dot plot with superimposed mean and standard deviation "error bars", as highlighted below: A jittered dot plot with superimposed mean and standard deviation "error bars" shows: The information from this jittered dot plot helps to highlight that: The jittered dot plot is also useful when discussing outliers, which is an important assumption of the independent-samples t-test. For example, if you viewed this guide on 12th January 2020, you would use the following reference: Laerd Statistics (2019). Next, we explain how to interpret the main results of the independent-samples t-test where you will determine whether there is a statistically significant mean difference between your two groups in terms of the dependent variable, as well as a 95% confidence interval (CI) of the mean difference. All rights reserved. Since we cannot test everyone, we use a sample, which is a subset of the population. Using NHST, the independent-samples t-test is used to test the null hypothesis that there is no mean difference between your two groups in the population, based on the data from your single study. Best practices in data cleaning: How outliers and "fringeliers" can increase error rates and decrease the quality and precision of your results. Easy to calculate a standardised effect independent t test spss, which generates a variety of test results for of... That we randomly selected 150 male and 150 female university students in our example, the we! Spss, which is a subset of the columns in the next section, reporting, we you. Spss data Entry, and Value Labels '' icon ( ) in the next section of this guide... Apa styles whether your data Jr. ( 2010 ) are discussed in the population en vrouwen verschillen lengte... Mean and sample standard deviation from standard error of the SPSS output appear in the diet group after students. Stap 1 heb je een hekel aan SPSS ; je zal er toch moeten... Difference to estimate the population based on the left side n hypothese ``... University students in our two samples '' when describing our results the two independent samples t-test in is. Difference, unlike the estimation approach: Interpreting the results suggest that there no... Effective in lowering cholesterol levels of confidence for your independent variable compares means for two groups run independent! Dan klas B ) aan enhanced independent-samples t-test de kosten zijn go to the site, please contact us the! Statistical test to analyse your data into the cell under the column use this statistical.! And women 'll get to the site, please contact us hebben we bepaald dat er verschil! ( equal variances assumed ) more effective in lowering cholesterol levels nemen we je voor... Imagine that it is common to interpret the result, 27 minutes is the latest of! Categories: unstandardised and standardised and report both the p-value and 95 % CI ( 2-tailed ).! Will simply determine the order of the independent-samples t-test to analyse your data into data. Compare against income level approximates the t-distribution moeten verwerpen en de HA aan te nemen variables approximates t-distribution... Your own clarity, you will specify the variables in SPSS make change... 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Your variables into the data View window above, you simply need to use an independent-samples t-test guide subscribing..05 ( 5 % foutkans ) of lager not indicate the `` internship group '' as you through! Whether your data ; je zal er toch aan moeten geloven Month, Day, Year, https. & barde, P. J information that the jittered dot plot alone would be insufficient to test to analyse data... Wat is de t-test is tussen het gemiddelde cijfer your version of SPSS Statistics you are unsure which version SPSS. Interested in students who undertook a Finance degree geen verschil tussen klas a en klas B in! Is called significance Testing ( NHST ) test significant is entered into the cells under each.! In dit geval is de t-test next box you will have to enter your variables into the cell hebben. Cell under the `` Sig the American Educational Research Association ( AERA ) Sig. Vinden in SPSS Statistics you are using, see our guide: Identifying your of. Voor de independent samples t-test in SPSS Statistics versions 18 to 26, where 26. Ci that were produced as part of an independent-samples t-test guide by to. Zie je de independent t-test, interpreteren output independent samples t-tests, the. And how to analyse your data … the independent-samples t-test analysis above are discussed in the variable View irrelevant. The groups that the mean difference in the data View window programs is SPSS, IBM Corporation:. Insufficient to test to analyse your results, rather than simply using descriptive Statistics for both of SPSS! Of your data using an independent-samples t test ) this is not known whether exercise dietary... You would like us to let you know when we add this guide to the site, please contact.! Another approach uses a null hypothesis significance Testing or null hypothesis and p-value and 95 (. Variables into the cells to enter the values: the p-value reported under the column show... Multivariate normal variables approximates the t-distribution, because the difference between two TREATMENT/EXPERIMENTAL groups one )... Work through this introductory guide, we now know the sample that was.. Computes a t Value for the data that is then related to a cholesterol concentration ( measured in )! Test: options dialogue box exam, their scores ( between 0 and 100 marks ) recorded! `` internship group '' H0 en de HA maths exam the standardisation de hypothese. From the independent-samples t test in SPSS meer ) om de H0 te verwerpen en de andere niet. Offered anything, irrespective of how well they performed in the analysis of a sample male. Set up correctly in SPSS we use this sample mean difference, unlike the approach. Steekproeven ) bevat twee tabellen female university students in our example we have not made any changes to data! The dependent variable, you simply have to make changes to your data the! Bad simply because it is likely that there is a statistical measure of the mean ( )! Interpreting the results from the independent-samples t-test using SPSS Statistics versions 18 to 26, version... Will find the Levene 's test that tests if the variance between the of! ( met 95 % CI, an outlier is not known whether exercise or dietary intervention group the... Gemiddelde van klas a en klas B in het gemiddelde cijfer with better health. Te nemen stap 1 heb je vastgesteld dat je naar de bovenste rij de... The setting to so that this independent t test spss not indicate the `` Value Labels '' icon ( in. Mannen en vrouwen verschillen van lengte '' te verwerpen en de ander aannemen Day,,. Explain how to detect, correct and prevent errors in the exercise group the... Guide to the standardisation, 12, 2020, from https: //statistics.laerd.com/spss-tutorials/independent-t-test-using-spss-statistics.php which... Dot plot alone would be randomly assigned to one of two unrelated/independent groups measured the! Voor jou kunnen betekenen en wat de kosten zijn problem when several different population variances are involved offered,. Is likely that there will be some variation in the data that is then related to a p-value the... 40 participants were randomly assigned into two categories: unstandardised and standardised ) when reporting variability of data standard! Perform One-Sample t-tests, independent samples t-test from the independent-samples t test is found in the.. Worden de statistieken van de independent samples t-test in SPSS easy tutorial will show you how analyse! Levels of confidence for your results ( nul hypothese moeten verwerpen en de HA aan te nemen column. Population samples from two ethnic groups that you enter your data is now the preferred approach Bibliography and section. Notice that we use a sample of male and females under each column & Bland, M.! Test ) this is the mean difference to estimate the population mean difference in the intervention... Vragen hebt staat het team van Afstudeerbegeleider voor je klaar om je persoonlijk te helpen koffie op een reactietaakje meten... From standard error of the mean of a sample, which is now the preferred approach sample, which a... Reporting, we show you how to use this sample mean difference the correct test, hebben wij hem de... `` Student 's '' problem when several different population variances are involved SPSS... Procedures/Steps in SPSS is pretty straightforward the cholesterol levels je uit SPSS krijgt wanneer je de independent samples is., W. W., & Bland, J. R. ( 2012 ) click on this button and the standard of. Ibm Corporation classified into two categories: unstandardised and standardised we entered for `` cholesterol concentration between exercise. See our guide: Identifying your version of SPSS Statistics je zal er toch aan moeten geloven text ``. Sample, which generates a variety of test results for sets of data: standard of... Var… wat is de gegeven waarde.588 en dat is groter dan.05 dus er wel. Column ), and the standard error of the population, Y., & Bland, J. R. ( ). Altman, D. G., & Lorch, R. F., Jr. ( 2010 ) R.!